How to extract bitmap from spritesheet in Win32 C++? - c++

Question

I'm trying to load individual cards from a spritesheet of cards based on suit and rank but I'm unsure of how to construct a new Bitmap object from cutting out Rectangle coordinates in the source image. I'm using <windows.h> currently and trying to find a simple way to accomplish this. I'm looking for something like this:
HBITMAP* twoOfHearts = CutOutFromImage(sourceImage, new Rectangle(0, 0, 76, 116));
From source: http://i.stack.imgur.com/WZ9Od.gif

Answer 1

Here's a function I played with the other week for more-or-less this same task. In my case, I wanted to return a HBRUSH that could be used with FillRect. In that instance, we still need to create a bitmap of the area of interest, before then going on to create a brush from it.
In your case, just return the dstBmp instead. spriteSheet is a global that has had a 256x256 spritesheet loaded. I've hardcoded the size of my sprites to 16x16, you'd need to change that to something like 81x117.
Here's some code that grabs a copy of the required area and some more that uses these 'stamps' to draw a level map. That said - there are all kinds of problems with this approach. Speed is one, excessive work is another one that impacts on the first. Finally, scrolling a window drawn like this produces artefacts.
// grabs a 16x16px section from the spriteSheet HBITMAP
HBRUSH getSpriteBrush(int col, int row)
{
HDC memDC, dstDC, curDC;
HBITMAP oldMemBmp, oldDstBmp, dstBmp;
curDC = GetDC(HWND_DESKTOP);
memDC = CreateCompatibleDC(NULL);
dstDC = CreateCompatibleDC(NULL);
dstBmp = CreateCompatibleBitmap(curDC, 16, 16);
int xOfs, yOfs;
xOfs = 16 * col;
yOfs = 16 * row;
oldMemBmp = (HBITMAP)SelectObject(memDC, spriteSheet);
oldDstBmp = (HBITMAP)SelectObject(dstDC, dstBmp);
BitBlt(dstDC,0,0,16,16, memDC, xOfs,yOfs, SRCCOPY);
SelectObject(memDC, oldMemBmp);
SelectObject(dstDC, oldDstBmp);
ReleaseDC(HWND_DESKTOP, curDC);
DeleteDC(memDC);
DeleteDC(dstDC);
HBRUSH result;
result = CreatePatternBrush(dstBmp);
DeleteObject(dstBmp);
return result;
}
void drawCompoundSprite(int x, int y, HDC paintDC, char *tileIndexes, int numCols, int numRows)
{
int mapCol, mapRow;
HBRUSH curSprite;
RECT curDstRect;
for (mapRow=0; mapRow<numRows; mapRow++)
{
for (mapCol=0; mapCol<numCols; mapCol++)
{
int curSpriteIndex = tileIndexes[mapRow*numCols + mapCol];
int spriteX, spriteY;
spriteX = curSpriteIndex % 16;
spriteY = curSpriteIndex / 16;
curDstRect.left = x + 16*mapCol;
curDstRect.top = y + 16 * mapRow;
curDstRect.right = curDstRect.left + 16;
curDstRect.bottom = curDstRect.top + 16;
curSprite = getSpriteBrush(spriteX, spriteY);
FillRect(paintDC, &curDstRect, curSprite);
DeleteObject(curSprite);
}
}
}
The latter function has since been replaced with the following:
void drawCompoundSpriteFast(int x, int y, HDC paintDC, unsigned char *tileIndexes, int numCols, int numRows, pMapInternalData mData)
{
int mapCol, mapRow;
HBRUSH curSprite;
RECT curDstRect;
HDC memDC;
HBITMAP oldBmp;
memDC = CreateCompatibleDC(NULL);
oldBmp = (HBITMAP)SelectObject(memDC, mData->spriteSheet);
for (mapRow=0; mapRow<numRows; mapRow++)
{
for (mapCol=0; mapCol<numCols; mapCol++)
{
int curSpriteIndex = tileIndexes[mapRow*numCols + mapCol];
int spriteX, spriteY;
spriteX = curSpriteIndex % mData->tileWidth;
spriteY = curSpriteIndex / mData->tileHeight
// Draw sprite as-is
// BitBlt(paintDC, x+16*mapCol, y+16*mapRow,
// mData->tileWidth, mData->tileHeight,
// memDC,
// spriteX * 16, spriteY*16,
// SRCCOPY);
// Draw sprite with magenta rgb(255,0,255) areas treated as transparent (empty)
TransparentBlt(
paintDC,
x+mData->tileWidth*mapCol, y+mData->tileHeight*mapRow,
mData->tileWidth, mData->tileHeight,
memDC,
spriteX * mData->tileWidth, spriteY*mData->tileHeight,
mData->tileWidth, mData->tileHeight,
RGB(255,0,255)
);
}
}
SelectObject(memDC, oldBmp);
DeleteObject(memDC);
}