Generic PDF shader fallback

Instead of ignoring unsupported shaders (and essentially filling with
solid black), convert them to bitmap shaders using on-the-fly
rasterization.

BUG=skia:3299
R=reed@google.com,halcanary@google.com

Review URL: https://codereview.chromium.org/841763005

3 files changed, 48 insertions, 15 deletions

diff --git a/src/pdf/SkPDFDevice.cpp b/src/pdf/SkPDFDevice.cpp
index e9a38a0e9b..c3ee262db3 100644
--- a/src/pdf/SkPDFDevice.cpp
+++ b/src/pdf/SkPDFDevice.cpp
@@ -1950,7 +1950,8 @@ void SkPDFDevice::populateGraphicStateEntryFromPaint(
         fInitialTransform.mapRect(&boundsTemp);
         boundsTemp.roundOut(&bounds);
 
-        pdfShader.reset(SkPDFShader::GetPDFShader(*shader, transform, bounds));
+        pdfShader.reset(SkPDFShader::GetPDFShader(*shader, transform, bounds,
+                        SkIntToScalar(fRasterDpi) / DPI_FOR_RASTER_SCALE_ONE));
 
         if (pdfShader.get()) {
             // pdfShader has been canonicalized so we can directly compare
diff --git a/src/pdf/SkPDFShader.cpp b/src/pdf/SkPDFShader.cpp
index 40f7d93f89..890bf447d5 100644
--- a/src/pdf/SkPDFShader.cpp
+++ b/src/pdf/SkPDFShader.cpp
@@ -489,7 +489,7 @@ public:
     SkShader::TileMode fImageTileModes[2];
 
     State(const SkShader& shader, const SkMatrix& canvasTransform,
-          const SkIRect& bbox);
+          const SkIRect& bbox, SkScalar rasterScale);
 
     bool operator==(const State& b) const;
 
@@ -657,10 +657,11 @@ void SkPDFShader::RemoveShader(SkPDFObject* shader) {
 // static
 SkPDFObject* SkPDFShader::GetPDFShader(const SkShader& shader,
                                        const SkMatrix& matrix,
-                                       const SkIRect& surfaceBBox) {
+                                       const SkIRect& surfaceBBox,
+                                       SkScalar rasterScale) {
     SkAutoMutexAcquire lock(CanonicalShadersMutex());
     return GetPDFShaderByState(
-            SkNEW_ARGS(State, (shader, matrix, surfaceBBox)));
+            SkNEW_ARGS(State, (shader, matrix, surfaceBBox, rasterScale)));
 }
 
 // static
@@ -1239,8 +1240,8 @@ bool SkPDFShader::State::operator==(const SkPDFShader::State& b) const {
     return true;
 }
 
-SkPDFShader::State::State(const SkShader& shader,
-                          const SkMatrix& canvasTransform, const SkIRect& bbox)
+SkPDFShader::State::State(const SkShader& shader, const SkMatrix& canvasTransform,
+                          const SkIRect& bbox, SkScalar rasterScale)
         : fCanvasTransform(canvasTransform),
           fBBox(bbox),
           fPixelGeneration(0) {
@@ -1257,10 +1258,39 @@ SkPDFShader::State::State(const SkShader& shader,
         SkMatrix matrix;
         bitmapType = shader.asABitmap(&fImage, &matrix, fImageTileModes);
         if (bitmapType != SkShader::kDefault_BitmapType) {
-            fImage.reset();
-            return;
+            // Generic fallback for unsupported shaders:
+            //  * allocate a bbox-sized bitmap
+            //  * shade the whole area
+            //  * use the result as a bitmap shader
+
+            // Clamp the bitmap size to about 1M pixels
+            static const SkScalar kMaxBitmapArea = 1024 * 1024;
+            SkScalar bitmapArea = rasterScale * bbox.width() * rasterScale * bbox.height();
+            if (bitmapArea > kMaxBitmapArea) {
+                rasterScale *= SkScalarSqrt(SkScalarDiv(kMaxBitmapArea, bitmapArea));
+            }
+
+            SkISize size = SkISize::Make(SkScalarRoundToInt(rasterScale * bbox.width()),
+                                         SkScalarRoundToInt(rasterScale * bbox.height()));
+            SkSize scale = SkSize::Make(SkIntToScalar(size.width()) / SkIntToScalar(bbox.width()),
+                                        SkIntToScalar(size.height()) / SkIntToScalar(bbox.height()));
+
+            fImage.allocN32Pixels(size.width(), size.height());
+            fImage.eraseColor(SK_ColorTRANSPARENT);
+
+            SkPaint p;
+            p.setShader(const_cast<SkShader*>(&shader));
+
+            SkCanvas canvas(fImage);
+            canvas.scale(scale.width(), scale.height());
+            canvas.translate(-SkIntToScalar(bbox.x()), -SkIntToScalar(bbox.y()));
+            canvas.drawPaint(p);
+
+            fShaderTransform.setTranslate(SkIntToScalar(bbox.x()), SkIntToScalar(bbox.y()));
+            fShaderTransform.preScale(1 / scale.width(), 1 / scale.height());
+        } else {
+            SkASSERT(matrix.isIdentity());
         }
-        SkASSERT(matrix.isIdentity());
         fPixelGeneration = fImage.getGenerationID();
     } else {
         AllocateGradientInfoStorage();
diff --git a/src/pdf/SkPDFShader.h b/src/pdf/SkPDFShader.h
index 0b292e932a..9c92d77d92 100644
--- a/src/pdf/SkPDFShader.h
+++ b/src/pdf/SkPDFShader.h
@@ -33,15 +33,17 @@ public:
      *  unreference it when done.  This is needed to accommodate the weak
      *  reference pattern used when the returned object is new and has no
      *  other references.
-     *  @param shader     The SkShader to emulate.
-     *  @param matrix     The current transform. (PDF shaders are absolutely
-     *                    positioned, relative to where the page is drawn.)
-     *  @param surfceBBox The bounding box of the drawing surface (with matrix
-     *                    already applied).
+     *  @param shader      The SkShader to emulate.
+     *  @param matrix      The current transform. (PDF shaders are absolutely
+     *                     positioned, relative to where the page is drawn.)
+     *  @param surfceBBox  The bounding box of the drawing surface (with matrix
+     *                     already applied).
+     *  @param rasterScale Additional scale to be applied for early rasterization.
      */
     static SkPDFObject* GetPDFShader(const SkShader& shader,
                                      const SkMatrix& matrix,
-                                     const SkIRect& surfaceBBox);
+                                     const SkIRect& surfaceBBox,
+                                     SkScalar rasterScale);
 
 protected:
     class State;