Designing Games with Game Maker - YoYo Games

Starting 3D mode will result in the following changes. First of all hidden surface removal is
switched on (using a 16-bit z-buffer). This means that for each pixel on the screen only the
drawing with the smallest z-value (= depth value) is drawn. If instances have the same depth
it is unclear what will happen and you can get ugly effects. Make sure instances that might
overlap do not have the same depth value!
Secondly, the normal orthographic projection is replaced by a perspective one. This means the
following. Normally the size of instances on the screen is independent on its depth. With a
perspective projection instances that have a greater depth will appear smaller. When the
depth is 0 it is equal to the old size (unless you change the projection; see below). The
viewpoint for the camera is placed at a distance above the room. (This distance is equal to the
width of the room; that gives a reasonable default projection.) Only instances in front of the
camera are drawn. So don't use instances with a depth smaller than 0 (or at least not smaller
than -w where w is the width of the room or the view).
Thirdly, the vertical y-coordinate is reversed. While normally the (0,0) position is at the top-
left of the view, in 3D modo the (0,0) position is at the bottom-left position, as is normal for
3-dimensional views.
You can actually switch hidden surface remove and perspective projection on or off using the
following functions.
d3d_set_hidden(enable) Enables hidden surface removal (true) or
disables it (false).
d3d_set_perspective(enable) Enables the use of a perspective
projection (true) or disables it (false).
Easy drawing
Once 3D mode has been switched on you can use Game Maker as you are used to it (except
for the remarks made at the beginning). Only objects will appear in different sizes based on
their depth setting. You can even use views. One additional function can be useful. If you draw
a number of things in a piece of code you might want to change the depth value between the
primitives you draw. For this you use:
d3d_set_depth(depth) Sets the depth used for drawing.