Add some support for primitive restart

src/rhi/qrhi.cpp

@@ -275,12 +275,35 @@ QT_BEGIN_NAMESPACE
     \enum QRhi::Feature
     Flag values to indicate what features are supported by the backend currently in use.
 
-    \value MultisampleTexture Textures with sample count larger than 1 are supported.
-    \value MultisampleRenderBuffer Renderbuffers with sample count larger than 1 are supported.
-    \value DebugMarkers Debug marker groups (and so QRhiCommandBuffer::debugMarkBegin()) are supported.
-    \value Timestamps Command buffer timestamps are supported. Relevant for QRhiProfiler::gpuFrameTimes().
+    \value MultisampleTexture Textures with sample count larger than 1 are
+    supported.
+
+    \value MultisampleRenderBuffer Renderbuffers with sample count larger than
+    1 are supported.
+
+    \value DebugMarkers Debug marker groups (and so
+    QRhiCommandBuffer::debugMarkBegin()) are supported.
+
+    \value Timestamps Command buffer timestamps are supported. Relevant for
+    QRhiProfiler::gpuFrameTimes().
+
     \value Instancing Instanced drawing is supported.
+
     \value CustomInstanceStepRate Instance step rate other than 1 is supported.
+
+    \value PrimitiveRestart Restarting the assembly of primitives when
+    encountering an index value of 0xFFFF
+    (\l{QRhiCommandBuffer::IndexUInt16}{IndexUInt16}) or 0xFFFFFFFF
+    (\l{QRhiCommandBuffer::IndexUInt32}{IndexUInt32}) is always enabled, for
+    certain primitive topologies at least. Due to the wildly varying primitive
+    restart behavior and support in the underlying graphics APIs, primitive
+    restart cannot be controlled with QRhi. Instead, 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}.
  */
 
 /*!

src/rhi/qrhi.h

@@ -1009,7 +1009,8 @@ public:
         DebugMarkers,
         Timestamps,
         Instancing,
-        CustomInstanceStepRate
+        CustomInstanceStepRate,
+        PrimitiveRestart
     };
 
     enum ResourceSizeLimit {

src/rhi/qrhid3d11.cpp

@@ -320,6 +320,8 @@ bool QRhiD3D11::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::CustomInstanceStepRate:
         return true;
+    case QRhi::PrimitiveRestart:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;

src/rhi/qrhigles2.cpp

@@ -323,6 +323,8 @@ bool QRhiGles2::isFeatureSupported(QRhi::Feature feature) const
         return false;
     case QRhi::CustomInstanceStepRate:
         return false;
+    case QRhi::PrimitiveRestart:
+        return false; // say no to madness
     default:
         Q_UNREACHABLE();
         return false;

src/rhi/qrhimetal.mm

@@ -437,6 +437,8 @@ bool QRhiMetal::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::CustomInstanceStepRate:
         return true;
+    case QRhi::PrimitiveRestart:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;

src/rhi/qrhivulkan.cpp

@@ -2863,6 +2863,8 @@ bool QRhiVulkan::isFeatureSupported(QRhi::Feature feature) const
         return true;
     case QRhi::CustomInstanceStepRate:
         return vertexAttribDivisorAvailable;
+    case QRhi::PrimitiveRestart:
+        return true;
     default:
         Q_UNREACHABLE();
         return false;
@@ -4452,6 +4454,7 @@ bool QVkGraphicsPipeline::build()
     memset(&inputAsmInfo, 0, sizeof(inputAsmInfo));
     inputAsmInfo.sType = VK_STRUCTURE_TYPE_PIPELINE_INPUT_ASSEMBLY_STATE_CREATE_INFO;
     inputAsmInfo.topology = toVkTopology(m_topology);
+    inputAsmInfo.primitiveRestartEnable = (m_topology == TriangleStrip || m_topology == LineStrip);
     pipelineInfo.pInputAssemblyState = &inputAsmInfo;
 
     VkPipelineRasterizationStateCreateInfo rastInfo;

todo.txt

 multiwindow_threaded should demo pulling out the device and importing to another rhi
-primitive restart
 advanced blend modes
 gl: tex formats (texture, readback)
 gl: srgb
@@ -21,7 +20,6 @@ gl: ubuf structs, arrays
 test cubemap face as target
 test cubemap face readback
 object names for other than buf/rb/tex
-clang_qdoc ifdefs for q_declare_flags to be removed once qdoc does not choke on them
 
 optional:
 compute?
@@ -48,6 +46,8 @@ dxc for d3d as an alternative to fxc?
 hlsl -> dxc -> spirv -> spirv-cross hmmm...
 
 +++ done
+primitive restart
+fix independent builds
 basic docs
 vk, d3d, mtl: minimize vertex input changes inside passes
 mtl: cbuffers, textures, samplers set should be batched too