[canvaskit] Fallback to CPU more gracefully

This should also trim down code size since WebGL should never want
GrGLMakeAssembledGLInterface only GrGLMakeAssembledGLESInterface

Bug: skia:
Change-Id: I9246d467847eeb91517c56075077b3e26c4ee336
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/201223
Reviewed-by: Nathaniel Nifong <nifong@google.com>

modules/canvaskit/CHANGELOG.md

@@ -11,6 +11,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
  - Extern bug in `CanvasKit.SkMatrix.invert`
+ - Fallback to CPU now properly refreshes the canvas to get access to the
+   CanvasRenderingContext2D.
 
 ## [0.5.0] - 2019-03-08
 

modules/canvaskit/compile.sh

@@ -249,5 +249,6 @@ ${EMCXX} \
     -s USE_FREETYPE=1 \
     -s USE_LIBPNG=1 \
     -s WARN_UNALIGNED=1 \
+    -s USE_WEBGL2=0 \
     -s WASM=1 \
     -o $BUILD_DIR/canvaskit.js

modules/canvaskit/gpu.js

@@ -79,7 +79,15 @@
                                                  height || canvas.height);
         if (!surface) {
           SkDebug('falling back from GPU implementation to a SW based one');
-          return CanvasKit.MakeSWCanvasSurface(arg);
+          // we need to throw away the old canvas (which was locked to
+          // a webGL context) and create a new one so we can
+          var newCanvas = canvas.cloneNode(true);
+          var parent = canvas.parentNode;
+          parent.replaceChild(newCanvas, canvas);
+          // add a class so the user can detect that it was replaced.
+          newCanvas.classList.add('ck-replaced');
+
+          return CanvasKit.MakeSWCanvasSurface(newCanvas);
         }
         return surface;
       };

src/gpu/gl/GrGLAssembleInterface.cpp

@@ -16,6 +16,9 @@
 #define GET_EGL_PROC_SUFFIX(F, S) functions->fEGL##F = (GrEGL##F##Fn*)get(ctx, "egl" #F #S)
 
 sk_sp<const GrGLInterface> GrGLMakeAssembledInterface(void *ctx, GrGLGetProc get) {
+#if IS_WEBGL==1
+    return GrGLMakeAssembledGLESInterface(ctx, get);
+#else
     GET_PROC_LOCAL(GetString);
     if (nullptr == GetString) {
         return nullptr;
@@ -34,6 +37,7 @@ sk_sp<const GrGLInterface> GrGLMakeAssembledInterface(void *ctx, GrGLGetProc get
         return GrGLMakeAssembledGLInterface(ctx, get);
     }
     return nullptr;
+#endif
 }
 
 static void get_egl_query_and_display(GrEGLQueryStringFn** queryString, GrEGLDisplay* display,

src/gpu/gl/GrGLCaps.cpp

@@ -19,7 +19,7 @@
 #include "SkTSearch.h"
 #include "SkTSort.h"
 
-#if IS_WEBGL
+#if IS_WEBGL==1
 static constexpr bool kIsWebGL = true;
 #else
 static constexpr bool kIsWebGL = false;