Is there a public API or recommend way to get a camera's colorBuffer?

FBplus · March 12, 2021, 2:21pm

I know we can create a new camera and bind a renderTexture on it so we can get what that camera is rendering,or add a posteffect on the camera and use camera.postEffects._sourceTarget.colorBuffer.
But is there a better way or recommend method to achieve this?

mvaligursky · March 12, 2021, 2:37pm

So what are you trying to do with the colorBuffer?
There’s a way to get it for something like this: http://playcanvas.github.io/#graphics/grab-pass.html

FBplus · March 12, 2021, 4:18pm

Hi,@mvaligursky ,thanks so much for your reply

I am trying to make a bloom effect only on specific objects according your advice here:

So I have to capture the camera’s colorbuffer before the bloom objects is rendered. I’ve managed to achieve that effect but wonder if there is any better solution?
I’ve tried to use texture_grabPass to replace camera.postEffects._sourceTarget.colorBuffer,but I can not capture anything,Is there any pre setup need to be done?

The test project can be found here:
https://playcanvas.com/project/773988/overview/selective-bloom

mvaligursky · March 12, 2021, 4:43pm

the key to grab pass is that you need to have a shader that uses texture_grabPass uniform … we detect the shader needs grab pass texture, and before the object is rendered, we grab the backbuffer and copy it to texture.

github.com

playcanvas/engine/blob/aae0968f5c862b83f316404d1b728fcb1d8ef693/examples/graphics/grab-pass.html#L48


        texCoord = aUv;
    }
</script>
<script id="fshader" type="x-shader/x-fragment">
    precision mediump float;
    // use the special texture_grabPass texture, which is a built-in texture. Each time this texture is used
    // for rendering, the engine will copy color framebuffer to it which represents already rendered the scene
    uniform sampler2D texture_grabPass;
    // normal map providing offsets
    uniform sampler2D uOffsetMap;
    // engine built-in costant storing render target size in .xy and inverse size in .zw
    uniform vec4 uScreenSize;
    varying vec2 texCoord;
    void main(void)

So I guess to use this, the first postprocessing shader that needs to use backbuffer needs to have this uniform.

FBplus · March 12, 2021, 5:08pm

I’ve added that uniform to the shader defination but it seems I still can not get the right colorbuffer.I used an Image to show the texture,as you can see on the top left of the screen,the texture caputured is pure black.

use camera.postEffects._sourceTarget.colorBuffer:

use texture_grabPass:

mvaligursky · March 12, 2021, 5:23pm

At what time in the frame do you use that grab texture? Is anything in the framebuffer at that point?
I’d suggest to use debug engine (tick debug when launching in the editor), and capture the frame in SpectorJS … you can see when the grab pass runs and what is in target and similar. That could give you a help with the debugging of this.