qrhi.cpp

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#include "qrhi_p.h"
#include <qmath.h>

#include "qrhinull_p.h"
#ifndef QT_NO_OPENGL
#include "qrhigles2_p.h"
#endif
#if QT_CONFIG(vulkan)
#include "qrhivulkan_p.h"
#endif
#ifdef Q_OS_WIN
#include "qrhid3d11_p.h"
#endif
#ifdef Q_OS_DARWIN
#include "qrhimetal_p.h"
#endif

QT_BEGIN_NAMESPACE

/*!
    \class QRhi
    \inmodule QtRhi

    \brief Accelerated 2D/3D graphics API abstraction.

     QRhi is an abstraction for hardware accelerated graphics APIs, such as,
     \l{https://www.khronos.org/opengl/}{OpenGL},
     \l{https://www.khronos.org/opengles/}{OpenGL ES},
     \l{https://docs.microsoft.com/en-us/windows/desktop/direct3d}{Direct3D},
     \l{https://developer.apple.com/metal/}{Metal}, and
     \l{https://www.khronos.org/vulkan/}{Vulkan}.

    Each QRhi instance is backed by a backend for a specific graphics API. The
    selection of the backend is a run time choice and is up to the application
    or library that creates the QRhi instance. Some backends are available on
    multiple platforms (OpenGL, Vulkan, Null), while APIs specific to a given
    platform are only available when running on the platform in question (Metal
    on macOS/iOS/tvOS, Direct3D on Windows).

    \section2 Design Fundamentals

    A QRhi cannot be instantiated directly. Instead, use the create()
    function. Delete the QRhi instance normally to release the graphics device.

    \section3 Resources

    Instances of classes deriving from QRhiResource, such as, QRhiBuffer,
    QRhiTexture, etc., encapsulate zero, one, or more native graphics
    resources. Instances of such classes are always created via the \c new
    functions of the QRhi, such as, newBuffer(), newTexture(),
    newTextureRenderTarget(), newSwapChain().

    \badcode
        vbuf = rhi->newBuffer(QRhiBuffer::Immutable, QRhiBuffer::VertexBuffer, sizeof(vertexData));
        if (!vbuf->build()) { error }
        ...
        vbuf->releaseAndDestroy();
    \endcode

    \list

    \li The returned value from both create() and functions like newBuffer() is
    owned by the caller.

    \li Unlike QRhi, subclasses of QRhiResource should not be destroyed
    directly via delete without calling QRhiResource::release(). The typical
    approach is to call QRhiResource::releaseAndDestroy(). This is equivalent
    to QRhiResource::release() followed by \c delete.

    \li Just creating a QRhiResource subclass never allocates or initalizes any
    native resources. That is only done when calling the \c build function of a
    subclass, for example, QRhiBuffer::build() or QRhiTexture::build().

    \li The exception is
    QRhiTextureRenderTarget::newCompatibleRenderPassDescriptor() and
    QRhiSwapChain::newCompatibleRenderPassDescriptor(). There is no \c build
    operation for these and the returned object is immediately active.

    \li The resource objects themselves are treated as immutable: once a
    resource is built, changing any parameters via the setters, such as,
    QRhiTexture::setPixelSize(), has no effect, unless the underlying native
    resource is released and \c build is called again. See more about resource
    reuse in the sections below.

    \li The underlying native resources are scheduled for releasing by calling
    QRhiResource::release(). Backends often queue release requests and defer
    executing them to an unspecified time, this is hidden from the
    applications. This way applications do not have to worry about releasing a
    native resource that may still be in use by an in-flight frame.

    \li Note that this does not mean that resources can freely be released
    within a frame (that is, in a
    \l{QRhiCommandBuffer::beginFrame()}{beginFrame()} -
    \l{QRhiCommandBuffer::endFrame()}{endFrame()} section). As a general rule,
    all referenced QRhiResource objects must stay unchanged until the frame is
    submitted by calling \l{QRhiCommandBuffer::endFrame()}{endFrame()}. To ease
    this, QRhiResource::releaseAndDestroyLater() is provided as a convenience.
    This allows applications to safely issue a (defered) releaseAndDestroy()
    while recording a frame.

    \endlist

    \section3 Command buffers and defered command execution

    Regardless of the design and capabilities of the underlying graphics API,
    all QRhi backends implement some level of command buffers. No
    QRhiCommandBuffer function issues any native bind or draw command (such as,
    \c glDrawElements) directly. Commands are always recorded in a queue,
    either native or provided by the QRhi backend. The command buffer is
    submitted, and so execution starts only upon QRhi::endFrame() or
    QRhi::finish().

    The defered nature has consequences for some types of objects. For example,
    writing to a dynamic buffer multiple times within a frame, in case such
    buffers are backed by host-visible memory, will result in making the
    results of all writes are visible to all draw calls in the command buffer
    of the frame, regardless of when the dynamic buffer update was recorded
    relative to a draw call.

    Furthermore, instances of QRhiResource subclasses must be treated immutable
    within a frame in which they are referenced in any way. Create or rebuild
    all resources upfront, before starting to record commands for the next
    frame. Reusing a QRhiResource instance within a frame (by rebuilding it and
    then referencing it again in the same \c{beginFrame - endFrame} section)
    should be avoided as it may lead to unexpected results, depending on the
    backend.

    As a general rule, all referenced QRhiResource objects must stay valid and
    unmodified until the frame is submitted by calling
    \l{QRhiCommandBuffer::endFrame()}{endFrame()}. On the other hand,
    \l{QRhiResource::release()}{release()} or
    \l{QRhiResource::releaseAndDestroy()}{releaseAndDestroy()} are always safe
    to call once the frame is submitted, regardless of the status of the
    underlying native resources (which may still be in use by the GPU - but
    that is taken care of internally).

    Unlike APIs like OpenGL, upload and copy type of commands cannot be mixed
    with draw commands. The typical renderer will involve a sequence similar to
    the following: \c{(re)build resources} - \c{begin frame} - \c{record
    uploads and copies} - \c{start renderpass} - \c{record draw calls} - \c{end
    renderpass} - \c{end frame}. Recording copy type of operations happens via
    QRhiResourceUpdateBatch. Such operations are committed typically on
    \l{QRhiCommandBuffer::beginPass()}{beginPass()}.

    When working with legacy rendering engines designed for OpenGL, the
    migration to QRhi often involves redesigning from having a single \c render
    step (that performs copies and uploads, clears buffers, and issues draw
    calls, all mixed together) to a clearly separated, two phase \c prepare -
    \c render setup where the \c render step only starts a renderpass and
    records draw calls, while all resource creation and queuing of updates,
    uploads and copies happens beforehand, in the \c prepare step.

