This function can be used to toggle alpha-blending on and off. Basically, if you have this set to false, all images being drawn will be drawn 100% opaque, meaning that any transparent, or semi transparent, areas of a sprite or background will be visible as a solid colour. It is a good idea to have alpha blending off whenever possible (especially when developing for mobile devices) as this greatly increases the draw speed.
Argument Description enable Enable or disable alpha blending value (true or false).
draw_sprite(spr_Background, 0, 0, 0);
The above code switches off alpha blending to draw a background sprite and then switches it back on again to continue drawing.