pub const MAIN: &str = r#"
void main() {
vec2 uv = v_uv;
vec4 src = texture(tex, uv);
out_color = apply_mask(src, effect(src, uv), uv);
}
"#;Expand description
Entry point appended after a vec4 effect(vec4 src, vec2 uv) body: sample, run effect, mask.
Used by user_shader (EffectKind::Shader) and gpu.rs’s copy/matte programs only — the built-in
bodies below write out_color themselves.