Refactor the PlatformContext layer to have only one class.

skia/ext/canvas_paint_win.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_WIN_H_
+#define SKIA_EXT_CANVAS_PAINT_WIN_H_
+
+#include "skia/ext/platform_canvas.h"
+
+namespace skia {
+
+// A class designed to help with WM_PAINT operations on Windows. It will
+// do BeginPaint/EndPaint on init/destruction, and will create the bitmap and
+// canvas with the correct size and transform for the dirty rect. The bitmap
+// will be automatically painted to the screen on destruction.
+//
+// You MUST call isEmpty before painting to determine if anything needs
+// painting. Sometimes the dirty rect can actually be empty, and this makes
+// the bitmap functions we call unhappy. The caller should not paint in this
+// case.
+//
+// Therefore, all you need to do is:
+//   case WM_PAINT: {
+//     gfx::PlatformCanvasPaint canvas(hwnd);
+//     if (!canvas.isEmpty()) {
+//       ... paint to the canvas ...
+//     }
+//     return 0;
+//   }
+template <class T>
+class CanvasPaintT : public T {
+ public:
+  // This constructor assumes the canvas is opaque.
+  explicit CanvasPaintT(HWND hwnd) : hwnd_(hwnd), paint_dc_(NULL),
+    for_paint_(true) {
+    memset(&ps_, 0, sizeof(ps_));
+    initPaint(true);
+  }
+
+  CanvasPaintT(HWND hwnd, bool opaque) : hwnd_(hwnd), paint_dc_(NULL),
+      for_paint_(true) {
+    memset(&ps_, 0, sizeof(ps_));
+    initPaint(opaque);
+  }
+
+  // Creates a CanvasPaintT for the specified region that paints to the
+  // specified dc. This does NOT do BeginPaint/EndPaint.
+  CanvasPaintT(HDC dc, bool opaque, int x, int y, int w, int h)
+      : hwnd_(NULL),
+        paint_dc_(dc),
+        for_paint_(false) {
+    memset(&ps_, 0, sizeof(ps_));
+    ps_.rcPaint.left = x;
+    ps_.rcPaint.right = x + w;
+    ps_.rcPaint.top = y;
+    ps_.rcPaint.bottom = y + h;
+    init(opaque);
+  }
+
+  virtual ~CanvasPaintT() {
+    if (!isEmpty()) {
+      restoreToCount(1);
+      // Commit the drawing to the screen
+      getTopPlatformDevice().drawToHDC(paint_dc_,
+                                       ps_.rcPaint.left, ps_.rcPaint.top,
+                                       NULL);
+    }
+    if (for_paint_)
+      EndPaint(hwnd_, &ps_);
+  }
+
+  // Returns true if the invalid region is empty. The caller should call this
+  // function to determine if anything needs painting.
+  bool isEmpty() const {
+    return ps_.rcPaint.right - ps_.rcPaint.left == 0 ||
+           ps_.rcPaint.bottom - ps_.rcPaint.top == 0;
+  }
+
+  // Use to access the Windows painting parameters, especially useful for
+  // getting the bounding rect for painting: paintstruct().rcPaint
+  const PAINTSTRUCT& paintStruct() const {
+    return ps_;
+  }
+
+  // Returns the DC that will be painted to
+  HDC paintDC() const {
+    return paint_dc_;
+  }
+
+ protected:
+  HWND hwnd_;
+  HDC paint_dc_;
+  PAINTSTRUCT ps_;
+
+ private:
+  void initPaint(bool opaque) {
+    paint_dc_ = BeginPaint(hwnd_, &ps_);
+
+    init(opaque);
+  }
+
+  void init(bool opaque) {
+    // FIXME(brettw) for ClearType, we probably want to expand the bounds of
+    // painting by one pixel so that the boundaries will be correct (ClearType
+    // text can depend on the adjacent pixel). Then we would paint just the
+    // inset pixels to the screen.
+    const int width = ps_.rcPaint.right - ps_.rcPaint.left;
+    const int height = ps_.rcPaint.bottom - ps_.rcPaint.top;
+    if (!initialize(width, height, opaque, NULL)) {
+      // Cause a deliberate crash;
+      *(char*) 0 = 0;
+    }
+
+    // This will bring the canvas into the screen coordinate system for the
+    // dirty rect
+    translate(SkIntToScalar(-ps_.rcPaint.left),
+              SkIntToScalar(-ps_.rcPaint.top));
+  }
+
+  // If true, this canvas was created for a BeginPaint.
+  const bool for_paint_;
+
+  // Disallow copy and assign.
+  CanvasPaintT(const CanvasPaintT&);
+  CanvasPaintT& operator=(const CanvasPaintT&);
+};
+
+typedef CanvasPaintT<PlatformCanvas> PlatformCanvasPaint;
+
+}  // namespace skia
+
+#endif  // SKIA_EXT_CANVAS_PAINT_WIN_H_