ASM Community

You should look up CreateCompatibleDC, CreateDIBSection and SelectObject. I can post some (ugly!) C source code if you'd like me to, which works. Or should work. Well, it's used in a commercial project, so it had better work ;-).

okay, you asked for it :) It is for 32bpp (though by changing "a few things", you should be able to make it work for any resolution). After you have created the drawbuf, you can access drawbuf->buf directly. When done with your changes, blit the bitmap to screen the usual way.

typedef struct _DrawBuf {
	int		w;
	int		h;
	unsigned int*	buf;
	BITMAPINFO	bmp;
	HBITMAP		hbmp;
	HDC		hdcbmp;
} DrawBuf;


static bool createDrawBuf(DrawBuf *db, int width, int height)
{
	memset(db, 0, sizeof(*db));
	db->w = width;
	db->h = height;

	db->bmp.bmiHeader.biBitCount = 32;

	// no colorTable since we're doing 32bpp.
	db->bmp.bmiHeader.biClrImportant = 0;
	db->bmp.bmiHeader.biClrUsed = 0;

	db->bmp.bmiHeader.biCompression = BI_RGB;

	// biHeight must be negative so we get a top-down bitmap. Fucked up MS.
	db->bmp.bmiHeader.biHeight = 0 - (db->h);

	db->bmp.bmiHeader.biPlanes = 1;
	db->bmp.bmiHeader.biSize = sizeof(db->bmp.bmiHeader);
	db->bmp.bmiHeader.biSizeImage = db->w * db->h * 4;
	db->bmp.bmiHeader.biWidth = db->w;

	db->hdcbmp = CreateCompatibleDC(NULL);
	if(db->hdcbmp == NULL) return false;

	db->hbmp = CreateDIBSection(db->hdcbmp, &db->bmp, DIB_RGB_COLORS, (void **) &db->buf, NULL, 0);
	if(db->hbmp == NULL) return false;

	SelectObject(db->hdcbmp, db->hbmp);

	return true;
}


static void killDrawBuf(DrawBuf *db)
{
	DeleteObject(db->hbmp);
	DeleteDC(db->hdcbmp);
	memset(db, 0, sizeof(*db));
}

The way I do it is to draw in "gfxboard.buf", which is pretty easy. And then use a bitblt to display on screen. This means that you'll have to bitblt every time you have made changes (not per pixel please, but after all changes are done). This approach requires you to handle all (re)drawing of the area where you want to show the image. If you'd rather have a "normal" bitmap where windows handles the updating (good for a bitmap you don't change very often), you should probably use another technique. I hate working with bitmaps under windows :)