How to set alpha to Volumetric LightScattering post-process

how can i set alpha to godrays when using Volumetric LightScattering post-process.
i just set the clear color of scene to transparent( scene.clearColor = new BABYLON.Color4(0,0,0,0):wink:
and then set the alphamode godrays.alphaMode = BABYLON.Engine.ALPHA_COMBINE
it seems that is not working at all (and it cause the renderer not clearing the color buffer i think)
so please give me a help.
thank you very much!

The post process buffer is not cleared when alpha mode is enabled. You can do it yourself:

godrays.onActivateObservable.add(() => {
    scene.getEngine().clear(scene.clearColor, scene._allowPostProcessClearColor, true, true);

However, I’m not sure I see any difference when alpha mode is enabled or not…

… and welcome to the forum!

1 Like

thanks for your replay, i find out that the alphaMode = ALPHA_COMBINE will not make the background transparent . if i use ALPHA_ADD the alpha will be ok but the other mesh material will also have alpha.
so do you konw why and how can i fix this?
The background of my project is i want the have some ar effect applied on my scene, so the post process should not make the background color become total black.


It seems you set alpha transparency on all your mesh: you should do it only on the “ray” mesh (meaning you need a different material for the ray and for the remaining mesh).

@Evgeni_Popov they are already using different material.

@Deltakosh any suggestion for this issue?

Let me ping @julien-moreau who is the creator of the godrays

thans @Deltakosh and @Evgeni_Popov, i just made a playground demo to show this issue more clear.
when use godrays the background will be black. and comment out the godrays will the the transparent background.

Try this:

I have set a picture in the canvas zone instead of a plain color to better see how it goes.

I have performed one minor change in each shader used by the effect: volumetricLightScatteringPassPixelShader and volumetricLightScatteringPixelShader. I have done it in an ugly way for the PG, I just updated the code in the Effect.ShaderStore object.

In godrays.onActivateObservable (line 58), you should set a clear color corresponding to the object emitting the god rays (that’s why I put (1,1,0) which is the emissive color you used for your cylinder).

I also had to access VolumetricLightScatteringPostProcess._volumetricLightScatteringRTT but as it is not exposed I simply used godrays._volumetricLightScatteringRTT. The onBeforeRenderObservable / onAfterRenderObservable observables clear the buffer to black by default, so I needed to remove them.

yes, i find almost the same way to chang the shader,and more ugly ,by changing the source code.

change the default 1 to 0 will solve my problem. and i think your solution is better then mine.

pg here


Putting 0 in the alpha component really disable most of the effect, that’s why in your PG you can see only the effect on a bit of the sphere: without the sphere you would not see any god rays.