Day: January 8, 2015

Actually, GdkPixbuf is a two dimensional array by itself, so we do not need waterfall[i][j] anymore. A single line buffer, waterfall2[j], will suffice.

   for(int i=0; i<2;i++) {
     p = gdk_pixbuf_get_pixels(pixbuf) + (iwater + i * WATERFALL_YSIZE) * rowstride;
     for(int j=0;j<WATERFALL_XSIZE;j++) {
       double tmp = waterfall2[j];
       *p++ = colormap_r(tmp);
       *p++ = colormap_g(tmp);
       *p++ = colormap_b(tmp);
     }
   }
    
  background = gdk_pixbuf_new (GDK_COLORSPACE_RGB, FALSE, 8, WATERFALL_XSIZE, WATERFALL_YSIZE);

  scale_x     =   3.0;
  scale_y     =   1.0;
  offset_x    =   0;  
  offset_y    =  -(iwater+1);
  dest_x      =   0;  
  dest_y      =   0;  
  dest_width  =   w;  
  dest_height =   WATERFALL_YSIZE;
  gdk_pixbuf_composite(pixbuf, background, dest_x, dest_y, dest_width, dest_height, offset_x, offset_y, scale_x, scale_y, GDK_INTERP_BILINEAR, 255);

  iwater++;
  if (iwater >= WATERFALL_YSIZE) iwater = 0;

In the first step, pixbuf, which is twice as large as minimally required, is updated in two locations. This is a redundant operation, but in this way, a scroll up is implemented with a single copy, gdk_pixbuf_composite().