rhi: Auto-rebuild rt by tracking attachment id and generation

Unlike the shader resource binding lists that automatically recognize
in setShaderResources() when a referenced QRhiResource has been rebuilt
in the meantime (create() was called i.e. there may be completely
different native objects underneath), QRhiTextureRenderTarget has no
such thing. This leads to an asymmetric API and requires also rebuilding
the rt whenever an attachment is rebuilt:

rt = rhi->newTextureRenderTarget({ { texture } })
rt->create()
cb->beginPass(rt, ...)
texture->setPixelSize(...)
texture->create()
rt->create() // this should not be needed
cb->beginPass(rt, ...)

Avoid having to do that second rt->create().

Change-Id: If14eaa7aac3530950498bbdf834324d0741a7c4d
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

1 files changed, 77 insertions, 0 deletions

diff --git a/src/gui/rhi/qrhi_p_p.h b/src/gui/rhi/qrhi_p_p.h
index 7a3f94846d..9e8a3a846f 100644
--- a/src/gui/rhi/qrhi_p_p.h
+++ b/src/gui/rhi/qrhi_p_p.h
@@ -706,6 +706,83 @@ private:
     int p = 0;
 };
 
+struct QRhiRenderTargetAttachmentTracker
+{
+    struct ResId { quint64 id; uint generation; };
+    using ResIdList = QVarLengthArray<ResId, 8 * 2 + 1>; // color, resolve, ds
+
+    template<typename TexType, typename RenderBufferType>
+    static void updateResIdList(const QRhiTextureRenderTargetDescription &desc, ResIdList *dst);
+
+    template<typename TexType, typename RenderBufferType>
+    static bool isUpToDate(const QRhiTextureRenderTargetDescription &desc, const ResIdList &currentResIdList);
+};
+
+inline bool operator==(const QRhiRenderTargetAttachmentTracker::ResId &a, const QRhiRenderTargetAttachmentTracker::ResId &b)
+{
+    return a.id == b.id && a.generation == b.generation;
+}
+
+inline bool operator!=(const QRhiRenderTargetAttachmentTracker::ResId &a, const QRhiRenderTargetAttachmentTracker::ResId &b)
+{
+    return !(a == b);
+}
+
+template<typename TexType, typename RenderBufferType>
+void QRhiRenderTargetAttachmentTracker::updateResIdList(const QRhiTextureRenderTargetDescription &desc, ResIdList *dst)
+{
+    const quintptr colorAttCount = desc.cendColorAttachments() - desc.cbeginColorAttachments();
+    const bool hasDepthStencil = desc.depthStencilBuffer() || desc.depthTexture();
+    dst->resize(colorAttCount * 2 + (hasDepthStencil ? 1 : 0));
+    int n = 0;
+    for (auto it = desc.cbeginColorAttachments(), itEnd = desc.cendColorAttachments(); it != itEnd; ++it, ++n) {
+        const QRhiColorAttachment &colorAtt(*it);
+        if (colorAtt.texture()) {
+            TexType *texD = QRHI_RES(TexType, colorAtt.texture());
+            (*dst)[n] = { texD->globalResourceId(), texD->generation };
+        } else if (colorAtt.renderBuffer()) {
+            RenderBufferType *rbD = QRHI_RES(RenderBufferType, colorAtt.renderBuffer());
+            (*dst)[n] = { rbD->globalResourceId(), rbD->generation };
+        } else {
+            (*dst)[n] = { 0, 0 };
+        }
+        ++n;
+        if (colorAtt.resolveTexture()) {
+            TexType *texD = QRHI_RES(TexType, colorAtt.resolveTexture());
+            (*dst)[n] = { texD->globalResourceId(), texD->generation };
+        } else {
+            (*dst)[n] = { 0, 0 };
+        }
+    }
+    if (hasDepthStencil) {
+        if (desc.depthTexture()) {
+            TexType *depthTexD = QRHI_RES(TexType, desc.depthTexture());
+            (*dst)[n] = { depthTexD->globalResourceId(), depthTexD->generation };
+        } else if (desc.depthStencilBuffer()) {
+            RenderBufferType *depthRbD = QRHI_RES(RenderBufferType, desc.depthStencilBuffer());
+            (*dst)[n] = { depthRbD->globalResourceId(), depthRbD->generation };
+        } else {
+            (*dst)[n] = { 0, 0 };
+        }
+    }
+}
+
+template<typename TexType, typename RenderBufferType>
+bool QRhiRenderTargetAttachmentTracker::isUpToDate(const QRhiTextureRenderTargetDescription &desc, const ResIdList &currentResIdList)
+{
+    // Just as setShaderResources() recognizes if an srb's referenced
+    // resources have been rebuilt (got a create() since the srb's
+    // create()), we should do the same for the textures and renderbuffers
+    // referenced from the rendertarget. It is not uncommon that a texture
+    // or ds buffer gets resized due to following a window size in some
+    // form, which involves a create() on them. It is then nice if the
+    // render target auto-rebuilds in beginPass().
+
+    ResIdList resIdList;
+    updateResIdList<TexType, RenderBufferType>(desc, &resIdList);
+    return resIdList == currentResIdList;
+}
+
 QT_END_NAMESPACE
 
 #endif