Render vertex color and albedo

bethleem

The setup is: one single scene with one copy of each object in it. Each object has a mesh. This mesh has a texture and also has vertex color information different as the one from the texture. The goal is some method that allows to compose a final render with: 1) a pass that render the albedos (textures) in a viewport (easy, is the deafult behaviour). 2) a second pass who renders not the albedos but the vertex colors of the meshes in order to do some calculations over them and add some details to the final render. It needs to be done over the viewport becasuse this details are view-dependent. (Something like but no quite this: https://twitter.com/georgebatch/status/1040996814202318848 )

Is this even possible in godot? I was trying some aprroaches but did not get how to access the mesh-vertex-color info once it has render the albedo in the first pass. Same if I render first the vertex color, then I´m not able to access the albedo. Any ideas?

Thx!

cybereality

You can do this with a custom shader. Here is an example that just renders the vertex color.

shader_type spatial;
render_mode unshaded;

void fragment() {
	ALBEDO = COLOR.rgb;
}

On the last line (in the fragment/pixel shader) the ALBEDO out parameter is what sets the color on the screen. In the code example, I am just setting it to the vertex color. But you can sample the texture and then multiply it by the vertex color to combine them (or some other math, whatever you want).

shader_type spatial;
render_mode unshaded;

uniform sampler2D texture_map;

void fragment() {
	ALBEDO = COLOR.rgb * texture(texture_map, UV).rgb;
}

Here this is a ShaderMaterial and you would set the texture on the shader param section.

bethleem

Thanks :) but I already try that. In yor example the calculations are made per object. I needed it to be done per frame, interobjects and view dependant.

Megalomaniak

So apply the same shader material to multiple objects.

bethleem

@Megalomaniak said: So apply the same shader material to multiple objects.

But I can´t access one object vertex info from another object shader...

The solution should be in the render (camera). Problem seem to be Godot only allows to read the albedo OR vertex color of each object from the camera, not both. I´m asking for a trick to read both from a render (camera) instance. A trick that will not involve duplicate all the scene objects with differente shader material, one per vertex and another for albedo.

xyz

Render passes into separate viewports and then composit them in main viewport using canvas item shader.

Megalomaniak

Yeah what @xyz said - this is not a new problem, but do note that the solution to it involves working with data 1 frame behind the current game state. That really is the only way to solve it btw. At least as far as I'm aware. You can't render ahead what has not happened yet. Not in an interactive medium anyways.

cybereality

Reading your original post again, I think you can do this with a single shader like the code I posted. If you need view-dependent behavior, you could pass the camera transform as a uniform parameter to the shader. But this wouldn't quite work for certain post-processing effects (it depends what you are doing, maybe you can explain more) but you might be able to composite both the shader material and a canvas shader on top (for example if you need outlines). I think if you could better explain what you are trying to do, it might help.

xyz

I too think this is probably doable in a single shader. But in order to suggest anything specific, as @cybereality already said, we'll need to know precisely what kind of view dependent effect you're after @bethleem