QRhi: Allow negative viewport origin

Do not bound viewport rect to surface size, only scirror rect.
Modifying the viewport will move the view origin changing the
way the scene gets rendered.

Pick-to: 6.4
Task-number: QTBUG-106082
Change-Id: I105516bd460af87727d0e73f580b8cf6b748d87f
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

4 files changed, 33 insertions, 22 deletions

diff --git a/src/gui/rhi/qrhi_p_p.h b/src/gui/rhi/qrhi_p_p.h
index 7ac0184a16..446403f9b7 100644
--- a/src/gui/rhi/qrhi_p_p.h
+++ b/src/gui/rhi/qrhi_p_p.h
@@ -245,7 +245,13 @@ private:
     friend class QRhiResourceUpdateBatchPrivate;
 };
 
-template<typename T, size_t N>
+enum QRhiTargetRectBoundMode
+{
+    UnBounded,
+    Bounded
+};
+
+template<QRhiTargetRectBoundMode boundingMode, typename T, size_t N>
 bool qrhi_toTopLeftRenderTargetRect(const QSize &outputSize, const std::array<T, N> &r,
                                     T *x, T *y, T *w, T *h)
 {
@@ -256,7 +262,7 @@ bool qrhi_toTopLeftRenderTargetRect(const QSize &outputSize, const std::array<T,
     // or height. We must handle all other input gracefully, clamping to a zero
     // width or height rect in the worst case, and ensuring the resulting rect
     // is inside the rendertarget's bounds because some APIs' validation/debug
-    // layers are allergic to out of bounds scissor or viewport rects.
+    // layers are allergic to out of bounds scissor rects.
 
     const T outputWidth = outputSize.width();
     const T outputHeight = outputSize.height();
@@ -268,20 +274,23 @@ bool qrhi_toTopLeftRenderTargetRect(const QSize &outputSize, const std::array<T,
 
     *x = r[0];
     *y = outputHeight - (r[1] + inputHeight);
-
-    const T widthOffset = *x < 0 ? -*x : 0;
-    const T heightOffset = *y < 0 ? -*y : 0;
-    *w = *x < outputWidth ? qMax<T>(0, inputWidth - widthOffset) : 0;
-    *h = *y < outputHeight ? qMax<T>(0, inputHeight - heightOffset) : 0;
-
-    *x = qBound<T>(0, *x, outputWidth - 1);
-    *y = qBound<T>(0, *y, outputHeight - 1);
-
-    if (*x + *w > outputWidth)
-        *w = qMax<T>(0, outputWidth - *x);
-    if (*y + *h > outputHeight)
-        *h = qMax<T>(0, outputHeight - *y);
-
+    *w = inputWidth;
+    *h = inputHeight;
+
+    if (boundingMode == Bounded) {
+        const T widthOffset = *x < 0 ? -*x : 0;
+        const T heightOffset = *y < 0 ? -*y : 0;
+        *w = *x < outputWidth ? qMax<T>(0, inputWidth - widthOffset) : 0;
+        *h = *y < outputHeight ? qMax<T>(0, inputHeight - heightOffset) : 0;
+
+        *x = qBound<T>(0, *x, outputWidth - 1);
+        *y = qBound<T>(0, *y, outputHeight - 1);
+
+        if (*x + *w > outputWidth)
+            *w = qMax<T>(0, outputWidth - *x);
+        if (*y + *h > outputHeight)
+            *h = qMax<T>(0, outputHeight - *y);
+    }
     return true;
 }
 
diff --git a/src/gui/rhi/qrhid3d11.cpp b/src/gui/rhi/qrhid3d11.cpp
index 3ef1fa394e..da7089edf9 100644
--- a/src/gui/rhi/qrhid3d11.cpp
+++ b/src/gui/rhi/qrhid3d11.cpp
@@ -1084,7 +1084,7 @@ void QRhiD3D11::setViewport(QRhiCommandBuffer *cb, const QRhiViewport &viewport)
 
     // d3d expects top-left, QRhiViewport is bottom-left
     float x, y, w, h;
-    if (!qrhi_toTopLeftRenderTargetRect(outputSize, viewport.viewport(), &x, &y, &w, &h))
+    if (!qrhi_toTopLeftRenderTargetRect<UnBounded>(outputSize, viewport.viewport(), &x, &y, &w, &h))
         return;
 
     QD3D11CommandBuffer::Command &cmd(cbD->commands.get());
@@ -1106,7 +1106,7 @@ void QRhiD3D11::setScissor(QRhiCommandBuffer *cb, const QRhiScissor &scissor)
 