    \section3 Resource reuse

    From the user's point of view a QRhiResource is reusable immediately after
    calling QRhiResource::release(). With the exception of swapchains, calling
    \c build() on an already built object does an implicit \c release(). This
    provides a handy shortcut to reuse a QRhiResource instance with different
    parameters, with a new native graphics object underneath.

    The importance of reusing the same object lies in the fact that some
    objects reference other objects: for example, a QRhiShaderResourceBindings
    can reference QRhiBuffer, QRhiTexture, and QRhiSampler instances. If in a
    later frame one of these buffers need to be resized or a sampler parameter
    needs changing, destroying and creating a whole new QRhiBuffer or
    QRhiSampler would invalidate all references to the old instance. By just
    changing the appropriate parameters via QRhiBuffer::setSize() or similar
    and then calling QRhiBuffer::build(), everything works as expected and
    there is no need to touch the QRhiShaderResourceBindings at all, even
    though there is a good chance that under the hood the QRhiBuffer is now
    backed by a whole new native buffer.

    \badcode
        ubuf = rhi->newBuffer(QRhiBuffer::Dynamic, QRhiBuffer::UniformBuffer, 256);
        ubuf->build();

        srb = rhi->newShaderResourceBindings()
        srb->setBindings({
            QRhiShaderResourceBinding::uniformBuffer(0, QRhiShaderResourceBinding::VertexStage | QRhiShaderResourceBinding::FragmentStage, ubuf)
        });
        srb->build();

        ...

        // now in a later frame we need to grow the buffer to a larger size
        ubuf->setSize(512);
        ubuf->build(); // same as ubuf->release(); ubuf->build();

        // that's it, srb needs no changes whatsoever
    \endcode

    \section3 Pooled objects

    In addition to resources, there are pooled objects as well, such as,
    QRhiResourceUpdateBatch. An instance is retrieved via a \c next function,
    such as, nextResourceUpdateBatch(). The caller does not own the returned
    instance in this case. The only valid way of operating here is calling
    functions on the QRhiResourceUpdateBatch and then passing it to
    QRhiCommandBuffer::beginPass() or QRhiCommandBuffer::endPass(). These
    functions take care of returning the batch to the pool. Alternatively, a
    batch can be "canceled" and returned to the pool without processing by
    calling QRhiResourceUpdateBatch::release().

    A typical pattern is thus:

    \badcode
        QRhiResourceUpdateBatch *resUpdates = rhi->nextResourceUpdateBatch();
        ...
        resUpdates->updateDynamicBuffer(ubuf, 0, 64, mvp.constData());
        if (!image.isNull()) {
            resUpdates->uploadTexture(texture, image);
            image = QImage();
        }
        ...
        QRhiCommandBuffer *cb = m_sc->currentFrameCommandBuffer();
        cb->beginPass(swapchain->currentFrameRenderTarget(), clearCol, clearDs, resUpdates);
    \endcode

    \section3 Swapchain specifics

    QRhiSwapChain features some special semantics due to the peculiar nature of
    swapchains.

    \list

    \li It has no \c build but rather a QRhiSwapChain::buildOrResize().
    Repeatedly calling this function is \b not the same as calling
    QRhiSwapChain::release() followed by QRhiSwapChain::buildOrResize(). This
    is because swapchains often have ways to handle the case where buffers need
    to be resized in a manner that is more efficient than a brute force
    destroying and recreating from scratch.

    \li An active QRhiSwapChain must be released by calling
    QRhiSwapChain::release() whenever the targeted QWindow sends the
    QPlatformSurfaceEvent::SurfaceAboutToBeDestroyed event. It should not be
    postponed since releasing the swapchain may become problematic when the
    native window is not around anymore (e.g. because the QPlatformWindow got
    destroyed already when getting a QWindow::close())

    \endlist

    \section3 Ownership

    The general rule is no ownership transfer. Creating a QRhi with an already
    existing graphics device does not mean the QRhi takes ownership of the
    device object. Similarly, ownership is not given away when a device or
    texture object is "exported" via QRhi::nativeHandles() or
    QRhiTexture::nativeHandles(). Most importantly, passing pointers in structs
    and via setters does not transfer ownership.

    \section3 Threading

    A QRhi instance and the associated resources can be created and used on any
    thread but all usage must be limited to that one single thread. When
    rendering to multiple QWindows in an application, having a dedicated thread
    and QRhi instance for each window is often advisable, as this can eliminate
    issues with unexpected throttling caused by presenting to multiple windows.

    When it comes to externally created native objects, such as OpenGL contexts
    passed in via QRhiGles2NativeHandles, it is up to the application to ensure
    they are not misused by other threads.

    Resources are not shareable between QRhi instances. This is an intentional
    choice since QRhi hides most queue, command buffer, and resource
    synchronization related tasks, and provides no API for them. Safe and
    efficient concurrent use of graphics resources from multiple threads is
    tied deeply to those concepts, however, and is thus a topic that is
    currently out of scope, but may be introduced in the future.
 */

/*!
    \enum QRhi::Implementation
    Describes which graphics API-specific backend gets used by a QRhi instance.

    \value Null
    \value Vulkan
    \value OpenGLES2
    \value D3D11
    \value Metal
 */

/*!
    \enum QRhi::Flag
    Describes what special features to enable.

    \value EnableProfiling Enables gathering timing (CPU, GPU) and resource
    (QRhiBuffer, QRhiTexture, etc.) information and additional metadata. See
    QRhiProfiler. Avoid enabling in production builds as it may involve a
    performance penalty.

    \value EnableDebugMarkers Enables debug marker groups. Without this frame
    debugging features like making debug groups and custom resource name
    visible in external GPU debugging tools will not be available and functions
    like QRhiCommandBuffer::debugMarkBegin() will become a no-op. Avoid
    enabling in production builds as it may involve a performance penalty.
 */

/*!
    \enum QRhi::FrameOpResult
    Describes the result of operations that can have a soft failure.

    \value FrameOpSuccess Success

    \value FrameOpError Unspecified error

    \value FrameOpSwapChainOutOfDate The swapchain is in an inconsistent state
    internally. This can be recoverable by attempting to repeat the operation
    (such as, beginFrame()) later.

    \value FrameOpDeviceLost The graphics device was lost. This can be
    recoverable by attempting to repeat the operation (such as, beginFrame())
    and releasing and reinitializing all objects backed by native graphics
    resources.
 */

/*!
    \enum QRhi::Feature
    Flag values to indicate what features are supported by the backend currently in use.

    \value MultisampleTexture Indicates that textures with a sample count larger
    than 1 are supported.

