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>

11 files changed, 162 insertions, 2 deletions

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index 952183f55e..70525689e9 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -330,9 +330,22 @@ Q_LOGGING_CATEGORY(QRHI_LOG_INFO, "qt.rhi.general")
         ubuf->setSize(512);
         ubuf->create(); // same as ubuf->destroy(); ubuf->create();
 
-        // that's it, srb needs no changes whatsoever
+        // That's it, srb needs no changes whatsoever, any references in it to
+        // ubuf stay valid. When it comes to internal details, such as that
+        // ubuf may now be backed by a completely different native buffer
+        // resource, that is is recognized and handled automatically by the
+        // next setShaderResources().
     \endcode
 
+    QRhiTextureRenderTarget offers the same contract: calling
+    QRhiCommandBuffer::beginPass() is safe even when one of the render target's
+    associated textures or renderbuffers has been rebuilt (by calling \c
+    create() on it) since the creation of the render target object. This allows
+    the application to resize a texture by setting a new pixel size on the
+    QRhiTexture and calling create(), thus creating a whole new native texture
+    resource underneath, without having to update the QRhiTextureRenderTarget
+    as that will be done implicitly in beginPass().
+
     \section3 Pooled objects
 
     In addition to resources, there are pooled objects as well, such as,
@@ -5669,6 +5682,25 @@ void QRhiCommandBuffer::resourceUpdate(QRhiResourceUpdateBatch *resourceUpdates)
     called inside a pass. Also, with the exception of setGraphicsPipeline(),
     they expect to have a pipeline set already on the command buffer.
     Unspecified issues may arise otherwise, depending on the backend.
+
+    If \a rt is a QRhiTextureRenderTarget, beginPass() performs a check to see
+    if the texture and renderbuffer objects referenced from the render target
+    are up-to-date. This is similar to what setShaderResources() does for
+    QRhiShaderResourceBindings. If any of the attachments had been rebuilt
+    since QRhiTextureRenderTarget::create(), an implicit call to create() is
+    made on \a rt. Therefore, if \a rt has a QRhiTexture color attachment \c
+    texture, and one needs to make the texture a different size, the following
+    is then valid:
+    \badcode
+      rt = rhi->newTextureRenderTarget({ { texture } });
+      rt->create();
+      ...
+      texture->setPixelSize(new_size);
+      texture->create();
+      cb->beginPass(rt, ...); // this is ok, no explicit rt->create() is required before
+    \endcode
+
+    \sa endPass()
  */
 void QRhiCommandBuffer::beginPass(QRhiRenderTarget *rt,
                                   const QColor &colorClearValue,
@@ -5684,6 +5716,8 @@ void QRhiCommandBuffer::beginPass(QRhiRenderTarget *rt,
 
     \a resourceUpdates, when not null, specifies a resource update batch that
     is to be committed and then released.
+
+    \sa beginPass()
  */
 void QRhiCommandBuffer::endPass(QRhiResourceUpdateBatch *resourceUpdates)
 {
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
diff --git a/src/gui/rhi/qrhid3d11.cpp b/src/gui/rhi/qrhid3d11.cpp
index f6076bc800..a8fd9a686f 100644
--- a/src/gui/rhi/qrhid3d11.cpp
+++ b/src/gui/rhi/qrhid3d11.cpp
@@ -1762,6 +1762,8 @@ void QRhiD3D11::beginPass(QRhiCommandBuffer *cb,
         QD3D11TextureRenderTarget *rtTex = QRHI_RES(QD3D11TextureRenderTarget, rt);
         wantsColorClear = !rtTex->m_flags.testFlag(QRhiTextureRenderTarget::PreserveColorContents);
         wantsDsClear = !rtTex->m_flags.testFlag(QRhiTextureRenderTarget::PreserveDepthStencilContents);
+        if (!QRhiRenderTargetAttachmentTracker::isUpToDate<QD3D11Texture, QD3D11RenderBuffer>(rtTex->description(), rtD->currentResIdList))
+            rtTex->create();
     }
 
     cbD->commands.get().cmd = QD3D11CommandBuffer::Command::ResetShaderResources;
@@ -2898,6 +2900,7 @@ bool QD3D11RenderBuffer::create()
     QRHI_PROF;
     QRHI_PROF_F(newRenderBuffer(this, false, false, int(sampleDesc.Count)));
 
