rhi: Add explicit subclass for RTs from swapchains

We want to enable gaining access to the underlying resource(s) by
inspecting a QRhiRenderTarget. This is not currently possible for
swapchains since there is nothing that references the actual
QRhiSwapChain. To clean this up, make an explicit, new
QRhiSwapChainRenderTarget subclass. Thus the logic already used in a
couple of places to examine the resources attached to a
QRhiTextureRenderTarget can now work with swapchain render targets too,
by branching based on the resourceType().

This eliminates the somewhat odd setup where a "RenderTarget" resource
is QRhiRenderTarget corresponding (but not exposing!) a swapchain,
whereas a "TextureRenderTarget" is a QRhiTextureRenderTarget which
is a subclass of QRhiRenderTarget. Now we correctly have an (abstract)
base and two subclasses, one for each type of render targets.

Besides, it allows us to clean up the oddly named
Q...ReferenceRenderTarget classes in the backends, which initially tried
to indicate that this "render target" merely references (or, in
practice, is) a swapchain. We can now have a nice and symmetrical
Q...SwapChainRenderTarget and Q...TextureRenderTarget naming scheme.

Change-Id: Ib07e9be99a316eec67b94de0860e08f5f4638959
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 13 insertions, 3 deletions

diff --git a/src/gui/rhi/qrhi_p.h b/src/gui/rhi/qrhi_p.h
index 07f3ad69be..bbc404f09b 100644
--- a/src/gui/rhi/qrhi_p.h
+++ b/src/gui/rhi/qrhi_p.h
@@ -74,6 +74,7 @@ class QRhiSampler;
 class QRhiCommandBuffer;
 class QRhiResourceUpdateBatch;
 class QRhiResourceUpdateBatchPrivate;
+class QRhiSwapChain;
 
 class Q_GUI_EXPORT QRhiDepthStencilClearValue
 {
@@ -697,7 +698,7 @@ public:
         Sampler,
         RenderBuffer,
         RenderPassDescriptor,
-        RenderTarget,
+        SwapChainRenderTarget,
         TextureRenderTarget,
         ShaderResourceBindings,
         GraphicsPipeline,
@@ -1031,8 +1032,6 @@ protected:
 class Q_GUI_EXPORT QRhiRenderTarget : public QRhiResource
 {
 public:
-    QRhiResource::Type resourceType() const override;
-
     virtual QSize pixelSize() const = 0;
     virtual float devicePixelRatio() const = 0;
     virtual int sampleCount() const = 0;
@@ -1045,6 +1044,17 @@ protected:
     QRhiRenderPassDescriptor *m_renderPassDesc = nullptr;
 };
 
+class Q_GUI_EXPORT QRhiSwapChainRenderTarget : public QRhiRenderTarget
+{
+public:
+    QRhiResource::Type resourceType() const override;
+    QRhiSwapChain *swapChain() const { return m_swapchain; }
+
+protected:
+    QRhiSwapChainRenderTarget(QRhiImplementation *rhi, QRhiSwapChain *swapchain_);
+    QRhiSwapChain *m_swapchain;
+};
+
 class Q_GUI_EXPORT QRhiTextureRenderTarget : public QRhiRenderTarget
 {
 public: