Depth:
Turn on Depth to create a depth channel. Strokes appear on top of previously painted strokes when Depth is OFF.

In the scene, turn on Depth for more realistic natural effects (for example, for plants, fire, water). This should also prevent unusual results. By default, depth is forced on in the scene (see Force Depth).

Note :
Paint Effects may run slightly faster when Depth is turned off.

Modify Depth:
Depth must be turned on to use this option. Turn on Modify Depth to paint to the depth channel. If a stroke has a depth channel, but Modify Depth is off, the stroke appears behind strokes that are nearer in the scene.

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