+    generation += 1;
     rhiD->registerResource(this);
     return true;
 }
@@ -3609,6 +3612,8 @@ bool QD3D11TextureRenderTarget::create()
     d.dsv = dsv;
     d.rp = QRHI_RES(QD3D11RenderPassDescriptor, m_renderPassDesc);
 
+    QRhiRenderTargetAttachmentTracker::updateResIdList<QD3D11Texture, QD3D11RenderBuffer>(m_desc, &d.currentResIdList);
+
     rhiD->registerResource(this);
     return true;
 }
diff --git a/src/gui/rhi/qrhid3d11_p_p.h b/src/gui/rhi/qrhid3d11_p_p.h
index 3a333fe8a7..70c7ad969b 100644
--- a/src/gui/rhi/qrhid3d11_p_p.h
+++ b/src/gui/rhi/qrhid3d11_p_p.h
@@ -96,6 +96,7 @@ struct QD3D11RenderBuffer : public QRhiRenderBuffer
     ID3D11RenderTargetView *rtv = nullptr;
     DXGI_FORMAT dxgiFormat;
     DXGI_SAMPLE_DESC sampleDesc;
+    uint generation = 0;
     friend class QRhiD3D11;
 };
 
@@ -172,6 +173,8 @@ struct QD3D11RenderTargetData
     static const int MAX_COLOR_ATTACHMENTS = 8;
     ID3D11RenderTargetView *rtv[MAX_COLOR_ATTACHMENTS];
     ID3D11DepthStencilView *dsv = nullptr;
+
+    QRhiRenderTargetAttachmentTracker::ResIdList currentResIdList;
 };
 
 struct QD3D11ReferenceRenderTarget : public QRhiRenderTarget
diff --git a/src/gui/rhi/qrhigles2.cpp b/src/gui/rhi/qrhigles2.cpp
index f0b97ce36a..67d08d3042 100644
--- a/src/gui/rhi/qrhigles2.cpp
+++ b/src/gui/rhi/qrhigles2.cpp
@@ -3793,6 +3793,12 @@ void QRhiGles2::beginPass(QRhiCommandBuffer *cb,
     // glMemoryBarrier() calls based on that tracker when submitted.
     enqueueBarriersForPass(cbD);
 
+    if (rt->resourceType() == QRhiRenderTarget::TextureRenderTarget) {
+        QGles2TextureRenderTarget *rtTex = QRHI_RES(QGles2TextureRenderTarget, rt);
+        if (!QRhiRenderTargetAttachmentTracker::isUpToDate<QGles2Texture, QGles2RenderBuffer>(rtTex->description(), rtTex->d.currentResIdList))
+            rtTex->create();
+    }
+
     bool wantsColorClear, wantsDsClear;
     QGles2RenderTargetData *rtD = enqueueBindFramebuffer(rt, cbD, &wantsColorClear, &wantsDsClear);
 
@@ -4626,6 +4632,7 @@ bool QGles2RenderBuffer::create()
     }
 
     owns = true;
+    generation += 1;
     rhiD->registerResource(this);
     return true;
 }
@@ -4653,6 +4660,7 @@ bool QGles2RenderBuffer::createFrom(NativeRenderBuffer src)
     QRHI_PROF_F(newRenderBuffer(this, false, false, samples));
 
     owns = false;
+    generation += 1;
     rhiD->registerResource(this);
     return true;
 }
@@ -5114,6 +5122,8 @@ bool QGles2TextureRenderTarget::create()
         return false;
     }
 
+    QRhiRenderTargetAttachmentTracker::updateResIdList<QGles2Texture, QGles2RenderBuffer>(m_desc, &d.currentResIdList);
+
     rhiD->registerResource(this);
     return true;
 }
diff --git a/src/gui/rhi/qrhigles2_p_p.h b/src/gui/rhi/qrhigles2_p_p.h
index 6ee6af8fc5..c0f3883002 100644
--- a/src/gui/rhi/qrhigles2_p_p.h
+++ b/src/gui/rhi/qrhigles2_p_p.h
@@ -108,6 +108,7 @@ struct QGles2RenderBuffer : public QRhiRenderBuffer
     GLuint stencilRenderbuffer = 0; // when packed depth-stencil not supported
     int samples;
     bool owns = true;
+    uint generation = 0;
     friend class QRhiGles2;
 };
 
