Applying “nearest neighbor” filtering to a baked lightmap UV2 texture

Help Shaders
1

Godot Version

4.2

Question

Suppose you’re doing something Quake I/II inspired - low-poly models, pixelated textures. Perhaps you’d also like pixelated baked lightmaps (LightmapGI) to match? But the matter is complicated.

For my own samplers I can do

uniform sampler2D my_texture : filter_nearest;

but for built-ins the matter is complicated - I can’t even find what the lightmap sampler is named in the GLSL source code, let alone whether I can modify it from the Godot’s shader language. It’s not even influenced by the light() function, it just does its own thing somewhere. And I can’t view the generated GLSL (?) so I can’t tell what it’s doing and how.

I can somewhat match the effect by converting the EXR (which is a sampler2D-incompatible (?) Texture2DArray) to a PNG and writing a shader that mimics the lightmap_uv_rect transform,

shader_type spatial;
render_mode unshaded;
uniform sampler2D SHADOW_ATLAS : filter_nearest;
uniform vec4 lightmap_uv_rect;
void fragment() {
	ALBEDO = texture(SHADOW_ATLAS, UV2*lightmap_uv_rect.zw).xyz;
}

a screenshot of the scene with shader in action. UV rectangle is filled out by hand in Inspector
a screenshot of the scene with shader in action. UV rectangle is filled out by hand in Inspector1920×1200 506 KB

But this introduces no less than a few issues:

  • The build now contains a duplicate texture (and these are pretty big even for small scenes)
  • The texture has to be updated separately after baking (which will require an extra user interaction).
  • The texture extents also have to be updated separately.
  • Whatever material math has to be re-created from scratch - it’s not even just that EXR is stored in HDR, something’s missing
  • Since we’re setting the albedo color, this affects subsequent baking - the shader has to be disabled before doing so
  • Probably even more wonderful things I’m yet to notice.

For the time I have settled on just not going for this visual style as result, but it’d be nice to know for future reference.

Note: I have originally posted this question on Godot Q&A, where it has received no responses and was locked and unlisted after migration

2

The lightmap texture is a Texture2DArray so you need to use a sampler2DArray uniform in your shader to be able to use it.

It’s pretty hidden but you can view the native GLSL code generated by your material. Open the ShaderMaterial in the inspector, click in the icon with a screwdriver and a span and click on Inspect Native Shader Code:

image
image582×700 50.8 KB

I don’t know about your other questions. I have no experience with shaders. Sorry.

1 Like
3

Thank you;

I was able to modify the shader to accept the EXR as following, which removes a step:

shader_type spatial;
render_mode unshaded;
uniform sampler2DArray SHADOW_ATLAS : filter_nearest;
uniform vec4 lightmap_uv_rect;
void fragment() {
	ALBEDO = texture(SHADOW_ATLAS, vec3(UV2*lightmap_uv_rect.zw, 0)).rgb;
}

Inspecting the generated native code has not shed as much light on the issue as I would have hoped - I can see the sampler, but it is off-limits for gdshader code. Same goes for the UV[2] rect. And for the things that I can access, their gdshader name often doesn’t match with the name inside native code, which suggests that there’s a fixed set of identifiers that get mapped (likely the same as the auto-complete suggests) and that’s it.