Constant COMPOSITE_FRAG 

pub const COMPOSITE_FRAG: &str = r#"
#version 330 core

in  vec2 v_uv;
out vec4 frag_color;

uniform sampler2D u_scene;
uniform sampler2D u_bloom;
uniform float     u_intensity;

void main() {
    vec3 scene = texture(u_scene, v_uv).rgb;
    vec3 bloom = texture(u_bloom, v_uv).rgb;
    // Additive bloom blend
    vec3 result = scene + bloom * u_intensity;
    frag_color = vec4(result, 1.0);
}
"#;

GLSL fragment shader source for the bloom composite pass. Expects: u_scene: sampler2D — original scene u_bloom: sampler2D — blurred bloom u_intensity: float — additive blend weight u_dirt: sampler2D — optional lens dirt mask u_dirt_intensity: float