Goal: ensure we always balance lock/unlock pixels calls.

A big caller of lockPixels is setContext in the bitmapshader.

This change replaces beginSession/endSession with adding endContext(), and
adds debugging code to ensure that
1. setContext calls are never nested
2. endContext is always called after each setContext call.
Review URL: https://codereview.appspot.com/6937046

git-svn-id: http://skia.googlecode.com/svn/trunk@6798 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 31 insertions, 21 deletions

diff --git a/src/core/SkBlitter.cpp b/src/core/SkBlitter.cpp
index 85331c23c3..1234f43c3f 100644
--- a/src/core/SkBlitter.cpp
+++ b/src/core/SkBlitter.cpp
@@ -572,16 +572,30 @@ public:
     void setMask(const SkMask* mask) { fMask = mask; }
 
     virtual bool setContext(const SkBitmap& device, const SkPaint& paint,
-                            const SkMatrix& matrix) {
+                            const SkMatrix& matrix) SK_OVERRIDE {
+        if (!this->INHERITED::setContext(device, paint, matrix)) {
+            return false;
+        }
         if (fProxy) {
-            return fProxy->setContext(device, paint, matrix);
+            if (!fProxy->setContext(device, paint, matrix)) {
+                // must keep our set/end context calls balanced
+                this->INHERITED::endContext();
+                return false;
+            }
         } else {
             fPMColor = SkPreMultiplyColor(paint.getColor());
-            return this->INHERITED::setContext(device, paint, matrix);
         }
+        return true;
+    }
+    
+    virtual void endContext() SK_OVERRIDE {
+        if (fProxy) {
+            fProxy->endContext();
+        }
+        this->INHERITED::endContext();
     }
 
-    virtual void shadeSpan(int x, int y, SkPMColor span[], int count) {
+    virtual void shadeSpan(int x, int y, SkPMColor span[], int count) SK_OVERRIDE {
         if (fProxy) {
             fProxy->shadeSpan(x, y, span, count);
         }
@@ -645,20 +659,6 @@ public:
         }
     }
 
-    virtual void beginSession() {
-        this->INHERITED::beginSession();
-        if (fProxy) {
-            fProxy->beginSession();
-        }
-    }
-
-    virtual void endSession() {
-        if (fProxy) {
-            fProxy->endSession();
-        }
-        this->INHERITED::endSession();
-    }
-
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(Sk3DShader)
 
 protected:
@@ -907,8 +907,17 @@ SkBlitter* SkBlitter::Choose(const SkBitmap& device,
         // if there is one, the shader will take care of it.
     }
 
+    /*
+     *  We need to have balanced calls to the shader:
+     *      setContext
+     *      endContext
+     *  We make the first call here, in case it fails we can abort the draw.
+     *  The endContext() call is made by the blitter (assuming setContext did
+     *  not fail) in its destructor.
+     */
     if (shader && !shader->setContext(device, *paint, matrix)) {
-        return SkNEW(SkNullBlitter);
+        SK_PLACEMENT_NEW(blitter, SkNullBlitter, storage, storageSize);
+        return blitter;
     }
 
     switch (device.getConfig()) {
@@ -978,14 +987,15 @@ SkShaderBlitter::SkShaderBlitter(const SkBitmap& device, const SkPaint& paint)
         : INHERITED(device) {
     fShader = paint.getShader();
     SkASSERT(fShader);
+    SkASSERT(fShader->setContextHasBeenCalled());
 
     fShader->ref();
-    fShader->beginSession();
     fShaderFlags = fShader->getFlags();
 }
 
 SkShaderBlitter::~SkShaderBlitter() {
-    fShader->endSession();
+    SkASSERT(fShader->setContextHasBeenCalled());
+    fShader->endContext();
     fShader->unref();
 }