    \value MultisampleRenderBuffer Indicates that renderbuffers with a sample
    count larger than 1 are supported.

    \value DebugMarkers Indicates that debug marker groups (and so
    QRhiCommandBuffer::debugMarkBegin()) are supported.

    \value Timestamps Indicates that command buffer timestamps are supported.
    Relevant for QRhiProfiler::gpuFrameTimes().

    \value Instancing Indicates that instanced drawing is supported.

    \value CustomInstanceStepRate Indicates that instance step rates other than
    1 are supported.

    \value PrimitiveRestart Indicates that restarting the assembly of
    primitives when encountering an index value of 0xFFFF
    (\l{QRhiCommandBuffer::IndexUInt16}{IndexUInt16}) or 0xFFFFFFFF
    (\l{QRhiCommandBuffer::IndexUInt32}{IndexUInt32}) is enabled, for certain
    primitive topologies at least. QRhi will try to enable this with all
    backends, but in some cases it will not be supported. Dynamically
    controlling primitive restart is not possible since with some APIs
    primitive restart with a fixed index is always on. Applications must assume
    that whenever this feature is reported as supported, the above mentioned
    index values \c may be treated specially, depending on the topology. The
    only two topologies where primitive restart is guaranteed to behave
    identically across backends, as long as this feature is reported as
    supported, are \l{QRhiGraphicsPipeline::LineStrip}{LineStrip} and
    \l{QRhiGraphicsPipeline::TriangleStrip}{TriangleStrip}.

    \value GeometryShaders Indicates that geometry shaders are supported.

    \value TessellationShaders Indicates that tessellation control and
    evaluation shaders are supported.

    \value NonDynamicUniformBuffers Indicates that creating buffers with the
    usage \l{QRhiBuffer::UniformBuffer}{UniformBuffer} and the types
    \l{QRhiBuffer::Immutable}{Immutable} or \l{QRhiBuffer::Static}{Static} is
    supported. When reported as unsupported, uniform (constant) buffers must be
    created as \l{QRhiBuffer::Dynamic}{Dynamic}. (which is recommended
    regardless)

    \value NonFourAlignedEffectiveIndexBufferOffset Indicates that effective
    index buffer offsets (\c{indexOffset + firstIndex * indexComponentSize})
    that are not 4 byte aligned are supported. When not supported, attempting
    to issue a \l{QRhiCommandBuffer::drawIndexed()}{drawIndexed()} with a
    non-aligned effective offset may lead to unspecified behavior.

    \value NPOTTextureRepeat Indicates that the \l{QRhiSampler::Repeat}{Repeat}
    mode is supported for textures with a non-power-of-two size.

    \value RedOrAlpha8IsRed Indicates that the
    \l{QRhiTexture::RED_OR_ALPHA8}{RED_OR_ALPHA8} format maps to a one
    component 8-bit \c red format. This is the case for all backends except
    OpenGL, where \c{GL_ALPHA}, a one component 8-bit \c alpha format, is used
    instead. This is relevant for shader code that samples from the texture.
 */

/*!
    \enum QRhi::BeginFrameFlag
    Flag values for QRhi::beginFrame()
 */

/*!
    \enum QRhi::EndFrameFlag
    Flag values for QRhi::endFrame()

    \value SkipPresent Specifies that no present command is to be queued or no
    swapBuffers call is to be made. This way no image is presented. Generating
    multiple frames with all having this flag set is not recommended (except,
    for example, for benchmarking purposes - but keep in mind that backends may
    behave differently when it comes to waiting for command completion without
    presenting so the results are not comparable between them)
 */

/*!
    \enum QRhi::ResourceLimit
    Describes the resource limit to query.

    \value TextureSizeMin Minimum texture width and height. This is typically
    1. The minimum texture size is handled gracefully, meaning attempting to
    create a texture with an empty size will instead create a texture with the
    minimum size.

    \value TextureSizeMax Maximum texture width and height. This depends on the
    graphics API and sometimes the platform or implementation as well.
    Typically the value is in the range 4096 - 16384. Attempting to create
    textures larger than this is expected to fail.

    \value MaxColorAttachments The maximum number of color attachments for a
    QRhiTextureRenderTarget, in case multiple render targets are supported. When
    MRT is not supported, the value is 1. Otherwise this is typically 8, but
    watch out for the fact that OpenGL only mandates 4 as the minimum, and that
    is what some OpenGL ES implementations provide.
 */

/*!
    \class QRhiInitParams
    \inmodule QtRhi
    \brief Base class for backend-specific initialization parameters.

    Contains fields that are relevant to all backends.
 */

/*!
    \class QRhiColorClearValue
    \inmodule QtRhi
    \brief Specifies a clear color for a color buffer.
 */

/*!
    Constructs a color clear value with \c{(0, 0, 0, 1)} (opaque black).
 */
QRhiColorClearValue::QRhiColorClearValue()
    : m_rgba(0, 0, 0, 1)
{
}

/*!
    Constructs a color clear value with the floating point color components
    (\c{0.0f - 1.0f}) specified in \a c.
  */
QRhiColorClearValue::QRhiColorClearValue(const QVector4D &c)
    : m_rgba(c)
{
}

/*!
    Constructs a color clear value with the floating point color components
    (\c{0.0f - 1.0f}) specified in \a r, \a g, \a b, and \a a.
 */
QRhiColorClearValue::QRhiColorClearValue(float r, float g, float b, float a)
    : m_rgba(r, g, b, a)
{
}

/*!
    \return \c true if the colors in the two QRhiColorClearValue objects \a a
    and \a b are equal.

    \relates QRhiColorClearValue
 */
bool operator==(const QRhiColorClearValue &a, const QRhiColorClearValue &b) Q_DECL_NOTHROW
{
    return a.rgba() == b.rgba();
}

/*!
    \return \c false if the colors in the two QRhiColorClearValue objects \a a
    and \a b are equal; otherwise returns \c true.

    \relates QRhiColorClearValue
*/
bool operator!=(const QRhiColorClearValue &a, const QRhiColorClearValue &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiColorClearValue
 */
uint qHash(const QRhiColorClearValue &v, uint seed) Q_DECL_NOTHROW
{
    const QVector4D c = v.rgba();
    return qFloor((c.x() + c.y() + c.z() + c.w()) * 1000) + seed;
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiColorClearValue &v)
{
    QDebugStateSaver saver(dbg);
    const QVector4D c = v.rgba();
    dbg.nospace() << "QRhiColorClearValue(r=" << c.x()
                  << " g=" << c.y()
                  << " b=" << c.z()
                  << " a=" << c.w()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiDepthStencilClearValue
    \inmodule QtRhi
    \brief Specifies clear values for a depth or stencil buffer.
 */

/*!
    Constructs a depth/stencil clear value with depth clear value 1.0f and
    stencil clear value 0.
 */
QRhiDepthStencilClearValue::QRhiDepthStencilClearValue()
    : m_d(1),
      m_s(0)
{
}

/*!
    Constructs a depth/stencil clear value with depth clear value \a d and
    stencil clear value \a s.
 */
QRhiDepthStencilClearValue::QRhiDepthStencilClearValue(float d, quint32 s)
    : m_d(d),
      m_s(s)
{
}

/*!
    \return \c true if the values in the two QRhiDepthStencilClearValue objects
    \a a and \a b are equal.

