/* 
 *  call-seq:
 *     blit(target,dest,source=nil)  ->  Rect
 *
 *  Blit (copy) all or part of the surface's image to another surface,
 *  at a given position. Returns a Rect representing the area of 
 *  +target+ which was affected by the blit.
 *
 *  This method takes these arguments:
 *  target:: the target Surface on which to paste the image.
 *  dest::   the coordinates of the top-left corner of the blit. Affects the
 *           area of +other+ the image data is /pasted/ over.
 *           Can also be a Rect or an Array larger than 2, but
 *           width and height will be ignored. 
 *  source:: a Rect representing the area of the source surface to get data
 *           from. Affects where the image data is /copied/ from.
 *           Can also be an Array of no less than 4 values. 
 */
VALUE rbgm_surface_blit(int argc, VALUE *argv, VALUE self)
{
        int left, top, right, bottom;
        int blit_x,blit_y,blit_w,blit_h;
        //int dest_x,dest_y,dest_w,dest_h;
        int src_x,src_y,src_w,src_h;
        VALUE returnrect;
        SDL_Surface *src, *dest;
        SDL_Rect *src_rect, *blit_rect;

        VALUE vtarget, vdest, vsource;

        rb_scan_args( argc, argv, "21", &vtarget, &vdest, &vsource );

        Data_Get_Struct(self, SDL_Surface, src);
        Data_Get_Struct(vtarget, SDL_Surface, dest);

        vdest = convert_to_array(vdest);
        blit_x = NUM2INT(rb_ary_entry(vdest,0));
        blit_y = NUM2INT(rb_ary_entry(vdest,1));

        /* did we get a src_rect argument or not? */
        if( !NIL_P(vsource) )
        {
                /* it might be good to check that it's actually a rect */
                vsource = convert_to_array(vsource);
                src_x = NUM2INT( rb_ary_entry(vsource,0) );
                src_y = NUM2INT( rb_ary_entry(vsource,1) );
                src_w = NUM2INT( rb_ary_entry(vsource,2) );
                src_h = NUM2INT( rb_ary_entry(vsource,3) );
        }
        else
        {
                src_x = 0;
                src_y = 0;
                src_w = src->w;
                src_h = src->h;
        }
        src_rect = make_rect( src_x, src_y, src_w, src_h );

        /* experimental (broken) rectangle cropping code */
        /* crop if it went off left/top/right/bottom */
        //left = max(blit_x,0);
        //top = max(blit_y,0);
        //right = min(blit_x+src_w,dest->w);
        //bottom = min(blit_y+src_h,dest->h);

        left = blit_x;
        top = blit_y;
        right = blit_x+src_w;
        bottom = blit_y+src_h;
                
        //blit_w = min(blit_x+blit_w,dest->w) - max(blit_x,0);
        //blit_h = min(blit_y+blit_h,dest->h) - max(blit_y,0);
        blit_w = right - left;
        blit_h = bottom - top;
        
        blit_rect = make_rect( left, top, blit_w, blit_h );

        SDL_BlitSurface(src,src_rect,dest,blit_rect);

        returnrect = rb_funcall(cRect,rb_intern("new"),4,
                                INT2NUM(left),INT2NUM(top),\
                                INT2NUM(blit_w),INT2NUM(blit_h));

        free(blit_rect);
        free(src_rect);
        return returnrect;
}