Depth Test and Depth Write

Enabling or Disabling the Depth Buffer

By default, Panda3D renders the render scene graph with Z-buffering enabled. This technique makes it possible to render overlapping geometry in arbitrary order without having rear surfaces appear on top of front surfaces. It is possible to disable the depth buffer or alter its behavior.

In the 2D scene graph render2d, the depth buffer is disabled by default, because it is used for GUI and not for self-overlapping 3D models. But in rare cases, it is desirable to show 3D models in the 2D scene graph, so it is possible to enable the depth buffer for those models specifically.

The most common thing to want to do is to disable the depth-write. This means that geometry will still be tested against the depth buffer, but it will not affect the depth buffer. This is often used when rendering objects such as particles that are transparent. To disable or enable the depth-write, use:

nodePath.setDepthWrite(False)  # Disable
nodePath.setDepthWrite(True)   # Enable

It may also be desirable to disable the depth-test. This means that the geometry pays no attention whatsoever to the contents of the depth-buffer. This is often used for rendering things like heads-up displays, which have no relation to the 3D depth of the scene. To disable or enable the depth-test, use:

nodePath.setDepthTest(False)  # Disable
nodePath.setDepthTest(True)   # Enable

Note

Disabling the depth-test with setDepthTest(False) also implicitly disables depth-writes, regardless of the current depth-write setting. This is because the graphics hardware ties both behaviors to the same comparison function: turning the comparison off disables writes as a side effect. If you want geometry to continue writing to the depth buffer while ignoring the existing depth values, leave depth-test enabled and instead use DepthTestAttrib with M_always (see below), which always passes the test but still allows depth-writes to occur.

One can remove these settings using clearDepthTest() and clearDepthWrite().

Altering the Depth Buffer

Occasionally, it is desirable to alter the functionality of the depth buffer. Normally, the depth buffer only renders things that are in front, but it can be made to render things that are in back, or equal. This is rarely used, but it can be important for certain unusual algorithms like shadow volumes.

To do this, you need to use the DepthTestAttrib directly, in one of the following variants:

nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MNone))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MNever))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MLess))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MEqual))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MLessEqual))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MGreater))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MGreaterEqual))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MNotEqual))
nodePath.setAttrib(DepthTestAttrib.make(RenderAttrib.MAlways))

The M_none mode is equivalent to calling setDepthTest(False) and, as noted above, disables depth-writes as well. To keep depth-writes active while having the depth test unconditionally pass, use M_always instead: this configures the comparison to succeed for every fragment, so the depth buffer will still be updated if depth-write is enabled.

Depth Sorting

When turning depth test off, it is sometimes desirable to use depth sorting instead. Depth sorting is controlled by the culling system, which can be controlled by the CullBinAttrib.

Transparency

Certain settings of the TransparencyAttrib can also affect the depth-test.