    \relates QRhiDepthStencilClearValue
 */
bool operator==(const QRhiDepthStencilClearValue &a, const QRhiDepthStencilClearValue &b) Q_DECL_NOTHROW
{
    return a.depthClearValue() == b.depthClearValue()
            && a.stencilClearValue() == b.stencilClearValue();
}

/*!
    \return \c false if the values in the two QRhiDepthStencilClearValue
    objects \a a and \a b are equal; otherwise returns \c true.

    \relates QRhiDepthStencilClearValue
*/
bool operator!=(const QRhiDepthStencilClearValue &a, const QRhiDepthStencilClearValue &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiDepthStencilClearValue
 */
uint qHash(const QRhiDepthStencilClearValue &v, uint seed) Q_DECL_NOTHROW
{
    return seed * (qFloor(v.depthClearValue() * 100) + v.stencilClearValue());
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiDepthStencilClearValue &v)
{
    QDebugStateSaver saver(dbg);
    dbg.nospace() << "QRhiDepthStencilClearValue(depth-clear=" << v.depthClearValue()
                  << " stencil-clear=" << v.stencilClearValue()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiViewport
    \inmodule QtRhi
    \brief Specifies a viewport rectangle.

    Used with QRhiCommandBuffer::setViewport().

    \note QRhi assumes OpenGL-style viewport coordinates, meaning x and y are
    bottom-left.

    Typical usage is like the following:

    \badcode
      const QSize outputSizeInPixels = swapchain->currentPixelSize();
      const QRhiViewport viewport(0, 0, outputSizeInPixels.width(), outputSizeInPixels.height());
      cb->beginPass(swapchain->currentFrameRenderTarget(), { 0, 0, 0, 1 }, { 1, 0 });
      cb->setGraphicsPipeline(ps);
      cb->setViewport(viewport);
      ...
    \endcode

    \sa QRhiCommandBuffer::setViewport(), QRhi::clipSpaceCorrMatrix(), QRhiScissor
 */

/*!
    Constructs a viewport description with a default rectangle and depth range.
    The default depth range is 0.0f - 1.0f.

    \sa QRhi::clipSpaceCorrMatrix()
 */
QRhiViewport::QRhiViewport()
    : m_rect(0, 0, 1280, 720),
      m_minDepth(0),
      m_maxDepth(1)
{
}

/*!
    Constructs a viewport description with the rectangle specified by \a x, \a
    y, \a w, \a h and the depth range \a minDepth and \a maxDepth.

    \note x and y are assumed to be the bottom-left position.

    \sa QRhi::clipSpaceCorrMatrix()
 */
QRhiViewport::QRhiViewport(float x, float y, float w, float h, float minDepth, float maxDepth)
    : m_rect(x, y, w, h),
      m_minDepth(minDepth),
      m_maxDepth(maxDepth)
{
}

/*!
    \return \c true if the values in the two QRhiViewport objects
    \a a and \a b are equal.

    \relates QRhiViewport
 */
bool operator==(const QRhiViewport &a, const QRhiViewport &b) Q_DECL_NOTHROW
{
    return a.viewport() == b.viewport()
            && a.minDepth() == b.minDepth()
            && a.maxDepth() == b.maxDepth();
}

/*!
    \return \c false if the values in the two QRhiViewport
    objects \a a and \a b are equal; otherwise returns \c true.

    \relates QRhiViewport
*/
bool operator!=(const QRhiViewport &a, const QRhiViewport &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiViewport
 */
uint qHash(const QRhiViewport &v, uint seed) Q_DECL_NOTHROW
{
    const QVector4D r = v.viewport();
    return seed + r.x() + r.y() + r.z() + r.w() + qFloor(v.minDepth() * 100) + qFloor(v.maxDepth() * 100);
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiViewport &v)
{
    QDebugStateSaver saver(dbg);
    const QVector4D r = v.viewport();
    dbg.nospace() << "QRhiViewport(bottom-left-x=" << r.x()
                  << " bottom-left-y=" << r.y()
                  << " width=" << r.z()
                  << " height=" << r.w()
                  << " minDepth=" << v.minDepth()
                  << " maxDepth=" << v.maxDepth()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiScissor
    \inmodule QtRhi
    \brief Specifies a scissor rectangle.

    Used with QRhiCommandBuffer::setScissor(). Setting a scissor rectangle is
    only possible with a QRhiGraphicsPipeline that has
    QRhiGraphicsPipeline::UsesScissor set.

    \note QRhi assumes OpenGL-style scissor coordinates, meaning x and y are
    bottom-left.

    \sa QRhiCommandBuffer::setScissor(), QRhiViewport
 */

/*!
    Constructs an empty scissor.
 */
QRhiScissor::QRhiScissor()
{
}

/*!
    Constructs a scissor with the rectangle specified by \a x, \a y, \a w, and
    \a h.

    \note x and y are assumed to be the bottom-left position.
 */
QRhiScissor::QRhiScissor(int x, int y, int w, int h)
    : m_rect(x, y, w, h)
{
}

/*!
    \return \c true if the values in the two QRhiScissor objects
    \a a and \a b are equal.

    \relates QRhiScissor
 */
bool operator==(const QRhiScissor &a, const QRhiScissor &b) Q_DECL_NOTHROW
{
    return a.scissor() == b.scissor();
}

/*!
    \return \c false if the values in the two QRhiScissor
    objects \a a and \a b are equal; otherwise returns \c true.

    \relates QRhiScissor
*/
bool operator!=(const QRhiScissor &a, const QRhiScissor &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiScissor
 */
uint qHash(const QRhiScissor &v, uint seed) Q_DECL_NOTHROW
{
    const QVector4D r = v.scissor();
    return seed + r.x() + r.y() + r.z() + r.w();
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiScissor &s)
{
    QDebugStateSaver saver(dbg);
    const QVector4D r = s.scissor();
    dbg.nospace() << "QRhiScissor(bottom-left-x=" << r.x()
                  << " bottom-left-y=" << r.y()
                  << " width=" << r.z()
                  << " height=" << r.w()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiVertexInputBinding
    \inmodule QtRhi
    \brief Describes a vertex input binding.

