D3D12: Fix 'ShaderEffect in a ShaderEffectSource as property value'

Import (and clean up) the dropshadow from the shadereffects example.
This is very useful since it tests a lot more paths and cases than
the wobble.

To overcome the issue of not having some of functionality available before
the item is added to a window, make QQuickGenericShaderEffect smarter and
enhance the documentation.

The handling of vertical mirroring is revised. The GLSL and HLSL version of
the dropshadow shaders produce correct, identical output now.

Change-Id: I94800997bfba781140d80720eb6f340cda480747
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 4 insertions, 0 deletions

diff --git a/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp b/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp
index 1fa443abec..62acb8d679 100644
--- a/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp
+++ b/src/plugins/scenegraph/d3d12/qsgd3d12engine.cpp
@@ -1538,6 +1538,10 @@ void QSGD3D12EnginePrivate::finalizePipeline(const QSGD3D12PipelineState &pipeli
         D3D12_ROOT_SIGNATURE_DESC desc;
         desc.NumParameters = rootParamCount;
         desc.pParameters = rootParams;
+        // Mixing up samplers and resource views in QSGD3D12TextureView means
+        // that the number of static samplers has to match the number of
+        // textures. This is not really ideal in general but works for Quick's use cases.
+        // The shaders can still choose to declare and use fewer samplers, if they want to.
         desc.NumStaticSamplers = pipelineState.shaders.rootSig.textureViews.count();
         D3D12_STATIC_SAMPLER_DESC staticSamplers[8];
         int sdIdx = 0;