bloom_threshold_shader.glsl

#version 330 core
uniform float threshold;
uniform float strength;
uniform sampler2D colorTexture;
in vec2 uv;
out vec4 fragColor;
void main()
{
    vec4 color = texture2D( colorTexture , uv );
    // convert rgb to grayscale/brightness
    float brightness = dot( color.rgb , vec3( 0.2126 , 0.7152 , 0.0722 ) );
    if ( brightness > threshold ) fragColor = vec4( strength * color.rgb , 1.0 );
    else fragColor = vec4( 0.0 , 0.0 , 0.0 , 1.0 );
}