test.glsl

#VERTEX 

#version 300 es

precision mediump float;

in vec3 a_position;

void main()
{
    gl_Position = vec4(a_position, 1.0);
}

#FRAGMENT

#version 300 es    
precision mediump float;

struct LightInfo {
    vec3 position;
    vec3 inverse_direction;
    vec3 color_and_intensity;
    lowp int mode;
};

// NOTE: IF THIS UNIFORM IS REDUCED TO 'p_lights[10]' PERFORMANCE RETURNS TO 60 FPS
uniform LightInfo p_lights[100];

precision mediump float;

out vec4 color_out;

vec3 BRDF(LightInfo light) {
    vec3 l;
    float attenuation;

    // NOTE: IF THIS IS BRANCH IS REMOVED PERFORMANCE RETURNS TO 60 FPS
    if (light.mode == 0) {
        l = light.inverse_direction;
        attenuation = 1.0;
    } else {
        vec3 diff = light.position;
        float distance = length(diff);
        l = diff / distance;
        attenuation = 1.0 / (distance * distance);
    };

    // apply lighting...
    return l * light.color_and_intensity;
}

void main()
{
    color_out = vec4(0, 0, 0, 1);

    // NOTE: IF THIS IS BRANCH IS CHANGED TO 'i < 9' PERFORMANCE RETURNS TO 60 FPS
    for (int i = 0; i < 10; i++) {
        color_out.rgb += BRDF(p_lights[i]);
    }
}