Keep the cairo clipping region in sync with the Skia one.

skia/ext/bitmap_platform_device_linux.cc

Index: skia/ext/bitmap_platform_device_linux.cc
diff --git a/skia/ext/bitmap_platform_device_linux.cc b/skia/ext/bitmap_platform_device_linux.cc
index 1b061b00d823288edaf7db25fe72a264c799731e..a74ec830561efed9f7b90c89951af485817683d8 100644
--- a/skia/ext/bitmap_platform_device_linux.cc
+++ b/skia/ext/bitmap_platform_device_linux.cc
@@ -1,4 +1,4 @@
-// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
+// 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.
 
@@ -8,6 +8,33 @@
 
 namespace skia {
 
+namespace {
+
+void LoadMatrixToContext(cairo_t* context, const SkMatrix& matrix) {
+  cairo_matrix_t cairo_matrix;
+  cairo_matrix_init(&cairo_matrix,
+                    SkScalarToFloat(matrix.getScaleX()),
+                    SkScalarToFloat(matrix.getSkewY()),
+                    SkScalarToFloat(matrix.getSkewX()),
+                    SkScalarToFloat(matrix.getScaleY()),
+                    SkScalarToFloat(matrix.getTranslateX()),
+                    SkScalarToFloat(matrix.getTranslateY()));
+  cairo_set_matrix(context, &cairo_matrix);
+}
+
+void LoadClipToContext(cairo_t* context, const SkRegion& clip) {
+  cairo_reset_clip(context);
+
+  // TODO(brettw) support non-rect clips.
+  SkIRect bounding = clip.getBounds();
+  cairo_rectangle(context, bounding.fLeft, bounding.fTop,
+                  bounding.fRight - bounding.fLeft,
+                  bounding.fBottom - bounding.fTop);
+  cairo_clip(context);
+}
+
+}  // namespace
+
 // -----------------------------------------------------------------------------
 // These objects are reference counted and own a Cairo surface. The surface is
 // the backing store for a Skia bitmap and we reference count it so that we can
@@ -17,18 +44,39 @@ namespace skia {
 class BitmapPlatformDevice::BitmapPlatformDeviceData
     : public base::RefCounted<BitmapPlatformDeviceData> {
  public:
-  explicit BitmapPlatformDeviceData(cairo_surface_t* surface)
-      : surface_(surface) { }
+  explicit BitmapPlatformDeviceData(cairo_surface_t* surface);
 
-  cairo_surface_t* surface() const { return surface_; }
+  cairo_t* GetContext();
+  cairo_surface_t* GetSurface();
+
+  // Sets the transform and clip operations. This will not update the Cairo
+  // surface, but will mark the config as dirty. The next call of LoadConfig
+  // will pick up these changes.
+  void SetMatrixClip(const SkMatrix& transform, const SkRegion& region);
 
  protected:
+  friend class base::RefCounted<BitmapPlatformDeviceData>;
+
+  ~BitmapPlatformDeviceData();
+
+  void LoadConfig();
+
+  // The Cairo surface inside this DC.
+  cairo_t* context_;
   cairo_surface_t *const surface_;
 
-  friend class base::RefCounted<BitmapPlatformDeviceData>;
-  ~BitmapPlatformDeviceData() {
-    cairo_surface_destroy(surface_);
-  }
+  // True when there is a transform or clip that has not been set to the
+  // surface.  The surface is retrieved for every text operation, and the
+  // transform and clip do not change as much. We can save time by not loading
+  // the clip and transform for every one.
+  bool config_dirty_;
+
+  // Translation assigned to the DC: we need to keep track of this separately
+  // so it can be updated even if the DC isn't created yet.
+  SkMatrix transform_;
+
+  // The current clipping
+  SkRegion clip_region_;
 
   // Disallow copy & assign.
   BitmapPlatformDeviceData(const BitmapPlatformDeviceData&);
@@ -36,6 +84,52 @@ class BitmapPlatformDevice::BitmapPlatformDeviceData
       const BitmapPlatformDeviceData&);
 };
 
+BitmapPlatformDevice::BitmapPlatformDeviceData::BitmapPlatformDeviceData(
+    cairo_surface_t* surface)
+    : surface_(surface),
+      config_dirty_(true) {  // Want to load the config next time.
+  context_ = cairo_create(surface);
+}
+
+BitmapPlatformDevice::BitmapPlatformDeviceData::~BitmapPlatformDeviceData() {
+  cairo_destroy(context_);
+  cairo_surface_destroy(surface_);
+}
+
+cairo_t* BitmapPlatformDevice::BitmapPlatformDeviceData::GetContext() {
+  LoadConfig();
+  return context_;
+}
+
+void BitmapPlatformDevice::BitmapPlatformDeviceData::SetMatrixClip(
+    const SkMatrix& transform,
+    const SkRegion& region) {
+  transform_ = transform;
+  clip_region_ = region;
+  config_dirty_ = true;
+}
+
+cairo_surface_t*
+BitmapPlatformDevice::BitmapPlatformDeviceData::GetSurface() {
+  // TODO(brettw) this function should be removed.
+  LoadConfig();
+  return surface_;
+}
+
+void BitmapPlatformDevice::BitmapPlatformDeviceData::LoadConfig() {
+  if (!config_dirty_ || !context_)
+    return;  // Nothing to do.
+  config_dirty_ = false;
+
+  // Load the identity matrix since this is what our clip is relative to.
+  cairo_matrix_t cairo_matrix;
+  cairo_matrix_init_identity(&cairo_matrix);
+  cairo_set_matrix(context_, &cairo_matrix);
+
+  LoadClipToContext(context_, clip_region_);
+  LoadMatrixToContext(context_, transform_);
+}
+
 // We use this static factory function instead of the regular constructor so
 // that we can create the pixel data before calling the constructor. This is
 // required so that we can call the base class' constructor with the pixel
@@ -98,8 +192,13 @@ BitmapPlatformDevice::BitmapPlatformDevice(
 BitmapPlatformDevice::~BitmapPlatformDevice() {
 }
 
-cairo_surface_t* BitmapPlatformDevice::surface() const {
-  return data_->surface();
+cairo_t* BitmapPlatformDevice::beginPlatformPaint() {
+  return data_->GetContext();
+}
+
+void BitmapPlatformDevice::setMatrixClip(const SkMatrix& transform,
+                                         const SkRegion& region) {
+  data_->SetMatrixClip(transform, region);
 }
 
 BitmapPlatformDevice& BitmapPlatformDevice::operator=(