Bug 1843891 - Enable to present WebGPU without readback with DX12 on Windows r=webgpu-reviewers,nical

Differential Revision: https://phabricator.services.mozilla.com/D190250

dom/webgpu/CanvasContext.cpp

@@ -126,6 +126,9 @@ void CanvasContext::Configure(const dom::GPUCanvasConfiguration& aConfig) {
   mUseExternalTextureInSwapChain =
       wgpu_client_use_external_texture_in_swapChain(
           aConfig.mDevice->mId, ConvertTextureFormat(aConfig.mFormat));
+  if (!gfx::gfxVars::AllowWebGPUPresentWithoutReadback()) {
+    mUseExternalTextureInSwapChain = false;
+  }
 #ifdef XP_WIN
   // When WebRender does not use hardware acceleration, disable external texture
   // in swap chain. Since compositor device might not exist.

gfx/config/gfxVars.h

@@ -101,7 +101,8 @@ class gfxVarReceiver;
   _(AllowSoftwareWebRenderOGL, bool, false)                        \
   _(WebglUseHardware, bool, true)                                  \
   _(WebRenderOverlayVpAutoHDR, bool, false)                        \
-  _(WebRenderOverlayVpSuperResolution, bool, false)
+  _(WebRenderOverlayVpSuperResolution, bool, false)                \
+  _(AllowWebGPUPresentWithoutReadback, bool, false)
 
 /* Add new entries above this line. */
 

gfx/thebes/gfxPlatform.cpp

@@ -3162,6 +3162,13 @@ void gfxPlatform::InitWebGPUConfig() {
 #endif
 
   gfxVars::SetAllowWebGPU(feature.IsEnabled());
+
+#if XP_WIN
+  if (IsWin10CreatorsUpdateOrLater() &&
+      StaticPrefs::dom_webgpu_allow_present_without_readback()) {
+    gfxVars::SetAllowWebGPUPresentWithoutReadback(true);
+  }
+#endif
 }
 
 #ifdef XP_WIN

gfx/wgpu_bindings/src/client.rs

@@ -1346,10 +1346,6 @@ pub extern "C" fn wgpu_client_use_external_texture_in_swapChain(
         return false;
     }
 
-    if !static_prefs::pref!("dom.webgpu.swap-chain.external-texture-dx12") {
-        return false;
-    }
-
     let supported = match format {
         wgt::TextureFormat::Bgra8Unorm => true,
         _ => false,

modules/libpref/init/StaticPrefList.yaml

@@ -4637,11 +4637,14 @@
   mirror: always
   rust: true
 
-- name: dom.webgpu.swap-chain.external-texture-dx12
+- name: dom.webgpu.allow-present-without-readback
   type: RelaxedAtomicBool
+#if defined(XP_WIN)
+  value: true
+#else
   value: false
+#endif
   mirror: always
-  rust: true
 
 # For testing purposes, crash if we don't get a hardware adapter.
 - name: dom.webgpu.testing.assert-hardware-adapter