rhi: Execute pending host writes on nativeBuffer() query

Otherwise it is impossible to write an application that pulls out the
VkBuffer for a Dynamic QRhiBuffer, and then uses it with custom Vulkan
operations that read from the buffer. More precisely, the problem arises
only if the buffer in question is not used in combination with any QRhi
operations, because in that case there is nothing that would trigger
doing the host writes queued up by a resource batch's updateDynamicBuffer().

Task-number: QTBUG-82435
Change-Id: Ieb54422f1493921bc6d4d029be56130cd3a1362a
Reviewed-by: Christian Strømme <christian.stromme@qt.io>

1 files changed, 15 insertions, 8 deletions

diff --git a/src/gui/rhi/qrhimetal.mm b/src/gui/rhi/qrhimetal.mm
index 48a562ef1d..314c58b0b7 100644
--- a/src/gui/rhi/qrhimetal.mm
+++ b/src/gui/rhi/qrhimetal.mm
@@ -1827,16 +1827,15 @@ void QRhiMetal::enqueueResourceUpdates(QRhiCommandBuffer *cb, QRhiResourceUpdate
 }
 
 // this handles all types of buffers, not just Dynamic
-void QRhiMetal::executeBufferHostWritesForCurrentFrame(QMetalBuffer *bufD)
+void QRhiMetal::executeBufferHostWritesForSlot(QMetalBuffer *bufD, int slot)
 {
-    const int idx = bufD->d->slotted ? currentFrameSlot : 0;
-    if (bufD->d->pendingUpdates[idx].isEmpty())
+    if (bufD->d->pendingUpdates[slot].isEmpty())
         return;
 
-    void *p = [bufD->d->buf[idx] contents];
+    void *p = [bufD->d->buf[slot] contents];
     int changeBegin = -1;
     int changeEnd = -1;
-    for (const QRhiResourceUpdateBatchPrivate::BufferOp &u : qAsConst(bufD->d->pendingUpdates[idx])) {
+    for (const QRhiResourceUpdateBatchPrivate::BufferOp &u : qAsConst(bufD->d->pendingUpdates[slot])) {
         Q_ASSERT(bufD == QRHI_RES(QMetalBuffer, u.buf));
         memcpy(static_cast<char *>(p) + u.offset, u.data.constData(), size_t(u.data.size()));
         if (changeBegin == -1 || u.offset < changeBegin)
@@ -1846,10 +1845,15 @@ void QRhiMetal::executeBufferHostWritesForCurrentFrame(QMetalBuffer *bufD)
     }
 #ifdef Q_OS_MACOS
     if (changeBegin >= 0 && bufD->d->managed)
-        [bufD->d->buf[idx] didModifyRange: NSMakeRange(NSUInteger(changeBegin), NSUInteger(changeEnd - changeBegin))];
+        [bufD->d->buf[slot] didModifyRange: NSMakeRange(NSUInteger(changeBegin), NSUInteger(changeEnd - changeBegin))];
 #endif
 
-    bufD->d->pendingUpdates[idx].clear();
+    bufD->d->pendingUpdates[slot].clear();
+}
+
+void QRhiMetal::executeBufferHostWritesForCurrentFrame(QMetalBuffer *bufD)
+{
+    executeBufferHostWritesForSlot(bufD, bufD->d->slotted ? currentFrameSlot : 0);
 }
 
 void QRhiMetal::resourceUpdate(QRhiCommandBuffer *cb, QRhiResourceUpdateBatch *resourceUpdates)
@@ -2205,8 +2209,11 @@ QRhiBuffer::NativeBuffer QMetalBuffer::nativeBuffer()
     if (d->slotted) {
         NativeBuffer b;
         Q_ASSERT(sizeof(b.objects) / sizeof(b.objects[0]) >= size_t(QMTL_FRAMES_IN_FLIGHT));
-        for (int i = 0; i < QMTL_FRAMES_IN_FLIGHT; ++i)
+        for (int i = 0; i < QMTL_FRAMES_IN_FLIGHT; ++i) {
+            QRHI_RES_RHI(QRhiMetal);
+            rhiD->executeBufferHostWritesForSlot(this, i);
             b.objects[i] = &d->buf[i];
+        }
         b.slotCount = QMTL_FRAMES_IN_FLIGHT;
         return b;
     }