@@ -213,6 +214,7 @@ struct QGles2RenderTargetData
     int colorAttCount = 0;
     int dsAttCount = 0;
     bool srgbUpdateAndBlend = false;
+    QRhiRenderTargetAttachmentTracker::ResIdList currentResIdList;
 };
 
 struct QGles2ReferenceRenderTarget : public QRhiRenderTarget
diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index 5219b5c71d..626eac433b 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -296,6 +296,8 @@ struct QMetalRenderTargetData
         bool hasStencil = false;
         bool depthNeedsStore = false;
     } fb;
+
+    QRhiRenderTargetAttachmentTracker::ResIdList currentResIdList;
 };
 
 struct QMetalGraphicsPipelineData
@@ -2030,6 +2032,8 @@ void QRhiMetal::beginPass(QRhiCommandBuffer *cb,
     {
         QMetalTextureRenderTarget *rtTex = QRHI_RES(QMetalTextureRenderTarget, rt);
         rtD = rtTex->d;
+        if (!QRhiRenderTargetAttachmentTracker::isUpToDate<QMetalTexture, QMetalRenderBuffer>(rtTex->description(), rtD->currentResIdList))
+            rtTex->create();
         cbD->d->currentPassRpDesc = d->createDefaultRenderPass(rtD->dsAttCount, colorClearValue, depthStencilClearValue, rtD->colorAttCount);
         if (rtTex->m_flags.testFlag(QRhiTextureRenderTarget::PreserveColorContents)) {
             for (uint i = 0; i < uint(rtD->colorAttCount); ++i)
@@ -3181,6 +3185,8 @@ bool QMetalTextureRenderTarget::create()
         d->dsAttCount = 0;
     }
 
+    QRhiRenderTargetAttachmentTracker::updateResIdList<QMetalTexture, QMetalRenderBuffer>(m_desc, &d->currentResIdList);
+
     return true;
 }
 
diff --git a/src/gui/rhi/qrhinull.cpp b/src/gui/rhi/qrhinull.cpp
index b23af75bd9..6e85e02cc2 100644
--- a/src/gui/rhi/qrhinull.cpp
+++ b/src/gui/rhi/qrhinull.cpp
@@ -553,12 +553,18 @@ void QRhiNull::beginPass(QRhiCommandBuffer *cb,
                          QRhiResourceUpdateBatch *resourceUpdates,
                          QRhiCommandBuffer::BeginPassFlags flags)
 {
-    Q_UNUSED(rt);
     Q_UNUSED(colorClearValue);
     Q_UNUSED(depthStencilClearValue);
     Q_UNUSED(flags);
+
     if (resourceUpdates)
         resourceUpdate(cb, resourceUpdates);
+
+    if (rt->resourceType() == QRhiRenderTarget::TextureRenderTarget) {
+        QNullTextureRenderTarget *rtTex = QRHI_RES(QNullTextureRenderTarget, rt);
+        if (!QRhiRenderTargetAttachmentTracker::isUpToDate<QNullTexture, QNullRenderBuffer>(rtTex->description(), rtTex->d.currentResIdList))
+            rtTex->create();
+    }
 }
 
 void QRhiNull::endPass(QRhiCommandBuffer *cb, QRhiResourceUpdateBatch *resourceUpdates)
@@ -660,6 +666,7 @@ bool QNullRenderBuffer::create()
         destroy();
 
     valid = true;
+    generation += 1;
 
     QRHI_PROF;
     QRHI_PROF_F(newRenderBuffer(this, false, false, 1));
@@ -726,6 +733,8 @@ bool QNullTexture::create()
         }
     }
 
+    generation += 1;
+
     QRHI_PROF;
     QRHI_PROF_F(newTexture(this, true, mipLevelCount, layerCount, 1));
     rhiD->registerResource(this);
@@ -748,6 +757,8 @@ bool QNullTexture::createFrom(QRhiTexture::NativeTexture src)
     QSize size = m_pixelSize.isEmpty() ? QSize(1, 1) : m_pixelSize;
     const int mipLevelCount = hasMipMaps ? rhiD->q->mipLevelsForSize(size) : 1;
 
