Question

I’ve searched around using google but I’m completely confused on how to load an image (PNG in my case) from resource and then converting it to a bitmap in memory for use in my splash screen. I’ve read about GDI+ and libpng but I don’t really know how to do what I want. Could anyone help?

Answer 1

I ended up using PicoPNG to convert the PNG to a two dimensional vector which I then manually contructed a bitmap from. My final code looked like this:

HBITMAP LoadPNGasBMP(const HMODULE hModule, const LPCTSTR lpPNGName)
{
    /* First we need to get an pointer to the PNG */
    HRSRC found = FindResource(hModule, lpPNGName, "PNG");
    unsigned int size = SizeofResource(hModule, found);
    HGLOBAL loaded = LoadResource(hModule, found);
    void* resource_data = LockResource(loaded);

    /* Now we decode the PNG */
    vector<unsigned char> raw;
    unsigned long width, height;
    int err = decodePNG(raw, width, height, (const unsigned char*)resource_data, size);
    if (err != 0)
    {
        log_debug("Error while decoding png splash: %d", err);
        return NULL;
    }

    /* Create the bitmap */
    BITMAPV5HEADER bmpheader = {0};
    bmpheader.bV5Size = sizeof(BITMAPV5HEADER);
    bmpheader.bV5Width = width;
    bmpheader.bV5Height = height;
    bmpheader.bV5Planes = 1;
    bmpheader.bV5BitCount = 32;
    bmpheader.bV5Compression = BI_BITFIELDS;
    bmpheader.bV5SizeImage = width*height*4;
    bmpheader.bV5RedMask = 0x00FF0000;
    bmpheader.bV5GreenMask = 0x0000FF00;
    bmpheader.bV5BlueMask = 0x000000FF;
    bmpheader.bV5AlphaMask = 0xFF000000;
    bmpheader.bV5CSType = LCS_WINDOWS_COLOR_SPACE;
    bmpheader.bV5Intent = LCS_GM_BUSINESS;
    void* converted = NULL;
    HDC screen = GetDC(NULL);
    HBITMAP result = CreateDIBSection(screen, reinterpret_cast<BITMAPINFO*>(&bmpheader), DIB_RGB_COLORS, &converted, NULL, 0);
    ReleaseDC(NULL, screen);

    /* Copy the decoded image into the bitmap in the correct order */
    for (unsigned int y1 = height - 1, y2 = 0; y2 < height; y1--, y2++)
        for (unsigned int x = 0; x < width; x++)
        {
            *((char*)converted+0+4*x+4*width*y2) = raw[2+4*x+4*width*y1]; // Blue
            *((char*)converted+1+4*x+4*width*y2) = raw[1+4*x+4*width*y1]; // Green
            *((char*)converted+2+4*x+4*width*y2) = raw[0+4*x+4*width*y1]; // Red
            *((char*)converted+3+4*x+4*width*y2) = raw[3+4*x+4*width*y1]; // Alpha
        }

    /* Done! */
    return result;
}