mtl: Track attachment usage for tex.rt.

src/rhi/qrhimetal.mm

@@ -1519,6 +1519,17 @@ void QRhiMetal::beginPass(QRhiCommandBuffer *cb,
             cbD->d->currentPassRpDesc.depthAttachment.loadAction = MTLLoadActionLoad;
             cbD->d->currentPassRpDesc.stencilAttachment.loadAction = MTLLoadActionLoad;
         }
+        const QVector<QRhiColorAttachment> colorAttachments = rtTex->m_desc.colorAttachments();
+        for (const QRhiColorAttachment &colorAttachment : colorAttachments) {
+            if (colorAttachment.texture())
+                QRHI_RES(QMetalTexture, colorAttachment.texture())->lastActiveFrameSlot = currentFrameSlot;
+            else if (colorAttachment.renderBuffer())
+                QRHI_RES(QMetalRenderBuffer, colorAttachment.renderBuffer())->lastActiveFrameSlot = currentFrameSlot;
+        }
+        if (rtTex->m_desc.depthStencilBuffer())
+            QRHI_RES(QMetalRenderBuffer, rtTex->m_desc.depthStencilBuffer())->lastActiveFrameSlot = currentFrameSlot;
+        if (rtTex->m_desc.depthTexture())
+            QRHI_RES(QMetalTexture, rtTex->m_desc.depthTexture())->lastActiveFrameSlot = currentFrameSlot;
     }
         break;
     default: