CompositorEffect postprocessing with mipmapped screen texture

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1

Godot Version

4.6.3

Question

I try to create a simple “blur” post processing compositor, using mipmaps but I don’t know how to pass in a sampler that contains the mipmaps. I basically do:

var sampler_state := RDSamplerState.new()
sampler_state.min_filter = RenderingDevice.SAMPLER_FILTER_LINEAR
sampler_state.mag_filter = RenderingDevice.SAMPLER_FILTER_LINEAR
sampler_state.mip_filter = RenderingDevice.SAMPLER_FILTER_LINEAR
linear_sampler = rd.sampler_create(sampler_state)
.
.
var input_image: RID = render_scene_buffers.get_color_layer(0)
.
.
var uniform_sampler := RDUniform.new()
uniform_sampler.uniform_type = RenderingDevice.UNIFORM_TYPE_SAMPLER_WITH_TEXTURE
uniform_sampler.binding = 0
uniform_sampler.add_id(linear_sampler)
uniform_sampler.add_id(input_image)

and in the shader:

layout (set = 0, binding = 0) uniform sampler2D color_texture;
.
.
vec3 vScreenCol = textureLod(color_texture, uv, fScreenBlur).rgb;

I also tried to use render_scene_buffers.get_color_texture(), but this doesn’t make a difference.

btw: using a simple canvaslayer with color rect works perfect (eg: https://bun3d.com/tutorials/misc/godot_blur_shader/#full-shader) but I thought having it as compositor gives more flexbility.

2

The engine won’t create a copy of the screen texture with mipmaps unless necessary. The Environment glow effect creates it for example.

You can get the screen texture with mipmaps with RenderSceneBuffersRD.get_texture() like render_scene_buffers.get_texture("render_buffers", "blur_0")

I’ve not tested it but I’m pretty sure that this will only work in the post-transparent pass.

3

no, it doesn’t seem to work. interestingly, the first time

render_scene_buffers.get_texture(&"render_buffers", &"blur_0") is called, it gives and error:

  ERROR: servers/rendering/renderer_rd/storage_rd/render_scene_buffers_rd.cpp:390 - Condition "!named_textures.has(key)" is true. Returning: RID()

but the 2nd time, it returns a black/empty texture. and I think from then on it’s kind of cached?

4

Right, my bad. Looks like glow happens after applying the compositor effects so the texture is invalid.

In that case the only option I can think of is using the screen texture in a material so the engine copies the screen before the compositor effects are applied.

Something like:

shader_type spatial;

uniform sampler2D screen_texture: hint_screen_texture, filter_linear_mipmap;

void fragment() {
	vec4 color = texture(screen_texture, SCREEN_UV);
}

Applied to mesh should be enough to trigger it.

I did it with a quad mesh of size 0,0

5

thanks. that works, as long as the quad is visible; so I added it as a child of the camera.

6

I just realized that it “copies” the screen before the transparent objects are rendered, even if the post process uses POST_TRANSPARENT. It also doesn’t help if I set the instance to transparent or modify the alpha channel.

7

Yes, hint_screen_texture runs before the transparent pass.

You could do the blur yourself or open a proposal in the proposals repo if you find it necessary.