    Specifies the stride (in bytes, must be a multiple of 4), the
    classification and optionally the instance step rate.

    As an example, assume a vertex shader with the following inputs:

    \badcode
        layout(location = 0) in vec4 position;
        layout(location = 1) in vec2 texcoord;
    \endcode

    Now let's assume also that 3 component vertex positions \c{(x, y, z)} and 2
    component texture coordinates \c{(u, v)} are provided in a non-interleaved
    format in a buffer (or separate buffers even). Definining two bindings
    could then be done like this:

    \badcode
        QRhiVertexInputLayout inputLayout;
        inputLayout.setBindings({
            { 3 * sizeof(float) },
            { 2 * sizeof(float) }
        });
    \endcode

    Only the stride is interesting here since instancing is not used. The
    binding number is given by the index of the QRhiVertexInputBinding
    element in the bindings vector of the QRhiVertexInputLayout.

    Once a graphics pipeline with this vertex input layout is bound, the vertex
    inputs could be set up like the following for drawing a cube with 36
    vertices, assuming we have a single buffer with first the positions and
    then the texture coordinates:

    \badcode
        cb->setVertexInput(0, { { cubeBuf, 0 }, { cubeBuf, 36 * 3 * sizeof(float) } });
    \endcode

    Note how the index defined by \c {startBinding + i}, where \c i is the
    index in the second argument of
    \l{QRhiCommandBuffer::setVertexInput()}{setVertexInput()}, matches the
    index of the corresponding entry in the \c bindings vector of the
    QRhiVertexInputLayout.

    \note the stride must always be a multiple of 4.

    \sa QRhiCommandBuffer::setVertexInput()
 */

/*!
    \enum QRhiVertexInputBinding::Classification
    Describes the input data classification.

    \value PerVertex Data is per-vertex
    \value PerInstance Data is per-instance
 */

/*!
    Constructs an empty vertex input binding description.
 */
QRhiVertexInputBinding::QRhiVertexInputBinding()
{
}

/*!
    Constructs a vertex input binding description with the specified \a stride,
    classification \a cls, and instance step rate \a stepRate.

    \note \a stepRate other than 1 is only supported when
    QRhi::CustomInstanceStepRate is reported to be supported.
 */
QRhiVertexInputBinding::QRhiVertexInputBinding(quint32 stride, Classification cls, int stepRate)
    : m_stride(stride),
      m_classification(cls),
      m_instanceStepRate(stepRate)
{
}

/*!
    \return \c true if the values in the two QRhiVertexInputBinding objects
    \a a and \a b are equal.

    \relates QRhiVertexInputBinding
 */
bool operator==(const QRhiVertexInputBinding &a, const QRhiVertexInputBinding &b) Q_DECL_NOTHROW
{
    return a.stride() == b.stride()
            && a.classification() == b.classification()
            && a.instanceStepRate() == b.instanceStepRate();
}

/*!
    \return \c false if the values in the two QRhiVertexInputBinding
    objects \a a and \a b are equal; otherwise returns \c true.

    \relates QRhiVertexInputBinding
*/
bool operator!=(const QRhiVertexInputBinding &a, const QRhiVertexInputBinding &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiVertexInputBinding
 */
uint qHash(const QRhiVertexInputBinding &v, uint seed) Q_DECL_NOTHROW
{
    return seed + v.stride() + v.classification();
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiVertexInputBinding &b)
{
    QDebugStateSaver saver(dbg);
    dbg.nospace() << "QRhiVertexInputBinding(stride=" << b.stride()
                  << " cls=" << b.classification()
                  << " step-rate=" << b.instanceStepRate()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiVertexInputAttribute
    \inmodule QtRhi
    \brief Describes a single vertex input element.

    The members specify the binding number, location, format, and offset for a
    single vertex input element.

    \note For HLSL it is assumed that the vertex shader uses
    \c{TEXCOORD<location>} as the semantic for each input. Hence no separate
    semantic name and index.

    As an example, assume a vertex shader with the following inputs:

    \badcode
        layout(location = 0) in vec4 position;
        layout(location = 1) in vec2 texcoord;
    \endcode

    Now let's assume that we have 3 component vertex positions \c{(x, y, z)}
    and 2 component texture coordinates \c{(u, v)} are provided in a
    non-interleaved format in a buffer (or separate buffers even). Once two
    bindings are defined, the attributes could be specified as:

    \badcode
        QRhiVertexInputLayout inputLayout;
        inputLayout.setBindings({
            { 3 * sizeof(float) },
            { 2 * sizeof(float) }
        });
        inputLayout.setAttributes({
            { 0, 0, QRhiVertexInputAttribute::Float3, 0 },
            { 1, 1, QRhiVertexInputAttribute::Float2, 0 }
        });
    \endcode

    Once a graphics pipeline with this vertex input layout is bound, the vertex
    inputs could be set up like the following for drawing a cube with 36
    vertices, assuming we have a single buffer with first the positions and
    then the texture coordinates:

    \badcode
        cb->setVertexInput(0, { { cubeBuf, 0 }, { cubeBuf, 36 * 3 * sizeof(float) } });
    \endcode

    When working with interleaved data, there will typically be just one
    binding, with multiple attributes refering to that same buffer binding
    point:

    \badcode
        QRhiVertexInputLayout inputLayout;
        inputLayout.setBindings({
            { 5 * sizeof(float) }
        });
        inputLayout.setAttributes({
            { 0, 0, QRhiVertexInputAttribute::Float3, 0 },
            { 0, 1, QRhiVertexInputAttribute::Float2, 3 * sizeof(float) }
        });
    \endcode

    and then:

    \badcode
        cb->setVertexInput(0, { { interleavedCubeBuf, 0 } });
    \endcode

    \sa QRhiCommandBuffer::setVertexInput()
 */

/*!
    \enum QRhiVertexInputAttribute::Format
    Specifies the type of the element data.

    \value Float4 Four component float vector
    \value Float3 Three component float vector
    \value Float2 Two component float vector
    \value Float Float
    \value UNormByte4 Four component normalized unsigned byte vector
    \value UNormByte2 Two component normalized unsigned byte vector
    \value UNormByte Normalized unsigned byte
 */

/*!
    Constructs an empty vertex input attribute description.
 */
QRhiVertexInputAttribute::QRhiVertexInputAttribute()
{
}

/*!
    Constructs a vertex input attribute description with the specified \a
    binding number, \a location, \a format, and \a offset.
 */
QRhiVertexInputAttribute::QRhiVertexInputAttribute(int binding, int location, Format format, quint32 offset)
    : m_binding(binding),
      m_location(location),
      m_format(format),
      m_offset(offset)
{
}

/*!
    \return \c true if the values in the two QRhiVertexInputAttribute objects
    \a a and \a b are equal.

