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Texture Buffer Depth Fast Node
Texture buffers are 2D textures used to build a deferred image for various post-effects. To sample data from such a texture connect it to the Sample Texture node and specify UV coordinates for reading texels from the texture.
This 2D Texture contains camera-to-surface distances of opaque materials. Unlike the Texture Buffer Depth this buffer has a lower accuracy but has mip levels.
This buffer is preferred for complex post-effects with multiple depth reading operations, as reading can be performed from a mipmap instead of full resolution.