| textureName | The name of the Terrain texture to copy into. |
| textureIndex | The index of the Terrain texture to copy into. |
| sourceRect | The part of the active Render Texture to copy. |
| dest | The X and Y coordinates of the Terrain texture to copy into. |
| allowDelayedCPUSync | Specifies whether to allow delayed CPU synchronization of the texture. |
Copies the specified part of the active RenderTexture to the Terrain texture.
If the allowDelayedCPUSync parameter is set to true, and the platform supports copying between a RenderTexture and a Texture2D, Unity performs a GPU copy from the active RenderTexture to the Terrain texture. This is sufficient for Terrain rendering, but you will need to call SyncTexture afterward to synchronize the CPU part of the texture.
If the allowDelayedCPUSync parameter is set to false, or the platform doesn't support copying between textures, Unity immediately reads back the content of the active RenderTexture, and updates both the CPU and GPU parts of the Terrain texture.
Unity recommends you create the source Render Texture to copy in the format that Terrain.heightmapRenderTextureFormat specifies, and call the HLSL function PackHeightmap before you write to the source render texture. To use PackHeightmap, make sure you have the include directive #include "UnityCG.cginc" in your shader.
Additional resources: DirtyTextureRegion, SyncTexture.