Bug 1548484 - respect Cairo blit size limits when using BasicComposit…

…or. r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D30571

--HG--
extra : moz-landing-system : lando

gfx/2d/DrawTargetCairo.h

@@ -174,7 +174,7 @@ class DrawTargetCairo final : public DrawTarget {
   static cairo_surface_t* GetDummySurface();
 
   // Cairo hardcodes this as its maximum surface size.
-  static size_t GetMaxSurfaceSize() { return 32767; }
+  static size_t GetMaxSurfaceSize() { return 32766; }
 
  private:  // methods
   // Init cairo surface without doing a cairo_surface_reference() call.

gfx/layers/basic/BasicCompositor.cpp

@@ -218,7 +218,14 @@ BasicCompositor::BasicCompositor(CompositorBridgeParent* aParent,
       mFullWindowRenderTarget(nullptr) {
   MOZ_COUNT_CTOR(BasicCompositor);
 
-  mMaxTextureSize = Factory::GetMaxSurfaceSize(gfxVars::ContentBackend());
+  // The widget backends may create intermediate Cairo surfaces to deal with
+  // various window buffers, regardless of actual content backend type, when
+  // using the basic compositor. Ensure that the buffers will be able to fit
+  // in or blit with a Cairo surface.
+  mMaxTextureSize =
+      std::min(Factory::GetMaxSurfaceSize(gfxVars::ContentBackend()),
+               Factory::GetMaxSurfaceSize(BackendType::CAIRO));
+
 }
 
 BasicCompositor::~BasicCompositor() { MOZ_COUNT_DTOR(BasicCompositor); }

widget/gtk/nsWindow.cpp

@@ -117,6 +117,7 @@ using namespace mozilla::widget;
 #include "mozilla/gfx/GPUProcessManager.h"
 #include "mozilla/layers/CompositorBridgeParent.h"
 #include "mozilla/layers/CompositorThread.h"
+#include "mozilla/layers/KnowsCompositor.h"
 
 #ifdef MOZ_X11
 #  include "GLContextGLX.h"  // for GLContextGLX::FindVisual()
@@ -4236,13 +4237,18 @@ LayoutDeviceIntSize nsWindow::GetSafeWindowSize(LayoutDeviceIntSize aSize) {
   // reads it as CARD16.  Sizes of pixmaps, used for drawing, are (unsigned)
   // CARD16 in the protocol, but the server's ProcCreatePixmap returns
   // BadAlloc if dimensions cannot be represented by signed shorts.
+  // Because we are creating Cairo surfaces to represent window buffers,
+  // we also must ensure that the window can fit in a Cairo surface.
   LayoutDeviceIntSize result = aSize;
-  const int32_t kInt16Max = 32767;
-  if (result.width > kInt16Max) {
-    result.width = kInt16Max;
+  int32_t maxSize = 32767;
+  if (mLayerManager && mLayerManager->AsKnowsCompositor()) {
+    maxSize = std::min(maxSize, mLayerManager->AsKnowsCompositor()->GetMaxTextureSize());
   }
-  if (result.height > kInt16Max) {
-    result.height = kInt16Max;
+  if (result.width > maxSize) {
+    result.width = maxSize;
+  }
+  if (result.height > maxSize) {
+    result.height = maxSize;
   }
   return result;
 }