также. И так далее, пока пользователь не отпустит кнопку мыши.
void SplitController::LButtonUp(POINTS pt) {
// Calling ReleaseCapture will send us the WM_CAPTURECHANGED
_hwnd.ReleaseMouse();
_hwndParent.SendMessage(MSG_MOVESPLITTER, _dragStart + pt.x);
}
В этой точке мы должны стереть вертикальную строку в последний раз. Однако, мы не делаем это непосредственно — мы используем здесь небольшой прием. Мы прекращаем сбор данных мыши. Как побочный эффект, Windows посылает нам сообщение WM_CAPTURECHANGED. Во время обработки этого сообщения, мы фактически и стираем вертикальную строку.
void SplitController::CaptureChanged() {
// We are losing capture
// End drag selection -- for whatever reason
// Erase previous divider
UpdateCanvas canvas(_hwndParent);
ModeSetter mode(canvas, R2_NOTXORPEN);
canvas.Line(_dragX, 0, _dragX, _cy - 1);
}
Почему мы делаем это таким образом? Потому, что Windows может заставить нас, прекратить обработку данных от мыши прежде, чем пользователь опустит ее кнопку. Это может случиться, например, когда другое приложение внезапно решает распахнуть его окно, в то время как пользователь находится в процессе перемещения. В этом случае наше окно никогда не получило бы сообщение об отжатии кнопки. Если бы мы не были так умны, мы бы не были способны чисто перемещаться. К счастью, перед завершением обработки данных мыши, Windows сумеет послать нам сообщение WM_CAPTURECHANGED, и мы примем его к сведению, чтобы сделать нашу очистку.
Вернемся снова к LBUTTONUP — когда пользователь заканчивает перемещение, мы посылаем родителю наше специальное сообщение MSG_MOVESPLITTER, передавая ему новую позицию центра полосы расщепителя, измеряемой в координатах клиентской области родителя. Вы уже видели клиентский код, реагирующий на это сообщение.
Здесь показано, как можно определить клиентское сообщение.
// Reserved by Reliable Software Library
const UINT MSG_RS_LIBRARY = WM_USER + 0x4000;
// wParam = new position wrt parent's left edge
const UINT MSG_MOVESPLITTER = MSG_RS_LIBRARY + 1;
В заключение представлен фрагмент из очень полезного класса HWnd, который инкапсулирует многие базисных функции API Windows, имеющие дело с окнами. В частности, рассмотрите методы MoveDelayPaint и ForceRepaint, который мы использовали в перерисовке полоски расщепителя.
class HWnd {
public:
void Update() {
::UpdateWindow(_hwnd);
}
// Moving
void Move(int x, int y, int width, int height) {
::MoveWindow(_hwnd, x, y, width, height, TRUE);
}
void MoveDelayPaint(int x, int y, int width, int height) {
::MoveWindow(_hwnd, x, y, width, height, FALSE);
}
// Repainting
void Invalidate() {
::InvalidateRect(_hwnd, 0, TRUE);
}
void ForceRepaint() {
Invalidate();
Update();
}
private:
HWND _hwnd;
};
Как обычно, Вы можете загрузить полный исходный текст приложения, которое использовалось в этом примере.
Далее: Следующая обучающая программа рассказывает о растрах.
