Add isYUpInNDC()

Complements isYUpInFramebuffer().

src/rhi/qrhi.cpp

@@ -3900,7 +3900,8 @@ QSize QRhi::sizeForMipLevel(int mipLevel, const QSize &baseLevelSize) const
 }
 
 /*!
-    \return \c true if the underlying graphics API has Y up in the framebuffer.
+    \return \c true if the underlying graphics API has the Y axis pointing up
+    in framebuffers and images.
 
     In practice this is \c true for OpenGL only.
  */
@@ -3910,12 +3911,27 @@ bool QRhi::isYUpInFramebuffer() const
 }
 
 /*!
-    \return a matrix that can be used allow applications keep using
-    OpenGL-targeted vertex data and projection matrices (for example, the ones
-    generated by QMatrix4x4::perspective()) regardless of the backed. Once
-    \c{this_matrix * mvp} is used instead of just \c mvp, vertex data with Y up
-    and viewports with depth range 0 - 1 can be used without considering what
-    backend and so graphics API is going to be used at run time.
+    \return \c true if the underlying graphics API has the Y axis pointing up
+    in its normalized device coordinate system.
+
+    In practice this is \c false for Vulkan only.
+
+    \note clipSpaceCorrMatrix() includes the corresponding adjustment (to make
+    Y point up) in its returned matrix.
+ */
+bool QRhi::isYUpInNDC() const
+{
+    return d->isYUpInNDC();
+}
+
+/*!
+    \return a matrix that can be used to allow applications keep using
+    OpenGL-targeted vertex data and perspective projection matrices (such as,
+    the ones generated by QMatrix4x4::perspective()), regardless of the
+    backend. Once \c{this_matrix * mvp} is used instead of just \c mvp, vertex
+    data with Y up and viewports with depth range 0 - 1 can be used without
+    considering what backend and so graphics API is going to be used at run
+    time.
 
     See
     \l{https://matthewwellings.com/blog/the-new-vulkan-coordinate-system/}{this

src/rhi/qrhi.h

@@ -1283,6 +1283,7 @@ public:
     QSize sizeForMipLevel(int mipLevel, const QSize &baseLevelSize) const;
 
     bool isYUpInFramebuffer() const;
+    bool isYUpInNDC() const;
 
     QMatrix4x4 clipSpaceCorrMatrix() const;
 

src/rhi/qrhi_p.h

@@ -131,6 +131,7 @@ public:
     virtual QVector<int> supportedSampleCounts() const = 0;
     virtual int ubufAlignment() const = 0;
     virtual bool isYUpInFramebuffer() const = 0;
+    virtual bool isYUpInNDC() const = 0;
     virtual QMatrix4x4 clipSpaceCorrMatrix() const = 0;
     virtual bool isTextureFormatSupported(QRhiTexture::Format format, QRhiTexture::Flags flags) const = 0;
     virtual bool isFeatureSupported(QRhi::Feature feature) const = 0;

src/rhi/qrhid3d11.cpp

@@ -344,6 +344,11 @@ bool QRhiD3D11::isYUpInFramebuffer() const
     return false;
 }
 
+bool QRhiD3D11::isYUpInNDC() const
+{
+    return true;
+}
+
 QMatrix4x4 QRhiD3D11::clipSpaceCorrMatrix() const
 {
     // Like with Vulkan, but Y is already good.

src/rhi/qrhid3d11_p.h

@@ -520,6 +520,7 @@ public:
     QVector<int> supportedSampleCounts() const override;
     int ubufAlignment() const override;
     bool isYUpInFramebuffer() const override;
+    bool isYUpInNDC() const override;
     QMatrix4x4 clipSpaceCorrMatrix() const override;
     bool isTextureFormatSupported(QRhiTexture::Format format, QRhiTexture::Flags flags) const override;
     bool isFeatureSupported(QRhi::Feature feature) const override;

src/rhi/qrhigles2.cpp

@@ -414,6 +414,11 @@ bool QRhiGles2::isYUpInFramebuffer() const
     return true;
 }
 
+bool QRhiGles2::isYUpInNDC() const
+{
+    return true;
+}
+
 QMatrix4x4 QRhiGles2::clipSpaceCorrMatrix() const
 {
     return QMatrix4x4(); // identity

src/rhi/qrhigles2_p.h

@@ -514,6 +514,7 @@ public:
     QVector<int> supportedSampleCounts() const override;
     int ubufAlignment() const override;
     bool isYUpInFramebuffer() const override;
+    bool isYUpInNDC() const override;
     QMatrix4x4 clipSpaceCorrMatrix() const override;
     bool isTextureFormatSupported(QRhiTexture::Format format, QRhiTexture::Flags flags) const override;
     bool isFeatureSupported(QRhi::Feature feature) const override;

src/rhi/qrhimetal.mm

@@ -455,6 +455,11 @@ bool QRhiMetal::isYUpInFramebuffer() const
     return false;
 }
 
+bool QRhiMetal::isYUpInNDC() const
+{
+    return true;
+}
+
 QMatrix4x4 QRhiMetal::clipSpaceCorrMatrix() const
 {
     // depth range 0..1

src/rhi/qrhimetal_p.h

@@ -346,6 +346,7 @@ public:
     QVector<int> supportedSampleCounts() const override;
     int ubufAlignment() const override;
     bool isYUpInFramebuffer() const override;
+    bool isYUpInNDC() const override;
     QMatrix4x4 clipSpaceCorrMatrix() const override;
     bool isTextureFormatSupported(QRhiTexture::Format format, QRhiTexture::Flags flags) const override;
     bool isFeatureSupported(QRhi::Feature feature) const override;

src/rhi/qrhinull.cpp

@@ -110,6 +110,11 @@ bool QRhiNull::isYUpInFramebuffer() const
     return true;
 }
 
+bool QRhiNull::isYUpInNDC() const
+{
+    return true;
+}
+
 QMatrix4x4 QRhiNull::clipSpaceCorrMatrix() const
 {
     return QMatrix4x4(); // identity

src/rhi/qrhinull_p.h

@@ -233,6 +233,7 @@ public:
     QVector<int> supportedSampleCounts() const override;
     int ubufAlignment() const override;
     bool isYUpInFramebuffer() const override;
+    bool isYUpInNDC() const override;
     QMatrix4x4 clipSpaceCorrMatrix() const override;
     bool isTextureFormatSupported(QRhiTexture::Format format, QRhiTexture::Flags flags) const override;
     bool isFeatureSupported(QRhi::Feature feature) const override;

src/rhi/qrhivulkan.cpp

@@ -2963,9 +2963,14 @@ bool QRhiVulkan::isYUpInFramebuffer() const
     return false;
 }
 
+bool QRhiVulkan::isYUpInNDC() const
+{
+    return false;
+}
+
 QMatrix4x4 QRhiVulkan::clipSpaceCorrMatrix() const
 {
-    // See e.g. https://matthewwellings.com/blog/the-new-vulkan-coordinate-system/
+    // See https://matthewwellings.com/blog/the-new-vulkan-coordinate-system/
 
     static QMatrix4x4 m;
     if (m.isIdentity()) {

src/rhi/qrhivulkan_p.h

@@ -418,6 +418,7 @@ public:
     QVector<int> supportedSampleCounts() const override;
     int ubufAlignment() const override;
     bool isYUpInFramebuffer() const override;
+    bool isYUpInNDC() const override;
     QMatrix4x4 clipSpaceCorrMatrix() const override;
     bool isTextureFormatSupported(QRhiTexture::Format format, QRhiTexture::Flags flags) const override;
     bool isFeatureSupported(QRhi::Feature feature) const override;