Применение Windows API - [30]

 }
 void Step() { ++_tick; }
 void Update(Canvas& canvas);
 void Paint(Canvas& canvas);
private:
 int _cx, _cy;
 int _tick;
 Bitmap _bitmapBuf; // for double buffering
 Bitmap _background;
 int _widthBkg, _heightBkg;
 Bitmap _sprite;
 Bitmap _mask;
 int _widthSprite, _heightSprite;
};

View::View(HINSTANCE hInst) : _tick (0) {
 // Load bitmap from file
 _background.Load("picture.bmp");
 // Load bitmap from resource
 _background.GetSize(_widthBkg, _heightBkg);
 // Load bitmaps from resources
 _sprite.Load(hInst, IDB_FANNY);
 _mask.Load(hInst, IDB_MASK);
 _sprite.GetSize(_widthSprite, _heightSprite);
 DesktopCanvas canvas;
 _bitmapBuf.CreateCompatible(canvas, 1, 1);
 _cx = 1;
 _cy = 1;
}

And here's the implementation of Update. We create a bitmap canvas in memory, making it compatible with the current display canvas. We blit the background image into it, then blit the mask and the sprite (notice the change of position for each frame). Finally, we transfer the complete bitmap into our buffer (overloaded assignment operator at work!).

void View::Update(Canvas& canvas) {
 const double speed = 0.01;
 Bitmap bmp(canvas, _cx, _cy);
 BitmapCanvas bmpCanvas(canvas, bmp);
 RECT rect = { 0, 0, _cx, _cy };
 bmpCanvas.WhiteWash(rect);
 // Do the off-line drawing
 Blitter bltBkg(_background);
 bltBkg.BlitTo(bmpCanvas);
 int xRange = (_widthBkg - _widthSprite) / 2;
 int yRange = (_heightBkg - _heightSprite) / 2;
 int x = xRange + static_cast(xRange * sin(speed * _tick));
 int y = yRange + static_cast(yRange * cos(4 * speed * _tick));
 Blitter bltMask(_mask);
 bltMask.SetMode(SRCPAINT);
 bltMask.SetDest(x, y);
 bltMask.BlitTo(bmpCanvas);
 Blitter bltSprite(_sprite);
 bltSprite.SetMode(SRCAND);
 bltSprite.SetDest(x, y);
 bltSprite.BlitTo(bmpCanvas);
 // update the buffer
 _bitmapBuf = bmp;
}

For completeness, here's the definition of bitmap canvas. You draw directly on this canvas using standard canvas methods, like Line, Text, SetPixel, etc... Here we only blit bitmaps into it.

class BitmapCanvas: public MemCanvas {
public:
 BitmapCanvas(HDC hdc, HBITMAP hBitmap) : MemCanvas(hdc) {
  // convert bitmap to format compatible with canvas
  _hOldBitmap = reinterpret_cast(::SelectObject(_hdc, hBitmap));
 }
 ~BitmapCanvas() {
  ::SelectObject(_hdc, _hOldBitmap);
 }
private:
 HBITMAP _hOldBitmap;
};

class MemCanvas: public Canvas {
public:
 MemCanvas(HDC hdc) : Canvas(::CreateCompatibleDC(hdc)) {}
 ~MemCanvas() {
  ::DeleteDC(_hdc);
 }
};

Now, if you want more speed, read about DirectDraw.