深度渲染纹理格式。
Depth format is used to render high precision "depth" value into a render texture. Which format
is actually used depends on the platform. On OpenGL it is the native "depth component" format
(usually 24 or 16 bits), on Direct3D9 it is the 32 bit floating point ("R32F") format. When writing
shaders that use or render into a depth texture, care must be taken to ensure that they work both
on OpenGL and on Direct3D, see depth textures documentation.
请注意，并非所有显卡都支持深度纹理。请使用 SystemInfo.SupportsRenderTextureFormat
检查支持情况。
另请参阅：RenderTexture.format、RenderTexture 类、SystemInfo.SupportsRenderTextureFormat。