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// Copyright (c) 2011 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.
#pragma once
#include "skia/ext/canvas_paint_common.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;
// }
// Note: The created context is always inialized to (0, 0, 0, 0).
template <class T>
class CanvasPaintT : public T {
// This constructor assumes the canvas is opaque.
explicit CanvasPaintT(HWND hwnd) : hwnd_(hwnd), paint_dc_(NULL),
for_paint_(true) {
memset(&ps_, 0, sizeof(ps_));
CanvasPaintT(HWND hwnd, bool opaque) : hwnd_(hwnd), paint_dc_(NULL),
for_paint_(true) {
memset(&ps_, 0, sizeof(ps_));
// 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),
for_paint_(false) {
memset(&ps_, 0, sizeof(ps_));
ps_.rcPaint.left = x;
ps_.rcPaint.right = x + w; = y;
ps_.rcPaint.bottom = y + h;
virtual ~CanvasPaintT() {
if (!isEmpty()) {
PlatformCanvas* canvas = GetPlatformCanvas(this);
// Commit the drawing to the screen
skia::DrawToNativeContext(canvas, paint_dc_, ps_.rcPaint.left,, 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 - == 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_;
HWND hwnd_;
HDC paint_dc_;
void initPaint(bool opaque) {
paint_dc_ = BeginPaint(hwnd_, &ps_);
void init(bool opaque) {
PlatformCanvas* canvas = GetPlatformCanvas(this);
// 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 -;
if (!canvas->initialize(width, height, opaque, NULL)) {
// Cause a deliberate crash;
*(char*) 0 = 0;
canvas->clear(SkColorSetARGB(0, 0, 0, 0));
// This will bring the canvas into the screen coordinate system for the
// dirty rect
// 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
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