+    generation += 1;
+
     QRHI_PROF;
     QRHI_PROF_F(newTexture(this, false, mipLevelCount, isCube ? 6 : (isArray ? m_arraySize : 1), 1));
     rhiD->registerResource(this);
@@ -871,6 +882,7 @@ bool QNullTextureRenderTarget::create()
     } else if (m_desc.depthTexture()) {
         d.pixelSize = m_desc.depthTexture()->pixelSize();
     }
+    QRhiRenderTargetAttachmentTracker::updateResIdList<QNullTexture, QNullRenderBuffer>(m_desc, &d.currentResIdList);
     return true;
 }
 
diff --git a/src/gui/rhi/qrhinull_p_p.h b/src/gui/rhi/qrhinull_p_p.h
index 4d3c508044..217ec8ef39 100644
--- a/src/gui/rhi/qrhinull_p_p.h
+++ b/src/gui/rhi/qrhinull_p_p.h
@@ -78,6 +78,7 @@ struct QNullRenderBuffer : public QRhiRenderBuffer
     QRhiTexture::Format backingFormat() const override;
 
     bool valid = false;
+    uint generation = 0;
 };
 
 struct QNullTexture : public QRhiTexture
@@ -91,6 +92,7 @@ struct QNullTexture : public QRhiTexture
 
     bool valid = false;
     QVarLengthArray<std::array<QImage, QRhi::MAX_MIP_LEVELS>, 6> image;
+    uint generation = 0;
 };
 
 struct QNullSampler : public QRhiSampler
@@ -119,6 +121,7 @@ struct QNullRenderTargetData
     QNullRenderPassDescriptor *rp = nullptr;
     QSize pixelSize;
     float dpr = 1;
+    QRhiRenderTargetAttachmentTracker::ResIdList currentResIdList;
 };
 
 struct QNullReferenceRenderTarget : public QRhiRenderTarget
diff --git a/src/gui/rhi/qrhivulkan.cpp b/src/gui/rhi/qrhivulkan.cpp
index 03f3fb4ad8..e23900069c 100644
--- a/src/gui/rhi/qrhivulkan.cpp
+++ b/src/gui/rhi/qrhivulkan.cpp
@@ -2175,6 +2175,9 @@ static inline QRhiPassResourceTracker::UsageState toPassTrackerUsageState(const
 
 void QRhiVulkan::activateTextureRenderTarget(QVkCommandBuffer *cbD, QVkTextureRenderTarget *rtD)
 {
+    if (!QRhiRenderTargetAttachmentTracker::isUpToDate<QVkTexture, QVkRenderBuffer>(rtD->description(), rtD->d.currentResIdList))
+        rtD->create();
+
     rtD->lastActiveFrameSlot = currentFrameSlot;
     rtD->d.rp->lastActiveFrameSlot = currentFrameSlot;
     QRhiPassResourceTracker &passResTracker(cbD->passResTrackers[cbD->currentPassResTrackerIndex]);
@@ -5759,6 +5762,7 @@ bool QVkRenderBuffer::create()
     }
 
     lastActiveFrameSlot = -1;
+    generation += 1;
     rhiD->registerResource(this);
     return true;
 }
@@ -6572,6 +6576,8 @@ bool QVkTextureRenderTarget::create()
         return false;
     }
 
+    QRhiRenderTargetAttachmentTracker::updateResIdList<QVkTexture, QVkRenderBuffer>(m_desc, &d.currentResIdList);
+
     lastActiveFrameSlot = -1;
     rhiD->registerResource(this);
     return true;
diff --git a/src/gui/rhi/qrhivulkan_p_p.h b/src/gui/rhi/qrhivulkan_p_p.h
index 42ae9aef3b..da69a0d70d 100644
--- a/src/gui/rhi/qrhivulkan_p_p.h
+++ b/src/gui/rhi/qrhivulkan_p_p.h
@@ -123,6 +123,7 @@ struct QVkRenderBuffer : public QRhiRenderBuffer
     QVkTexture *backingTexture = nullptr;
     VkFormat vkformat;
     int lastActiveFrameSlot = -1;
+    uint generation = 0;
     friend class QRhiVulkan;
 };
 
@@ -214,6 +215,7 @@ struct QVkRenderTargetData
     int colorAttCount = 0;
     int dsAttCount = 0;
     int resolveAttCount = 0;
+    QRhiRenderTargetAttachmentTracker::ResIdList currentResIdList;
     static const int MAX_COLOR_ATTACHMENTS = 8;
 };