A canvas_paint for OS X.

skia/ext/canvas_paint_mac.h

+
+// Copyright (c) 2009 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef SKIA_EXT_CANVAS_PAINT_MAC_H_
+#define SKIA_EXT_CANVAS_PAINT_MAC_H_
+
+#include "skia/ext/platform_canvas.h"
+
+#import <Cocoa/Cocoa.h>
+
+namespace skia {
+
+// A class designed to translate skia painting into a region to the current
+// graphics context. This class has been adapted from the class with the same
+// name in platform_canvas_win.h. On construction, it will set up a context for
+// painting into, and on destruction, it will commit it to the current context.
+template <class T>
+class CanvasPaintT : public T {
+ public:
+  // This constructor assumes the result is opaque.
+  explicit CanvasPaintT(NSRect dirtyRect)
+      : context_(NULL),
+        rectangle_(dirtyRect),
+        composite_alpha_(false) {
+    init(true);
+  }
+
+  CanvasPaintT(NSRect dirtyRect, bool opaque)
+      : context_(NULL),
+        rectangle_(dirtyRect),
+        composite_alpha_(false) {
+    init(opaque);
+  }
+
+  virtual ~CanvasPaintT() {
+    if (!is_empty()) {
+      T::restoreToCount(1);
+
+      // Blit the dirty rect to the current context.
+      CGImageRef image = CGBitmapContextCreateImage(context_);
+      CGRect destRect = NSRectToCGRect(rectangle_);
+
+      CGContextRef context =
+          (CGContextRef)[[NSGraphicsContext currentContext] graphicsPort];
+      CGContextSaveGState(context);
+      CGContextSetBlendMode(
+          context, composite_alpha_ ? kCGBlendModeNormal : kCGBlendModeCopy);
+      CGContextDrawImage(context, destRect, image);
+      CGContextRestoreGState(context);
+
+      CFRelease(image);
+    }
+  }
+
+  // If true, the data painted into the CanvasPaintT is blended onto the current
+  // context, else it is copied.
+  void set_composite_alpha(bool composite_alpha) {
+    composite_alpha_ = composite_alpha;
+  }
+
+  // Returns true if the invalid region is empty. The caller should call this
+  // function to determine if anything needs painting.
+  bool is_empty() const {
+    return rectangle_.size.width == 0 || rectangle_.size.height == 0;
+  }
+
+  const NSRect& rectangle() const {
+    return rectangle_;
+  }
+
+ private:
+  void init(bool opaque) {
+    if (!T::initialize(rectangle_.size.width, rectangle_.size.height,
+                       opaque, NULL)) {
+      // Cause a deliberate crash;
+      *(char*) 0 = 0;
+    }
+
+    // Need to translate so that the dirty region appears at the origin of the
+    // surface.
+    T::translate(-SkIntToScalar(rectangle_.origin.x),
+                 -SkIntToScalar(rectangle_.origin.y));
+
+    context_ = T::getTopPlatformDevice().GetBitmapContext();
+  }
+
+  CGContext* context_;
+  NSRect rectangle_;
+  // See description above setter.
+  bool composite_alpha_;
+
+  // Disallow copy and assign.
+  CanvasPaintT(const CanvasPaintT&);
+  CanvasPaintT& operator=(const CanvasPaintT&);
+};
+
+typedef CanvasPaintT<PlatformCanvas> PlatformCanvasPaint;
+
+}  // namespace skia
+
+
+#endif  // SKIA_EXT_CANVAS_PAINT_MAC_H_