Camera Post-Processing

Post-processing applies one or more fragment shaders to a camera's completed world image. Each camera owns an ordered effect stack, so split-screen and inset cameras can use different effects. Normal screen-space drawing, including Axolotl2D UI, is composited afterward and remains unchanged.

Create an effect

Inject the scene-scoped ShaderLibrary and a camera, then create effects in Load:

public sealed class GameplayScene(
    Camera2D camera,
    ShaderLibrary shaders) : BaseScene
{
    private PostProcessEffect vignette = null!;

    public override void Load() =>
        vignette = shaders.CreatePostProcess(camera, VignetteFragmentShader);
}

The library supplies the full-screen vertex shader. Your fragment shader receives normalized texture coordinates and can use these engine-provided uniforms when declared:

sampler2D uTexture: the previous pass, or the camera image for the first pass
vec2 uResolution: camera render-target size in pixels
vec2 uTexelSize: reciprocal render-target size, useful for neighboring pixel samples

#version 330 core
uniform sampler2D uTexture;
in vec2 frag_texCoords;
out vec4 out_color;

void main()
{
    vec4 color = texture(uTexture, frag_texCoords);
    float distanceFromCenter = length(frag_texCoords - 0.5);
    float amount = 1.0 - smoothstep(0.25, 0.7, distanceFromCenter) * 0.65;
    out_color = vec4(color.rgb * amount, color.a);
}

Render targets follow the camera viewport size and are recreated automatically after a window or viewport resize.

Set Camera2D.RenderTarget to send the final effect output to a public render texture instead of the window. In that case, effect uniforms use the render texture dimensions. See Render Textures.

Stack effects

Effects run in creation order:

var distortion = shaders.CreatePostProcess(camera, DistortionShader);
var grayscale = shaders.CreatePostProcess(camera, GrayscaleShader);
var vignette = shaders.CreatePostProcess(camera, VignetteShader);

Every pass samples the output of the previous pass. Set custom uniforms through effect.Shader, and toggle a pass without rebuilding the stack:

distortion.Shader.SetFloat("uTime", elapsedTime);
grayscale.Enabled = false;

PostProcessEffect.Dispose detaches one effect. Normally no manual cleanup is needed: the scene's ShaderLibrary detaches its effects and disposes their programs when the scene scope ends.

Post-processing is intentionally shader-based rather than a material system. A pass is one program plus its uniforms; create separate programs when two cameras need different persistent uniform values.

See the POST FX screen in Axolotl2D.Example for animated distortion, grayscale, vignette, pixelation, chromatic aberration, ordering, and runtime toggles. It also combines the stack with Camera2D.Shake to demonstrate a non-shader camera effect.

Table of Contents

Camera Post-Processing

Create an effect

Stack effects