Bug 1961115 - Skip compositor-related work when rendering without presenting. r=gfx-reviewers,gw

Differential Revision: https://phabricator.services.mozilla.com/D245565

gfx/webrender_bindings/RendererOGL.cpp

@@ -169,6 +169,18 @@ RenderedFrameId RendererOGL::UpdateAndRender(
   widgetContext.mGL = mCompositor->gl();
 #endif
 
+  // If present is false, WebRender needs to render some offscreen content
+  // but we don't want to touch the window, so we avoid most interactions
+  // with mCompositor.
+  bool present = aFrameParams.present;
+
+  LayoutDeviceIntSize size(0, 0);
+  auto bufferAge = 0;
+  bool fullRender = false;
+
+  bool beginFrame = !mThread->IsHandlingDeviceReset();
+
+  if (beginFrame && present) {
     if (!mCompositor->GetWidget()->PreRender(&widgetContext)) {
       // XXX This could cause oom in webrender since pending_texture_updates is
       // not handled. It needs to be addressed.
@@ -176,24 +188,30 @@ RenderedFrameId RendererOGL::UpdateAndRender(
     }
     // XXX set clear color if MOZ_WIDGET_ANDROID is defined.
 
-  if (mThread->IsHandlingDeviceReset() || !mCompositor->BeginFrame()) {
+    if (!mCompositor->BeginFrame()) {
+      beginFrame = false;
+    }
+
+    size = mCompositor->GetBufferSize();
+    bufferAge = mCompositor->GetBufferAge();
+
+    fullRender = mCompositor->RequestFullRender();
+    // When we're rendering to an external target, we want to render everything.
+    if (mCompositor->UsePartialPresent() &&
+        (aReadbackBuffer.isSome() ||
+         layers::ProfilerScreenshots::IsEnabled())) {
+      fullRender = true;
+    }
+  }
+
+  if (!beginFrame) {
     CheckGraphicsResetStatus(gfx::DeviceResetDetectPlace::WR_BEGIN_FRAME,
                              /* aForce */ true);
-    mCompositor->GetWidget()->PostRender(&widgetContext);
     return RenderedFrameId();
   }
 
-  auto size = mCompositor->GetBufferSize();
-  auto bufferAge = mCompositor->GetBufferAge();
-
   wr_renderer_update(mRenderer);
 
-  bool fullRender = mCompositor->RequestFullRender();
-  // When we're rendering to an external target, we want to render everything.
-  if (mCompositor->UsePartialPresent() &&
-      (aReadbackBuffer.isSome() || layers::ProfilerScreenshots::IsEnabled())) {
-    fullRender = true;
-  }
   if (fullRender) {
     wr_renderer_force_redraw(mRenderer);
   }
@@ -203,22 +221,28 @@ RenderedFrameId RendererOGL::UpdateAndRender(
                                      bufferAge, aOutStats, &dirtyRects);
   FlushPipelineInfo();
   if (!rendered) {
+    if (present) {
       mCompositor->CancelFrame();
-    RenderThread::Get()->HandleWebRenderError(WebRenderError::RENDER);
       mCompositor->GetWidget()->PostRender(&widgetContext);
+    }
+    RenderThread::Get()->HandleWebRenderError(WebRenderError::RENDER);
     return RenderedFrameId();
   }
 
+  RenderedFrameId frameId;
+
+  if (present) {
     if (aReadbackBuffer.isSome()) {
       MOZ_ASSERT(aReadbackSize.isSome());
       MOZ_ASSERT(aReadbackFormat.isSome());
-    if (!mCompositor->MaybeReadback(aReadbackSize.ref(), aReadbackFormat.ref(),
+      if (!mCompositor->MaybeReadback(aReadbackSize.ref(),
+                                      aReadbackFormat.ref(),
                                       aReadbackBuffer.ref(), aNeedsYFlip)) {
         wr_renderer_readback(mRenderer, aReadbackSize.ref().width,
                              aReadbackSize.ref().height, aReadbackFormat.ref(),
                              &aReadbackBuffer.ref()[0],
                              aReadbackBuffer.ref().length());
-      if (aNeedsYFlip) {
+        if (aNeedsYFlip != nullptr) {
           *aNeedsYFlip = !mCompositor->SurfaceOriginIsTopLeft();
         }
       }
@@ -230,14 +254,13 @@ RenderedFrameId RendererOGL::UpdateAndRender(
       }
     }
 
-  // Frame recording must happen before EndFrame, as we must ensure we read the
-  // contents of the back buffer before any calls to SwapBuffers which might
-  // invalidate it.
+    // Frame recording must happen before EndFrame, as we must ensure we read
+    // the contents of the back buffer before any calls to SwapBuffers which
+    // might invalidate it.
     MaybeRecordFrame(mLastPipelineInfo);
-
-  RenderedFrameId frameId = mCompositor->EndFrame(dirtyRects);
-
+    frameId = mCompositor->EndFrame(dirtyRects);
     mCompositor->GetWidget()->PostRender(&widgetContext);
+  }
 
 #if defined(ENABLE_FRAME_LATENCY_LOG)
   if (mFrameStartTime) {
@@ -249,9 +272,11 @@ RenderedFrameId RendererOGL::UpdateAndRender(
   mFrameStartTime = TimeStamp();
 #endif
 
+  if (present) {
     if (!mCompositor->MaybeProcessScreenshotQueue()) {
       mScreenshotGrabber.MaybeProcessQueue(this);
     }
+  }
 
   // TODO: Flush pending actions such as texture deletions/unlocks and
   //       textureHosts recycling.

gfx/wr/webrender/src/renderer/mod.rs

@@ -1274,10 +1274,16 @@ impl Renderer {
                     .remove(&doc_id)
                     .unwrap();
 
+                let size = if !device_size.is_empty() {
+                    Some(device_size)
+                } else {
+                    None
+                };
+
                 let result = self.render_impl(
                     doc_id,
                     &mut doc,
-                    Some(device_size),
+                    size,
                     buffer_age,
                 );