    \relates QRhiVertexInputAttribute
 */
bool operator==(const QRhiVertexInputAttribute &a, const QRhiVertexInputAttribute &b) Q_DECL_NOTHROW
{
    return a.binding() == b.binding()
            && a.location() == b.location()
            && a.format() == b.format()
            && a.offset() == b.offset();
}

/*!
    \return \c false if the values in the two QRhiVertexInputAttribute
    objects \a a and \a b are equal; otherwise returns \c true.

    \relates QRhiVertexInputAttribute
*/
bool operator!=(const QRhiVertexInputAttribute &a, const QRhiVertexInputAttribute &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiVertexInputAttribute
 */
uint qHash(const QRhiVertexInputAttribute &v, uint seed) Q_DECL_NOTHROW
{
    return seed + v.binding() + v.location() + v.format() + v.offset();
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiVertexInputAttribute &a)
{
    QDebugStateSaver saver(dbg);
    dbg.nospace() << "QRhiVertexInputAttribute(binding=" << a.binding()
                  << " location=" << a.location()
                  << " format=" << a.format()
                  << " offset=" << a.offset()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiVertexInputLayout
    \inmodule QtRhi
    \brief Describes the layout of vertex inputs consumed by a vertex shader.

    The vertex input layout is defined by the collections of
    QRhiVertexInputBinding and QRhiVertexInputAttribute.
 */

/*!
    Constructs an empty vertex input layout description.
 */
QRhiVertexInputLayout::QRhiVertexInputLayout()
{
}

/*!
    \return \c true if the values in the two QRhiVertexInputLayout objects
    \a a and \a b are equal.

    \relates QRhiVertexInputLayout
 */
bool operator==(const QRhiVertexInputLayout &a, const QRhiVertexInputLayout &b) Q_DECL_NOTHROW
{
    return a.bindings() == b.bindings()
            && a.attributes() == b.attributes();
}

/*!
    \return \c false if the values in the two QRhiVertexInputLayout
    objects \a a and \a b are equal; otherwise returns \c true.

    \relates QRhiVertexInputLayout
*/
bool operator!=(const QRhiVertexInputLayout &a, const QRhiVertexInputLayout &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiVertexInputLayout
 */
uint qHash(const QRhiVertexInputLayout &v, uint seed) Q_DECL_NOTHROW
{
    return qHash(v.bindings(), seed) + qHash(v.attributes(), seed);
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiVertexInputLayout &v)
{
    QDebugStateSaver saver(dbg);
    dbg.nospace() << "QRhiVertexInputLayout(bindings=" << v.bindings()
                  << " attributes=" << v.attributes()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiGraphicsShaderStage
    \inmodule QtRhi
    \brief Specifies the type and the shader code for a shader stage in the graphics pipeline.

    \note Some backends only support a subset of the stages. Use
    QRhi::isFeatureSupported() to query for support at runtime. For example,
    Metal has no geometry shader support, while the OpenGL 2.x backend only
    supports the vertex and fragment stages.
 */

/*!
    \enum QRhiGraphicsShaderStage::Type
    Specifies the type of the shader stage.

    \value Vertex Vertex stage
    \value Fragment Fragment (pixel) stage
    \value Geometry Geometry stage
    \value TessellationControl Tessellation control (hull) stage
    \value TessellationEvaluation Tessellation evaluation (domain) stage
 */

/*!
    Constructs an empty shader stage description.
 */
QRhiGraphicsShaderStage::QRhiGraphicsShaderStage()
{
}

/*!
    Constructs a shader stage description with the \a type of the stage and the
    \a shader.

    The shader variant \a v defaults to QBakedShaderKey::StandardShader. A
    QBakedShader pack contains multiple source and binary versions of a shader.
    In addition, it can also contain variants of the shader with slightly
    modified code. \a v can then be used to select the desired variant.
 */
QRhiGraphicsShaderStage::QRhiGraphicsShaderStage(Type type, const QBakedShader &shader, QBakedShaderKey::ShaderVariant v)
    : m_type(type),
      m_shader(shader),
      m_shaderVariant(v)
{
}

/*!
    \return \c true if the values in the two QRhiGraphicsShaderStage objects
    \a a and \a b are equal.

    \relates QRhiGraphicsShaderStage
 */
bool operator==(const QRhiGraphicsShaderStage &a, const QRhiGraphicsShaderStage &b) Q_DECL_NOTHROW
{
    return a.type() == b.type()
            && a.shader() == b.shader()
            && a.shaderVariant() == b.shaderVariant();
}

/*!
    \return \c false if the values in the two QRhiGraphicsShaderStage
    objects \a a and \a b are equal; otherwise returns \c true.

    \relates QRhiGraphicsShaderStage
*/
bool operator!=(const QRhiGraphicsShaderStage &a, const QRhiGraphicsShaderStage &b) Q_DECL_NOTHROW
{
    return !(a == b);
}

/*!
    \return the hash value for \a v, using \a seed to seed the calculation.

    \relates QRhiGraphicsShaderStage
 */
uint qHash(const QRhiGraphicsShaderStage &v, uint seed) Q_DECL_NOTHROW
{
    return v.type() + qHash(v.shader(), seed) + v.shaderVariant();
}

#ifndef QT_NO_DEBUG_STREAM
QDebug operator<<(QDebug dbg, const QRhiGraphicsShaderStage &s)
{
    QDebugStateSaver saver(dbg);
    dbg.nospace() << "QRhiGraphicsShaderStage(type=" << s.type()
                  << " shader=" << s.shader()
                  << " variant=" << s.shaderVariant()
                  << ')';
    return dbg;
}
#endif

/*!
    \class QRhiColorAttachment
    \inmodule QtRhi
    \brief Describes the a single color attachment of a render target.

    A color attachment is either a QRhiTexture or a QRhiRenderBuffer. The
    former, when texture() is set, is used in most cases.

    \note texture() and renderBuffer() cannot be both set (be non-null at the
    same time).

    Setting renderBuffer instead is recommended only when multisampling is
    needed. Relying on QRhi::MultisampleRenderBuffer is a better choice than
    QRhi::MultisampleTexture in practice since the former is available in more
    run time configurations (e.g. when running on OpenGL ES 3.0 which has no
    support for multisample textures, but does support multisample
    renderbuffers).

