Bug 1802625 - Hide GPU path stroking behind a pref. r=jrmuizel

It seems like this is slow for now until we implement a better way than WPF-gpu-raster
for stroking paths. Just hide this behind a pref so we can at least test it but not
impact performance as badly.

Differential Revision: https://phabricator.services.mozilla.com/D163248

dom/canvas/DrawTargetWebgl.cpp

@@ -2534,8 +2534,11 @@ void PathCache::ClearVertexRanges() {
   }
 }
 
-inline bool DrawTargetWebgl::ShouldAccelPath(const DrawOptions& aOptions) {
-  return mWebglValid && SupportsDrawOptions(aOptions) && PrepareContext();
+inline bool DrawTargetWebgl::ShouldAccelPath(
+    const DrawOptions& aOptions, const StrokeOptions* aStrokeOptions) {
+  return mWebglValid && SupportsDrawOptions(aOptions) &&
+         (!aStrokeOptions || mSharedContext->mPathAccelStroke) &&
+         PrepareContext();
 }
 
 bool DrawTargetWebgl::SharedContext::DrawPathAccel(
@@ -2795,7 +2798,7 @@ void DrawTargetWebgl::DrawPath(const Path* aPath, const Pattern& aPattern,
                                const StrokeOptions* aStrokeOptions) {
   // If there is a WebGL context, then try to cache the path to avoid slow
   // fallbacks.
-  if (ShouldAccelPath(aOptions) &&
+  if (ShouldAccelPath(aOptions, aStrokeOptions) &&
       mSharedContext->DrawPathAccel(aPath, aPattern, aOptions,
                                     aStrokeOptions)) {
     return;
@@ -2890,7 +2893,7 @@ void DrawTargetWebgl::DrawShadow(const Path* aPath, const Pattern& aPattern,
                                  const StrokeOptions* aStrokeOptions) {
   // If there is a WebGL context, then try to cache the path to avoid slow
   // fallbacks.
-  if (ShouldAccelPath(aOptions) &&
+  if (ShouldAccelPath(aOptions, aStrokeOptions) &&
       mSharedContext->DrawPathAccel(aPath, aPattern, aOptions, aStrokeOptions,
                                     &aShadow)) {
     return;
@@ -2907,7 +2910,7 @@ void DrawTargetWebgl::DrawSurfaceWithShadow(SourceSurface* aSurface,
                                             const ShadowOptions& aShadow,
                                             CompositionOp aOperator) {
   DrawOptions options(1.0f, aOperator);
-  if (ShouldAccelPath(options)) {
+  if (ShouldAccelPath(options, nullptr)) {
     SurfacePattern pattern(aSurface, ExtendMode::CLAMP,
                            Matrix::Translation(aDest));
     SkPath skiaPath;
@@ -3733,6 +3736,8 @@ void DrawTargetWebgl::SharedContext::CachePrefs() {
 
   mPathMaxComplexity =
       StaticPrefs::gfx_canvas_accelerated_gpu_path_complexity();
+
+  mPathAccelStroke = StaticPrefs::gfx_canvas_accelerated_gpu_path_stroke();
 }
 
 // For use within CanvasRenderingContext2D, called on BorrowDrawTarget.

dom/canvas/DrawTargetWebgl.h

@@ -176,6 +176,8 @@ class DrawTargetWebgl : public DrawTarget, public SupportsWeakPtr {
     uint32_t mPathVertexCapacity = 0;
     // The maximum supported type complexity of a GPU path.
     uint32_t mPathMaxComplexity = 0;
+    // Whether to accelerate stroked paths.
+    bool mPathAccelStroke = false;
     RefPtr<WebGLProgramJS> mSolidProgram;
     RefPtr<WebGLUniformLocationJS> mSolidProgramViewport;
     RefPtr<WebGLUniformLocationJS> mSolidProgramAA;
@@ -490,7 +492,8 @@ class DrawTargetWebgl : public DrawTarget, public SupportsWeakPtr {
                 bool aAccelOnly = false, bool aForceUpdate = false,
                 const StrokeOptions* aStrokeOptions = nullptr);
 
-  bool ShouldAccelPath(const DrawOptions& aOptions);
+  bool ShouldAccelPath(const DrawOptions& aOptions,
+                       const StrokeOptions* aStrokeOptions);
   void DrawPath(const Path* aPath, const Pattern& aPattern,
                 const DrawOptions& aOptions,
                 const StrokeOptions* aStrokeOptions = nullptr);

modules/libpref/init/StaticPrefList.yaml

@@ -5622,6 +5622,12 @@
   value: 4000
   mirror: always
 
+# Whether to accelerate stroked paths.
+- name: gfx.canvas.accelerated.gpu-path-stroke
+  type: RelaxedAtomicBool
+  value: false
+  mirror: always
+
 # 0x7fff is the maximum supported xlib surface size and is more than enough for canvases.
 - name: gfx.canvas.max-size
   type: RelaxedAtomicInt32