(обратно)
void Bitmap::Load(HINSTANCE hInst, int id) { Free(); _hBitmap = (HBITMAP)::LoadImage(hInst, MAKEINTRESOURCE(id), IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION); if (_hBitmap == 0) throw WinException("Cannot load bitmap from resources"); } Loading a bitmap directly from a file is also very simple and can be done using the same API, LoadImage. Remember, it will only work if the file is a Windows (or OS/2) bitmap — such files usually have the extension .bmp. There is no simple way of loading other types of graphics files, .gif, .jpg, .png, etc. You have to know their binary layout and decode them explicitly (there are other web sites that have this information). void Bitmap::Load(char* path) { Free(); _hBitmap = (HBITMAP)::LoadImage(0, path, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE); if(_hBitmap == 0) throw WinException("Cannot load bitmap from file", path); } Once you got hold of a bitmap, you may want to enquire about its dimensions. Here's how you do it. void Bitmap::GetSize(int& width, int& height) { BITMAP bm; ::GetObject(_hBitmap, sizeof(bm), &bm); width = bm.bmWidth; height = bm.bmHeight; } Finally, you might want to create an empty bitmap and fill it with your own drawings programmatically. You have to specify the dimensions of the bitmap and you have to provide a device context (Canvas) for which the bitmap is targeted. Windows will create a different type of bitmap when your target is a monochrome monitor or printer, and different when it's a graphics card set to True Color. Windows will create a bitmap that is compatible with the target device. Bitmap::Bitmap(Canvas& canvas, int dx, int dy) : _hBitmap (0) { CreateCompatible(canvas, dx, dy); }
void Bitmap::CreateCompatible(Canvas& canvas, int width, int height) { Free(); _hBitmap = ::CreateCompatibleBitmap(canvas, width, height); } How do you display the bitmap on screen? You have to blit it. Blit stands for "block bit transfer" or something like that. When you blit a bitmap, you have to specify a lot of parameters, so we'll just encapsulate the blitting request in a separate object, the blitter. This is a very handy object that sets the obvious defaults for blitting, but at the same time lets you override each and any of them. A blitter transfers a rectangular area of the bitmap into a rectangular area of the screen. The meaning of various parameters is the following: • Source position: pixel coordinates of the upper left corner of the bitmap area, to be transferred. The default is the upper left corner of the bitmap. • Destination position: pixel coordinates within the target window of the upper left corner of the transferred area. The default is upper left corner of the window. • Area dimensions: the dimensions of the rectangular area to be transferred. The default is the dimensions of the bitmap. • Transfer mode. The way bitmap pixels are combined with existing window pixels. The default, SRCCOPY, copies the pixels over existing pixels. You may also specify more involved logical operations, like SRCAND (Boolean AND), SRCPAINT (Boolean OR), etc. (see your compiler's help on BitBlt). class Blitter { public: Blitter(Bitmap& bmp) : _bmp (bmp), _mode (SRCCOPY), _xDst (0), _yDst (0), _xSrc (0), _ySrc (0) { bmp.GetSize(_width, _height); } void SetMode(DWORD mode) { _mode = mode; } void SetDest(int x, int y) { _xDst = x; _yDst = y; } void SetSrc(int x, int y) { _xSrc = x; _ySrc = y; } void SetArea(int width, int height) { _width = width; _height = height; } // transfer bitmap to canvas void BlitTo(Canvas & canvas); private: Bitmap& _bmp; int _xDst, _yDst; int _xSrc, _ySrc; int _width, _height; DWORD _mode; }; The BlitTo method performs
Bitmaps
In this tutorial we'll learn how to load bitmaps from resources and from files, how to pass them around and blit them to the screen. We'll also see how to create and use an empty bitmap as a canvas, draw a picture on it and then blit it to the screen. Finally, we'll combine these techniques to write a simple program that uses double-buffering and timer messages to show a simple animation involving sprites. First of all, in most cases Windows provides storage for bitmaps and takes care of the formatting of bits. The programmer gets access to the bitmap through a handle, whose type is HBITMAP. (Remember to set the STRICT flag when compiling Windows programs, to make sure HBITMAP is a distinct type, rather than just a pointer to void.) Since a bitmap is a resource (in the Resource Management sense), the first step is to encapsulate it in a “strong pointer” type of interface. Notice the transfer semantics of the constructor and the overloaded assignment operator, characteristic of a resource that can have only one owner at a time. We instruct Windows to release the resources allocated to the bitmap by calling DeleteObject. class Bitmap { public: Bitmap() : _hBitmap (0) {} // Transfer semantics