#version 330 core
in vec2 vUv;
in float vShade;
in float vWorldY;

out vec4 FragColor;

uniform sampler2D atlas;
uniform float u_caveDarkStartY;
uniform float u_caveDarkEndY;
uniform float u_caveMinBrightness;

void main()
{
    vec4 texel = texture(atlas, vUv);
    float t = clamp((u_caveDarkStartY - vWorldY) /
                    (u_caveDarkStartY - u_caveDarkEndY), 0.0, 1.0);
    float brightness = mix(1.0, u_caveMinBrightness, t);
    FragColor = vec4(texel.rgb * vShade * brightness, 1.0);
}