Designing Games with Game Maker - YoYo Games

draw_set_blend_mode(mode) Indicates what blend mode to use. The
following values are possible: bm_normal, bm_add, bm_subtract, and
bm_max. Don't forget to reset the mode to normal after use because otherwise
also other sprites and even the backgrounds are drawn with the new blend
mode.
draw_set_blend_mode_ext(src,dest) Indicates what blend mode to use
for both the source and destination color. The new color is some factor times
the source and another factor times the destination. These factors are set with
this function. To understand this, the source and destination both have as red,
green, blue, and alpha component. So the source is (Rs, Gs, Bs, As) and the
destination is (Rd, Gd, Bd, Ad). All are considered to lie between 0 and 1. The
blend factors you can choose for source and destination are:
• bm_zero: Blend factor is (0, 0, 0, 0).
• bm_one: Blend factor is (1, 1, 1, 1).
• bm_src_color: Blend factor is (Rs, Gs, Bs, As).
• bm_inv_src_color: Blend factor is (1–Rs, 1–Gs, 1–Bs, 1–As).
• bm_src_alpha: Blend factor is (As, As, As, As).
• bm_inv_src_alpha: Blend factor is (1–As, 1–As, 1–As, 1–As).
• bm_dest_alpha: Blend factor is (Ad, Ad, Ad, Ad).
• bm_inv_dest_alpha: Blend factor is (1–Ad, 1–Ad, 1–Ad, 1–Ad).
• bm_dest_color: Blend factor is (Rd, Gd, Bd, Ad).
• bm_inv_dest_color: Blend factor is (1–Rd, 1–Gd, 1–Bd, 1–Ad).
• bm_src_alpha_sat: Blend factor is (f, f, f, 1); f = min(As, 1–Ad).
For example, the normal blending mode sets the source blending to
bm_src_alpha and the destination blending to bm_inv_src_alpha. Don't forget
to reset the mode to normal after use because otherwise also other sprites and
even the backgrounds are drawn with the new blend mode.
Drawing texture primitives is a bit of work but can lead to great results. You can even use it to
make fake 3D games.
Drawing Surfaces
This functionality is only available in the Pro Edition of Game Maker.