Turn PNG loading code to use a FILE instead of local resource

Question

I'm working on a little softare which is meant to display a png file directly on the desktop. i've found a way of doing the later part with a HBITMAP strukture. Yet I've spent days by now searching for a way to load a .PNG file to such a HBITMAP.

The code I found eventuall (which I also could compile) was this one from this page:

http://logiklabs.tumblr.com/post/22946728048/how-to-load-an-image-resource-into-a-hbitmap

Think it would work perfectly. My problem is though that this one is meant to use already attached .png files.

Yet I need the possibility to use at runtime a file from an (at compile time) unknown location.

So how could I alter that script to achieve that? My C++ knowledge is not the best unfortunately and the MS-documentation of thsoe related functions did not really help either :/

I'd be very very thankful!

Answer 1

It looks like you can just load the PNG file into RAM and pass its address and length to stbi_load_from_memory(). You basically change the first part of the code on the linked page to load the file into RAM, then proceed the same. Example below:

static HBITMAP LoadImageResource(LPCTSTR filename)
{
    unsigned char *res_data, *splash_image;
    DWORD res_size;
    int width, height, components;
    BITMAPV5HEADER bmh;
    HBITMAP hBitmapRet;
    FILE* f = _tfopen(filename, "rb");

    if (!f)
        return NULL;

    fseek(f, 0, SEEK_END);
    res_size = ftell(f);
    rewind(f);

    res_data = new unsigned char[res_size];
    fread(res_data, sizeof(unsigned char), res_size, f);
    fclose(f);

    splash_image = stbi_load_from_memory(res_data, res_size, &width, &height, &components, 0);

    ZeroMemory(&bmh, sizeof(BITMAPV5HEADER));
    bmh.bV5Size = sizeof(BITMAPV5HEADER);
    bmh.bV5Width = width;
    bmh.bV5Height = -height;
    bmh.bV5Planes = 1;
    bmh.bV5BitCount = 32;
    bmh.bV5Compression = BI_BITFIELDS;
    bmh.bV5RedMask = 0x00FF0000;
    bmh.bV5GreenMask = 0x0000FF00;
    bmh.bV5BlueMask = 0x000000FF;
    bmh.bV5AlphaMask = 0xFF000000;

    hBitmapRet = CreateDIBitmap(GetDC(NULL), (BITMAPINFOHEADER *) &bmh, CBM_INIT,
                    splash_image, (BITMAPINFO *) &bmh, DIB_RGB_COLORS);

    stbi_image_free(splash_image);
    delete[] res_data;
    return hBitmapRet;
}