From 5349415d126d673b89e98015f0e3a5a98e39520b Mon Sep 17 00:00:00 2001
From: Markus Stange <mstange@themasta.com>
Date: Sun, 25 Aug 2019 17:11:39 +0000
Subject: [PATCH] Bug 1574592 - When rendering into a copy target with
 CompositorOGL, and the window uses native layers for rendering, render into
 an offscreen RenderTarget instead of using a native layer. r=mattwoodrow

On platforms that don't use native layers for rendering, we usually want reftests
to see exactly what's going to end up in the window. It's conceivable that
rendering into offscreen framebuffers might miss bugs on those platforms (though
I'm not sure if we've seen any evidence of this).
But when we're rendering to native layers, we have non-default framebuffers either
way, so we might as well create our own framebuffer rather than asking a native
layer for one. We're not interested in getting this rendering to the screen, so
it's better to leave the native layer out of this.

Differential Revision: https://phabricator.services.mozilla.com/D42406

--HG--
extra : moz-landing-system : lando
---
 gfx/layers/opengl/CompositorOGL.cpp | 26 +++++++++++++++++++++-----
 gfx/layers/opengl/CompositorOGL.h   |  1 +
 2 files changed, 22 insertions(+), 5 deletions(-)

diff --git a/gfx/layers/opengl/CompositorOGL.cpp b/gfx/layers/opengl/CompositorOGL.cpp
index da74a5a70d09..21f691c77698 100644
--- a/gfx/layers/opengl/CompositorOGL.cpp
+++ b/gfx/layers/opengl/CompositorOGL.cpp
@@ -206,6 +206,11 @@ CompositorOGL::CompositorOGL(CompositorBridgeParent* aParent,
       mDestroyed(false),
       mViewportSize(0, 0),
       mCurrentProgram(nullptr) {
+  if (aWidget->GetNativeLayerRoot()) {
+    // We can only render into native layers, our GLContext won't have a usable
+    // default framebuffer.
+    mCanRenderToDefaultFramebuffer = false;
+  }
 #ifdef XP_DARWIN
   TextureSync::RegisterTextureSourceProvider(this);
 #endif
@@ -898,12 +903,24 @@ void CompositorOGL::BeginFrame(const nsIntRegion& aInvalidRegion,
                                  LOCAL_GL_ONE, LOCAL_GL_ONE_MINUS_SRC_ALPHA);
   mGLContext->fEnable(LOCAL_GL_BLEND);
 
-  RefPtr<CompositingRenderTargetOGL> rt =
-      aNativeLayer ? RenderTargetForNativeLayer(aNativeLayer)
-                   : CompositingRenderTargetOGL::RenderTargetForWindow(
-                         this, IntSize(width, height));
+  RefPtr<CompositingRenderTarget> rt;
+  if (mTarget) {
+    if (mCanRenderToDefaultFramebuffer) {
+      rt = CompositingRenderTargetOGL::RenderTargetForWindow(this, rect.Size());
+    } else {
+      rt = CreateRenderTarget(rect, INIT_MODE_CLEAR);
+    }
+  } else if (aNativeLayer) {
+    rt = RenderTargetForNativeLayer(aNativeLayer);
+    mCurrentNativeLayer = aNativeLayer;
+  } else {
+    MOZ_RELEASE_ASSERT(mCanRenderToDefaultFramebuffer);
+    rt = CompositingRenderTargetOGL::RenderTargetForWindow(this, rect.Size());
+  }
+
   if (!rt) {
     *aRenderBoundsOut = IntRect();
+    mCurrentNativeLayer = nullptr;
     return;
   }
 
@@ -912,7 +929,6 @@ void CompositorOGL::BeginFrame(const nsIntRegion& aInvalidRegion,
 
   SetRenderTarget(rt);
   mWindowRenderTarget = mCurrentRenderTarget;
-  mCurrentNativeLayer = aNativeLayer;
 
   if (aClipRectOut && !aClipRectIn) {
     aClipRectOut->SetRect(0, 0, width, height);
diff --git a/gfx/layers/opengl/CompositorOGL.h b/gfx/layers/opengl/CompositorOGL.h
index 0df5daa226f3..2412957be7c7 100644
--- a/gfx/layers/opengl/CompositorOGL.h
+++ b/gfx/layers/opengl/CompositorOGL.h
@@ -302,6 +302,7 @@ class CompositorOGL final : public Compositor {
   RefPtr<GLContext> mGLContext;
   UniquePtr<GLBlitTextureImageHelper> mBlitTextureImageHelper;
   gfx::Matrix4x4 mProjMatrix;
+  bool mCanRenderToDefaultFramebuffer = true;
 
 #ifdef XP_DARWIN
   nsTArray<RefPtr<BufferTextureHost>> mMaybeUnlockBeforeNextComposition;