iOS RenderTexture is cleared before CommandBuffer.DrawMesh

Unity Engine
,
1

I have a persistent RGBA32 render texture that I am drawing a few pixels of each frame (Using CommandBuffer.DrawMesh and a custom mesh). On iOS Metal, this does not work as the render texture seems to be cleared without my consent before drawing to it.

I can however blit to the whole texture and discard the pixels I don’t need, and that fixes the issue. But this is bad performance-wise, adding 1ms due to shader complexity.

Any ideas how to get the contents of a rendertexture to stick around while drawing to small portions of it? I don’t think I’ve seen this behaviour documented anywhere. It is only an issue on iOS Metal (having tried Android, PC, WebGL, MacOS, iOS GLES3). I am currently on 2019.3.15f1, and using the standard rendering pipeline.

Thank you!

2

Ok, figured out the problem: it was simply that I was calling

SetRenderTarget(writeTo, RenderBufferLoadAction.DontCare,
                RenderBufferStoreAction.Store);

instead of :

SetRenderTarget(writeTo, RenderBufferLoadAction.Load,
                RenderBufferStoreAction.Store);

and iOS is the only platform that cares about that.