GDI — Bitmaps & Device Contexts

HANDLE WINAPI LoadImageA(
    HINSTANCE hInst,   // ignored (pass NULL)
    LPCSTR    name,    // file path when LR_LOADFROMFILE is set
    UINT      type,    // must be IMAGE_BITMAP (0)
    int       cx,      // desired width (0 = use natural size)
    int       cy,      // desired height (0 = use natural size)
    UINT      fuLoad   // must include LR_LOADFROMFILE
);
// Returns HBITMAP cast to HANDLE, or NULL on error.
      

// Load from a relative path (backslash or slash both work)
HBITMAP hBackground = (HBITMAP)LoadImageA(
    NULL,
    "data\\background.bmp",   // or "data/background.bmp"
    IMAGE_BITMAP,
    0, 0,                       // 0,0 = keep natural size
    LR_LOADFROMFILE);

if (!hBackground) {
    OutputDebugString("Failed to load background.bmp");
    return FALSE;
}

// Load and scale to a specific size
HBITMAP hIcon = (HBITMAP)LoadImageA(
    NULL, "data\\icon.bmp",
    IMAGE_BITMAP, 32, 32,
    LR_LOADFROMFILE);
      

HBITMAP WINAPI CreateBitmap(
    int         nWidth,   // bitmap width in pixels
    int         nHeight,  // bitmap height in pixels
    UINT        nPlanes,  // colour planes (1 for RGB)
    UINT        nBitCount,// bits per pixel (8, 16, 24, or 32)
    const void* lpBits    // initial pixel data, or NULL for blank
);
      

// Create a 320×200 blank canvas
HBITMAP hCanvas = CreateBitmap(320, 200, 1, 32, NULL);
HDC     hdcCanvas = CreateCompatibleDC(NULL);
HGDIOBJ hOld = SelectObject(hdcCanvas, hCanvas);

// ... draw into hdcCanvas via SetPixel, StretchBlt, etc. ...

// Cleanup
SelectObject(hdcCanvas, hOld);
DeleteDC(hdcCanvas);
DeleteObject(hCanvas);
      

// ── Create ──
HBITMAP hBmp   = (HBITMAP)LoadImageA(NULL, "map.bmp",
                     IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);
HDC     hdcMem = CreateCompatibleDC(NULL);
HGDIOBJ hOld   = SelectObject(hdcMem, hBmp);   // select in

// ── Use ──
StretchBlt(hdcDest, 0, 0, 800, 600,
           hdcMem,  0, 0, 320, 200, SRCCOPY);

// ── Cleanup (always in this order) ──
SelectObject(hdcMem, hOld);  // restore previous selection first
DeleteDC(hdcMem);            // release DC
DeleteObject(hBmp);          // free surface
      

BOOL WINAPI StretchBlt(
    HDC   hdcDest,            // destination DC
    int   xDest, int yDest,   // destination top-left
    int   wDest, int hDest,   // destination size
    HDC   hdcSrc,             // source DC (must have bitmap selected)
    int   xSrc,  int ySrc,    // source top-left
    int   wSrc,  int hSrc,    // source size
    DWORD rop                 // raster op — only SRCCOPY supported
);
      

// 1. Copy a sprite (no scaling)
StretchBlt(
    hdcWindow, dstX, dstY, 64, 64,
    hdcSprites, spriteSheetX, spriteSheetY, 64, 64,
    SRCCOPY);

// 2. Scale up a 320×200 game canvas to fill an 800×600 window
StretchBlt(
    hdcWindow, 0, 0, 800, 600,
    hdcCanvas,  0, 0, 320, 200,
    SRCCOPY);

// 3. Copy a sub-region (source tile from a tileset)
int tileCol = 3, tileRow = 2;
int TILE = 32;
StretchBlt(
    hdcDest, screenX, screenY, TILE, TILE,
    hdcTiles, tileCol * TILE, tileRow * TILE, TILE, TILE,
    SRCCOPY);
      

// Read a pixel
COLORREF col = GetPixel(hdcMem, 10, 20);
if (col != CLR_INVALID) {
    BYTE r = GetRValue(col);
    BYTE g = GetGValue(col);
    BYTE b = GetBValue(col);
}

// Write pixels — simple flood-fill loop
for (int y = 0; y < 16; y++) {
    for (int x = 0; x < 16; x++) {
        SetPixel(hdcCanvas, x, y, RGB(255, 0, 0));  // red square
    }
}

// Colour constant examples
COLORREF red    = RGB(255,   0,   0);
COLORREF green  = RGB(  0, 255,   0);
COLORREF blue   = RGB(  0,   0, 255);
COLORREF white  = RGB(255, 255, 255);
COLORREF black  = RGB(  0,   0,   0);
COLORREF yellow = RGB(255, 255,   0);
      

BITMAP bm;
if (GetObjectA(hBmp, sizeof(bm), &bm)) {
    printf("Width=%ld Height=%ld BPP=%d\n",
           bm.bmWidth, bm.bmHeight, bm.bmBitsPixel);
}