mtl: Make sure depth is written out when using a depth texture

As we assume the texture will then be sampled afterwards so a store
action of DontCare is potentially wrong.

src/rhi/qrhimetal.mm

@@ -247,6 +247,7 @@ struct QMetalRenderTargetData
         ColorAtt colorAtt[QMetalRenderPassDescriptor::MAX_COLOR_ATTACHMENTS];
         id<MTLTexture> dsTex = nil;
         bool hasStencil = false;
+        bool depthNeedsStore = false;
     } fb;
 };
 
@@ -1011,6 +1012,7 @@ QRhi::FrameOpResult QRhiMetal::beginFrame(QRhiSwapChain *swapChain, QRhi::BeginF
     swapChainD->rtWrapper.d->fb.colorAtt[0] = colorAtt;
     swapChainD->rtWrapper.d->fb.dsTex = swapChainD->ds ? swapChainD->ds->d->tex : nil;
     swapChainD->rtWrapper.d->fb.hasStencil = swapChainD->ds ? true : false;
+    swapChainD->rtWrapper.d->fb.depthNeedsStore = false;
 
     QRhiProfilerPrivate *rhiP = profilerPrivateOrNull();
     QRHI_PROF_F(beginSwapChainFrame(swapChain));
@@ -1572,6 +1574,8 @@ void QRhiMetal::beginPass(QRhiCommandBuffer *cb,
         Q_ASSERT(rtD->fb.dsTex);
         cbD->d->currentPassRpDesc.depthAttachment.texture = rtD->fb.dsTex;
         cbD->d->currentPassRpDesc.stencilAttachment.texture = rtD->fb.hasStencil ? rtD->fb.dsTex : nil;
+        if (rtD->fb.depthNeedsStore) // Depth/Stencil is set to DontCare by default, override if  needed
+            cbD->d->currentPassRpDesc.depthAttachment.storeAction = MTLStoreActionStore;
     }
 
     cbD->d->currentPassEncoder = [cbD->d->cb renderCommandEncoderWithDescriptor: cbD->d->currentPassRpDesc];
@@ -2374,6 +2378,7 @@ bool QMetalTextureRenderTarget::build()
             QMetalTexture *depthTexD = QRHI_RES(QMetalTexture, m_desc.depthTexture());
             d->fb.dsTex = depthTexD->d->tex;
             d->fb.hasStencil = false;
+            d->fb.depthNeedsStore = true;
             if (d->colorAttCount == 0) {
                 d->pixelSize = depthTexD->pixelSize();
                 d->sampleCount = depthTexD->samples;
@@ -2382,6 +2387,7 @@ bool QMetalTextureRenderTarget::build()
             QMetalRenderBuffer *depthRbD = QRHI_RES(QMetalRenderBuffer, m_desc.depthStencilBuffer());
             d->fb.dsTex = depthRbD->d->tex;
             d->fb.hasStencil = true;
+            d->fb.depthNeedsStore = false;
             if (d->colorAttCount == 0) {
                 d->pixelSize = depthRbD->pixelSize();
                 d->sampleCount = depthRbD->samples;