3D mode

3D mode is the term used when Game Maker's 3D engine is turned on using d3d_start.

Going to 3D mode
Starting 3D mode will result in the following changes:

Hidden surface removal
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) is drawn.

Perspective projection
The normal orthographic projection is replaced by a perspective one. An orthographic projection means that the size of instances on the screen is independent of their depth. With a perspective projection instances that have a greater depth will appear smaller. With the default projection, a depth of 0 is equal to the original size.

The viewpoint for the camera is by default placed at a distance above the room equal to the width of the room. Only instances in front of the camera are drawn. So don't use instances with a depth smaller than the width of the room. (or the view, if enabled)

Reversed y-coordinate
The vertical y-coordinate is reversed. This means that the (0,0) position is at the bottom-left position, instead of the top-left position. This is normal for 3D graphics.

Disabled features
Once 3D mode has been switched on you can use Game Maker as you are used to it, except for a few things: All other features work completly, you can even use views.
 * Particles are disabled in 3D mode.
 * Surfaces cannot be used.
 * Transitions