    When targeting a non-multisample texture, the layer() and level()
    indicate the targeted layer (face index \c{0-5} for cubemaps) and mip
    level.

    When texture() or renderBuffer() is multisample, resolveTexture() can be
    set optionally. When set, samples are resolved automatically into that
    (non-multisample) texture at the end of the render pass. When rendering
    into a multisample renderbuffers, this is the only way to get resolved,
    non-multisample content out of them. Multisample textures allow sampling in
    shaders so for them this is just one option.

    \note when resolving is enabled, the multisample data may not be written
    out at all. This means that the multisample texture() must not be used
    afterwards with shaders for sampling when resolveTexture() is set.
 */

/*!
    Constructs an empty color attachment description.
 */
QRhiColorAttachment::QRhiColorAttachment()
{
}

/*!
    Constructs a color attachment description that specifies \a texture as the
    associated color buffer.
 */
QRhiColorAttachment::QRhiColorAttachment(QRhiTexture *texture)
    : m_texture(texture)
{
}

/*!
    Constructs a color attachment description that specifies \a renderBuffer as
    the associated color buffer.
 */
QRhiColorAttachment::QRhiColorAttachment(QRhiRenderBuffer *renderBuffer)
    : m_renderBuffer(renderBuffer)
{
}

/*!
    \class QRhiTextureRenderTargetDescription
    \inmodule QtRhi
    \brief Describes the color and depth or depth/stencil attachments of a render target.

    A texture render target has zero or more textures as color attachments,
    zero or one renderbuffer as combined depth/stencil buffer or zero or one
    texture as depth buffer.

    \note depthStencilBuffer() and depthTexture() cannot be both set (cannot be
    non-null at the same time).
 */

/*!
    Constructs an empty texture render target description.
 */
QRhiTextureRenderTargetDescription::QRhiTextureRenderTargetDescription()
{
}

/*!
    Constructs a texture render target description with one attachment
    described by \a colorAttachment.
 */
QRhiTextureRenderTargetDescription::QRhiTextureRenderTargetDescription(const QRhiColorAttachment &colorAttachment)
{
    m_colorAttachments.append(colorAttachment);
}

/*!
    Constructs a texture render target description with two attachments, a
    color attachment described by \a colorAttachment, and a depth/stencil
    attachment with \a depthStencilBuffer.
 */
QRhiTextureRenderTargetDescription::QRhiTextureRenderTargetDescription(const QRhiColorAttachment &colorAttachment,
                                                                       QRhiRenderBuffer *depthStencilBuffer)
    : m_depthStencilBuffer(depthStencilBuffer)
{
    m_colorAttachments.append(colorAttachment);
}

/*!
    Constructs a texture render target description with two attachments, a
    color attachment described by \a colorAttachment, and a depth attachment
    with \a depthTexture.

    \note \a depthTexture must have a suitable format, such as QRhiTexture::D16
    or QRhiTexture::D32F.
 */
QRhiTextureRenderTargetDescription::QRhiTextureRenderTargetDescription(const QRhiColorAttachment &colorAttachment,
                                                                       QRhiTexture *depthTexture)
    : m_depthTexture(depthTexture)
{
    m_colorAttachments.append(colorAttachment);
}

/*!
    \class QRhiTextureMipLevel
    \inmodule QtRhi
    \brief Describes one mip level in a layer in a texture upload operation.

    The source content is specified either as a QImage or as a raw blob. The
    former is only allowed for uncompressed textures with a format that can be
    mapped to QImage, while the latter is only supported for floating point and
    compressed textures.

    \note image() and data() cannot be both set at the same time.

    destinationTopLeft() specifies the top-left corner of the target
    rectangle. Defaults to (0, 0).

    An empty sourceSize() (the default) indicates that size is assumed to be
    the size of the subresource. For uncompressed textures this implies that
    the size of the source image() must match the subresource. For floating
    point and compressed textures sufficient amount of data must be provided in
    data().

    \note With compressed textures the first upload must always match the
    subresource size due to graphics API limitations with some backends.

    sourceTopLeft() is supported only for uncompressed, non-floating point
    textures, and specifies the top-left corner of the source rectangle.

    \note Setting sourceSize() or sourceTopLeft() may trigger a QImage copy
    internally, depending on the format and the backend.
 */

/*!
    Constructs an empty mip level description.
 */
QRhiTextureMipLevel::QRhiTextureMipLevel()
{
}

/*!
    Constructs a mip level description with a \a image.

    The \l{QImage::size()}{size} of \a image must match the size of the mip
    level. For level 0 that is the \l{QRhiTexture::pixelSize()}{texture size}.

    The bit depth of \a image must be compatible with the
    \l{QRhiTexture::Format}{texture format}.

    To describe a partial upload, call setSourceSize(), setSourceTopLeft(), or
    setDestinationTopLeft() afterwards.
 */
QRhiTextureMipLevel::QRhiTextureMipLevel(const QImage &image)
    : m_image(image)
{
}

/*!
    Constructs a mip level description suitable for textures with a format that
    does not map to QImage. The floating point or compressed data is specified
    in \a data.
 */
QRhiTextureMipLevel::QRhiTextureMipLevel(const QByteArray &data)
    : m_data(data)
{
}

/*!
    \class QRhiTextureLayer
    \inmodule QtRhi
    \brief Describes one layer (face for cubemaps) in a texture upload operation.
 */

/*!
    Constructs an empty texture layer description.
 */
QRhiTextureLayer::QRhiTextureLayer()
{
}

/*!
    Constructs a texture layer description with the specified list of \a
    mipImages.
 */
QRhiTextureLayer::QRhiTextureLayer(const QVector<QRhiTextureMipLevel> &mipImages)
    : m_mipImages(mipImages)
{
}

/*!
    \class QRhiTextureUploadDescription
    \inmodule QtRhi
    \brief Describes a texture upload operation.

    Used with QRhiResourceUpdateBatch::uploadTexture(). That function has two
    variants: one taking a QImage and one taking a
    QRhiTextureUploadDescription. The former is a convenience version,
    internally creating a QRhiTextureUploadDescription with a single layer and
    a single image in that layer. However, when cubemaps, pre-generated mip
    images, or compressed textures are involved, applications will have to work
    directly with this class instead.

    \note Cubemaps have one layer for each of the six faces in the order +X,
    -X, +Y, -Y, +Z, -Z.