     // d3d expects top-left, QRhiScissor is bottom-left
     int x, y, w, h;
-    if (!qrhi_toTopLeftRenderTargetRect(outputSize, scissor.scissor(), &x, &y, &w, &h))
+    if (!qrhi_toTopLeftRenderTargetRect<Bounded>(outputSize, scissor.scissor(), &x, &y, &w, &h))
         return;
 
     QD3D11CommandBuffer::Command &cmd(cbD->commands.get());
diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index 31364761a2..5b18ff3e96 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -1643,7 +1643,7 @@ void QRhiMetal::setViewport(QRhiCommandBuffer *cb, const QRhiViewport &viewport)
 
     // x,y is top-left in MTLViewportRect but bottom-left in QRhiViewport
     float x, y, w, h;
-    if (!qrhi_toTopLeftRenderTargetRect(outputSize, viewport.viewport(), &x, &y, &w, &h))
+    if (!qrhi_toTopLeftRenderTargetRect<UnBounded>(outputSize, viewport.viewport(), &x, &y, &w, &h))
         return;
 
     MTLViewport vp;
@@ -1659,6 +1659,7 @@ void QRhiMetal::setViewport(QRhiCommandBuffer *cb, const QRhiViewport &viewport)
     if (cbD->currentGraphicsPipeline
         && !cbD->currentGraphicsPipeline->m_flags.testFlag(QRhiGraphicsPipeline::UsesScissor)) {
         MTLScissorRect s;
+        qrhi_toTopLeftRenderTargetRect<Bounded>(outputSize, viewport.viewport(), &x, &y, &w, &h);
         s.x = NSUInteger(x);
         s.y = NSUInteger(y);
         s.width = NSUInteger(w);
@@ -1676,7 +1677,7 @@ void QRhiMetal::setScissor(QRhiCommandBuffer *cb, const QRhiScissor &scissor)
 
     // x,y is top-left in MTLScissorRect but bottom-left in QRhiScissor
     int x, y, w, h;
-    if (!qrhi_toTopLeftRenderTargetRect(outputSize, scissor.scissor(), &x, &y, &w, &h))
+    if (!qrhi_toTopLeftRenderTargetRect<Bounded>(outputSize, scissor.scissor(), &x, &y, &w, &h))
         return;
 
     MTLScissorRect s;
diff --git a/src/gui/rhi/qrhivulkan.cpp b/src/gui/rhi/qrhivulkan.cpp
index 05a67e82de..832db33631 100644
--- a/src/gui/rhi/qrhivulkan.cpp
+++ b/src/gui/rhi/qrhivulkan.cpp
@@ -4927,7 +4927,7 @@ void QRhiVulkan::setViewport(QRhiCommandBuffer *cb, const QRhiViewport &viewport
 
     // x,y is top-left in VkViewport but bottom-left in QRhiViewport
     float x, y, w, h;
-    if (!qrhi_toTopLeftRenderTargetRect(outputSize, viewport.viewport(), &x, &y, &w, &h))
+    if (!qrhi_toTopLeftRenderTargetRect<UnBounded>(outputSize, viewport.viewport(), &x, &y, &w, &h))
         return;
 
     QVkCommandBuffer::Command &cmd(cbD->commands.get());
@@ -4951,6 +4951,7 @@ void QRhiVulkan::setViewport(QRhiCommandBuffer *cb, const QRhiViewport &viewport
                     ->m_flags.testFlag(QRhiGraphicsPipeline::UsesScissor)) {
         QVkCommandBuffer::Command &cmd(cbD->commands.get());
         VkRect2D *s = &cmd.args.setScissor.scissor;
+        qrhi_toTopLeftRenderTargetRect<Bounded>(outputSize, viewport.viewport(), &x, &y, &w, &h);
         s->offset.x = int32_t(x);
         s->offset.y = int32_t(y);
         s->extent.width = uint32_t(w);
@@ -4973,7 +4974,7 @@ void QRhiVulkan::setScissor(QRhiCommandBuffer *cb, const QRhiScissor &scissor)
 
     // x,y is top-left in VkRect2D but bottom-left in QRhiScissor
     int x, y, w, h;
-    if (!qrhi_toTopLeftRenderTargetRect(outputSize, scissor.scissor(), &x, &y, &w, &h))
+    if (!qrhi_toTopLeftRenderTargetRect<Bounded>(outputSize, scissor.scissor(), &x, &y, &w, &h))
         return;
 
     QVkCommandBuffer::Command &cmd(cbD->commands.get());