Unity Issue Tracker - Graphics.Blit in OnRenderImage always causes a warning on entering Play mode when writing to a RenderTexture variable last

By Design

Votes

Found in

Issue ID

Regression

Graphics.Blit in OnRenderImage always causes a warning on entering Play mode when writing to a RenderTexture variable last

Sep 19, 2017

Steps to reproduce:
1.Open attached “WriteWarning.zip” Unity project
2.Open ‘test’ scene
3.Enter Play mode

Expected results:
No warning is given
Actual results:
'OnRenderImage() possibly didn't write anything to the destination texture!’ warning is given

Reproduced in: 2017.3.0b2, 2017.2.0f1, 2017.1.1p3, 5.6.3p4, 5.5.4p5, 5.5.0b3

Note: Even though the warning is given, the texture is always written

Resolution Note (2018.1.X):

Hello, this is by design. As written in the doc you're expected to render into the destination texture as it'll be the one used as a source for the rest of the render chain. It still works if you don't because there's a fail-safe in the engine but it will issue a warning as this is bad practice.

spajus

Jul 29, 2020 14:07

To help you out, this happens when OnRenderImage(source, destination) does not have active render texture set to "destination". For example if you do Graphics.Blit into somewhere else (downscaled copy of destination for example), active render texture will become that downscaled copy. One workaround is to do RenderTexture.active = destination in the end of your OnRenderImage, and make sure it does not return early.

Nobody will fix this issue because they closed it as "by design". For Unity team: it would be super useful is to include the actual active render texture name, expected render texture (destination) name and camera name in the warning message.
abishekhparivel

Jul 22, 2020 12:22

sorry got it
abishekhparivel

Jul 22, 2020 12:21

I am still getting this issue on 2019.3.12f1
AwesomeAlexx

Jan 30, 2020 15:17

I'm facing the same issue on 2019.2.17f1.

I have this warning :
"OnRenderImage() possibly didn't write anything to the destination texture!"

Note: Even though the warning is given, the texture seems to always be written
RendCycle

Jul 05, 2018 13:19

Console Warning message is still present in Unity 2018.1.6f1.