[SDL] SDL_Cursor

[Bill Kendrick]

On Wed, Apr 09, 2003 at 02:41:45PM -0700, COSKU BAS wrote:
> does anyone know how to create a mouse cursor with an image
> file(bmp,png,jpg.....) ????
> 

I've only done it with XBMs (which I #include in my source),
but it shouldn't be too hard.

Just use SDL (for BMP) or SDL_Image (for PNG, JPG, ...) to load the file
into a SDL_Surface.

Then, use a routine to examine all of the pixels in the surface
and use them to generate a bitmap (and, probably also a bitmask) to send
to SDL_CreateCursor().


You could do something like:

  SDL_Surface * curosr_surf;
  Uint8 bitmap[128], bitmask[128];
  int width, height, x, y;
  Uint8 r, g, b, a;
  int bit, mask;
  Uint32 pix;

  ...


  /* Load the cursor into a surface: */

  cursor_surf = IMG_Load("cursor.png");
  ... test for errors! ...

  width = cursor_surf->w;
  height = cursor_surf->h;

  if (((width + 7) / 8) * height > 128)
    ... abort!  too big!


  for (i = 0; i < 128; i++)
  {
    bitmap[i] = 0;
    bitmask[i] = 0;
  }


  /* Create bitmap & bitmask based on the surface: */

  for (y = 0; y < height; y++)
  {
    for (x = 0; x < width; x++)
    {
      /* Get the pixel at (x,y): */

      pix = getpixel(cursor_surf, x, y);


      /* Determine RGB values of the pixel: */

      SDL_GetRGBA(cursor_surf, x, y, &r, &g, &b, &a);


      /* What's the mask color: */

      /* (Crappy threshold... you may want to do dithering or something...) */

      if (((r + g + b) / 3) > 128)
        map = 1;
      else
        map = 0;


      /* (Not sure if high alpha;mask=1...it'll be obvious if this is wrong) */
      /* (BTW, not all file formats support alpha/transparency, so
         you might need to determine mask based on some special 'colorkey'
         color, like "obnoxious purple" or something... How all of this
         map/mask decision stuff works depends on the image(s) you're loading,
         really.  Here, I'm making it generic, and assuming a format like
         PNG) */

      if (a > 128)
        mask = 1;
      else
        mask = 0;


      /* (This math could be wrong, but you get the idea :^) ) */

      bitmap[(x / 8) * y] |= (map >> (x % 8));
      bitmask[(x / 8) * y] |= (mask >> (x % 8));
    }
  }



Anyway, that's more-or-less how to do it.
It'd be nice if SDL had an "SDL_CreatCursorFromSurface()" function that
did the above for you.

:^/

-bill!

-- 
bill at newbreedsoftware.com                                            Hire me!
http://newbreedsoftware.com/bill/    http://newbreedsoftware.com/bill/resume/