    For example, specifying the faces of a cubemap could look like the following:

    \badcode
        QImage faces[6];
        ...
        QVector<QRhiTextureLayer> layers;
        for (int i = 0; i < 6; ++i)
          layers.append(QRhiTextureLayer({ QRhiTextureMipLevel(faces[i]) });
        QRhiTextureUploadDescription desc(layers);
        resourceUpdates->uploadTexture(texture, desc);
    \endcode

    Another example that specifies mip images for a compressed texture:

    \badcode
        QVector<QRhiTextureMipLevel> mipImages;
        const int mipCount = rhi->mipLevelsForSize(compressedTexture->pixelSize());
        for (int level = 0; level < mipCount; ++level) {
            const QByteArray compressedDataForLevel = ...
            mipImages.append(QRhiTextureMipLevel(compressedDataForLevel));
        }
        QRhiTextureLayer layer(mipImages);
        QRhiTextureUploadDescription desc({ layer });
        resourceUpdates->uploadTexture(compressedTexture, desc);
    \endcode
 */

/*!
    Constructs an empty texture upload description.
 */
QRhiTextureUploadDescription::QRhiTextureUploadDescription()
{
}

/*!
    Constructs a texture upload description with the specified list of \a
    layers.
 */
QRhiTextureUploadDescription::QRhiTextureUploadDescription(const QVector<QRhiTextureLayer> &layers)
    : m_layers(layers)
{
}

/*!
    \class QRhiTextureCopyDescription
    \inmodule QtRhi
    \brief Describes a texture-to-texture copy operation.

    An empty pixelSize() indicates that the entire subresource is to be copied.
    A default constructed copy description therefore leads to copying the
    entire subresource at level 0 of layer 0.

    \note The source texture must be created with
    QRhiTexture::UsedAsTransferSource.

    \note The source and destination rectangles defined by pixelSize(),
    sourceTopLeft(), and destinationTopLeft() must fit the source and
    destination textures, respectively. The behavior is undefined otherwise.
 */

/*!
    Constructs an empty texture copy description.
 */
QRhiTextureCopyDescription::QRhiTextureCopyDescription()
{
}

/*!
    \class QRhiReadbackDescription
    \inmodule QtRhi
    \brief Describes a readback (reading back texture contents from possibly GPU-only memory) operation.

    The source of the readback operation is either a QRhiTexture or the
    current backbuffer of the currently targeted QRhiSwapChain. When
    texture() is not set, the swapchain is used. Otherwise the specified
    QRhiTexture is treated as the source.

    \note Textures used in readbacks must be created with
    QRhiTexture::UsedAsTransferSource.

    \note Swapchains used in readbacks must be created with
    QRhiSwapChain::UsedAsTransferSource.

    layer() and level() are only applicable when the source is a QRhiTexture.

    \note Multisample textures cannot be read back. Readbacks are supported for
    multisample swapchain buffers however.
 */

/*!
    Constructs an empty texture readback description.

    \note The source texture is set to null by default, which is still a valid
    readback: it specifies that the backbuffer of the current swapchain is to
    be read back. (current meaning the frame's target swapchain at the time of
    committing the QRhiResourceUpdateBatch with the
    \l{QRhiResourceUpdateBatch::readBackTexture()}{texture readback} on it)
 */
QRhiReadbackDescription::QRhiReadbackDescription()
{
}

/*!
    Constructs an texture readback description that specifies that level 0 of
    layer 0 of \a texture is to be read back.

    \note \a texture can also be null in which case this constructor is
    identical to the argumentless variant.
 */
QRhiReadbackDescription::QRhiReadbackDescription(QRhiTexture *texture)
    : m_texture(texture)
{
}

/*!
    \class QRhiReadbackResult
    \inmodule QtRhi
    \brief Describes the results of a potentially asynchronous readback operation.

    When \l completed is set, the function is invoked when the \l data is
    available. \l format and \l pixelSize are set upon completion together with
    \l data.
 */

/*!
    \class QRhiNativeHandles
    \inmodule QtRhi
    \brief Base class for classes exposing backend-specific collections of native resource objects.
 */

/*!
    \class QRhiResource
    \inmodule QtRhi
    \brief Base class for classes encapsulating native resource objects.
 */

/*!
    \internal
 */
QRhiResource::QRhiResource(QRhiImplementation *rhi)
    : m_rhi(rhi)
{
    m_id = QRhiGlobalObjectIdGenerator::newId();
}

/*!
   Destructor.
 */
QRhiResource::~QRhiResource()
{
}

/*!
    \fn void QRhiResource::release()

    Releases (or requests defered releasing of) the underlying native graphics
    resources. Safe to call multiple times, subsequent invocations will be a
    no-op then.

    Once release() is called, the QRhiResource instance can be reused, by
    calling the appropriate \c build() function again, or destroyed.

    \note Resources referenced by commands for the current frame should not be
    released until the frame is submitted by QRhi::endFrame().

    \sa releaseAndDestroy(), releaseAndDestroyLater()
 */

/*!
    Releases (or requests defered releasing of) the native graphics resources,
    if there are any, and destroys the QRhiResource. Equivalent to
    \c{r->release(); delete r; }.

    \note Resources referenced by commands for the current frame should not be
    released until the frame is submitted by QRhi::endFrame().

    \sa release(), releaseAndDestroyLater()
 */
void QRhiResource::releaseAndDestroy()
{
    release();
    delete this;
}

/*!
    When called without a frame being recorded, this function is equivalent to
    releaseAndDestroy(). Between a QRhi::beginFrame() and QRhi::endFrame()
    however the behavior is different: the QRhiResource will not be destroyed
    until the frame is submitted via QRhi::endFrame(), thus satisfying the QRhi
    requirement of not altering QRhiResource objects that are referenced by the
    frame being recorded.

    \sa release(), releaseAndDestroy()
 */
void QRhiResource::releaseAndDestroyLater()
{
    m_rhi->addReleaseAndDestroyLater(this);
}

/*!
    \return the currently set object name. By default the name is empty.
 */
QByteArray QRhiResource::name() const
{
    return m_objectName;
}

/*!
    Sets a \a name for the object.

    This has two uses: to get descriptive names for the native graphics
    resources visible in graphics debugging tools, such as
    \l{https://renderdoc.org/}{RenderDoc} and
    \l{https://developer.apple.com/xcode/}{XCode}, and in the output stream of
    QRhiProfiler.

    When it comes to naming native objects by relaying the name via the
    appropriate graphics API, note that the name is ignored when
    QRhi::DebugMarkers are not supported, and may, depending on the backend,
    also be ignored when QRhi::EnableDebugMarkers is not set.

    \note The name may be ignored for objects other than buffers,
    renderbuffers, and textures, depending on the backend.

    \note The name may be modified. For slotted resources, such as a QRhiBuffer
    backed by multiple native buffers, QRhi will append a suffix to make the
    underlying native buffers easily distinguishable from each other.
 */
void QRhiResource::setName(const QByteArray &name)
{