Bitmap(Bitmap& bmp) : _hBitmap(bmp.Release()) {} void operator=(Bitmap& bmp) { if (bmp._hBitmap != _hBitmap) { Free(); _hBitmap = bmp.Release(); } } HBITMAP Release() { HBITMAP h = _hBitmap; _hBitmap = 0; return h; } ~Bitmap() { Free(); } // implicit conversion for use with Windows API operator HBITMAP() { return _hBitmap; } protected: Bitmap(HBITMAP hBitmap) : _hBitmap(hBitmap) {} void Free() { if (_hBitmap) ::DeleteObject(_hBitmap); } HBITMAP _hBitmap; }; Now that the management issues are out of the way, we can concentrate on loading bitmaps. The simplest way to include a bitmap in your program is to add it to the resource file. In the resource editor of your development environment you can create new bitmaps or import them from external files. You can either give them names (strings) or numerical ids. When you want to access such a bitmap in your program you have to load it from the resources. Here are two methods that do just that. You have to give them a handle to the program instance. void Bitmap::Load(HINSTANCE hInst, char const * resName) { Free(); _hBitmap = (HBITMAP)::LoadImage(hInst, resName, IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION); if (_hBitmap == 0) throw WinException("Cannot load bitmap from resources", resName); }void Bitmap::Load(HINSTANCE hInst, int id) { Free(); _hBitmap = (HBITMAP)::LoadImage(hInst, MAKEINTRESOURCE(id), IMAGE_BITMAP, 0, 0, LR_CREATEDIBSECTION); if (_hBitmap == 0) throw WinException("Cannot load bitmap from resources"); } Loading a bitmap directly from a file is also very simple and can be done using the same API, LoadImage. Remember, it will only work if the file is a Windows (or OS/2) bitmap — such files usually have the extension .bmp. There is no simple way of loading other types of graphics files, .gif, .jpg, .png, etc. You have to know their binary layout and decode them explicitly (there are other web sites that have this information). void Bitmap::Load(char* path) { Free(); _hBitmap = (HBITMAP)::LoadImage(0, path, IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE); if(_hBitmap == 0) throw WinException("Cannot load bitmap from file", path); } Once you got hold of a bitmap, you may want to enquire about its dimensions. Here's how you do it. void Bitmap::GetSize(int& width, int& height) { BITMAP bm; ::GetObject(_hBitmap, sizeof(bm), &bm); width = bm.bmWidth; height = bm.bmHeight; } Finally, you might want to create an empty bitmap and fill it with your own drawings programmatically. You have to specify the dimensions of the bitmap and you have to provide a device context (Canvas) for which the bitmap is targeted. Windows will create a different type of bitmap when your target is a monochrome monitor or printer, and different when it's a graphics card set to True Color. Windows will create a bitmap that is compatible with the target device. Bitmap::Bitmap(Canvas& canvas, int dx, int dy) : _hBitmap (0) { CreateCompatible(canvas, dx, dy); }
void Bitmap::CreateCompatible(Canvas& canvas, int width, int height) { Free(); _hBitmap = ::CreateCompatibleBitmap(canvas, width, height); } How do you display the bitmap on screen? You have to blit it. Blit stands for "block bit transfer" or something like that. When you blit a bitmap, you have to specify a lot of parameters, so we'll just encapsulate the blitting request in a separate object, the blitter. This is a very handy object that sets the obvious defaults for blitting, but at the same time lets you override each and any of them. A blitter transfers a rectangular area of the bitmap into a rectangular area of the screen. The meaning of various parameters is the following: • Source position: pixel coordinates of the upper left corner of the bitmap area, to be transferred. The default is the upper left corner of the bitmap. • Destination position: pixel coordinates within the target window of the upper left corner of the transferred area. The default is upper left corner of the window. • Area dimensions: the dimensions of the rectangular area to be transferred. The default is the dimensions of the bitmap. • Transfer mode. The way bitmap pixels are combined with existing window pixels. The default, SRCCOPY, copies the pixels over existing pixels. You may also specify more involved logical operations, like SRCAND (Boolean AND), SRCPAINT (Boolean OR), etc. (see your compiler's help on BitBlt). class Blitter { public: Blitter(Bitmap& bmp) : _bmp (bmp), _mode (SRCCOPY), _xDst (0), _yDst (0), _xSrc (0), _ySrc (0) { bmp.GetSize(_width, _height); } void SetMode(DWORD mode) { _mode = mode; } void SetDest(int x, int y) { _xDst = x; _yDst = y; } void SetSrc(int x, int y) { _xSrc = x; _ySrc = y; } void SetArea(int width, int height) { _width = width; _height = height; } // transfer bitmap to canvas void BlitTo(Canvas & canvas); private: Bitmap& _bmp; int _xDst, _yDst; int _xSrc, _ySrc; int _width, _height; DWORD _mode; }; The BlitTo method performs