In A4 it was possible to use blit() or simply the drawing primitives to paint 255,0,255 on a bitmap to make specific areas transparent and then showing the modified bitmap with masked_blit() or draw_sprite().
How do I do this in A5? I have a bitmap, I want to add transparent pixels to it (or remove existing pixels). When I use al_draw_pixel(x,y, al_map_rgba(255,0,255,255)) nothing is added to the bitmap since the color of the added pixel is transparent. Is there something similar to al_remove_pixel(), al_force_drawing_to_bitmap() or some other procedure to do this?
Hope I explained it in a way you get what I want to do. Otherwise I'll have to draw some pictures.