Stripped-down distance field rendering fragment shader

distance-field-shader.glsl

precision mediump float;

layout(location = 0) out vec4 fragColor;

uniform sampler2D u_glyphs;
uniform vec4 u_color;
uniform float u_aaStepScale;
uniform int u_aaSampling;

varying vec2 v_uv;

const int channel = 0;


float aastep(float t, float value)
{
    float afwidth = fwidth(value) * u_aaStepScale;

    return smoothstep(t - afwidth, t + afwidth, value);
}

float tex(float t, vec2 uv)
{
    return aastep(t, texture(u_glyphs, uv)[channel]);
}

void main(void)
{
    float a = tex(0.5, v_uv);

    if(a <= 0.0) {
        discard;
    }
    
    fragColor = vec4(u_color.rgb, u_color.a * a);
}