src/render/shaders/glsl/rounding.glsl


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// smoothing constant for the edge: more = blurrier, but smoother
#define M_PI 3.1415926535897932384626433832795
#define SMOOTHING_CONSTANT (M_PI / 5.34665792551)

uniform float radius;
uniform float roundingPower;
uniform vec2 topLeft;
uniform vec2 fullSize;

vec4 rounding(vec4 color) {
    vec2 pixCoord = vec2(gl_FragCoord);
    pixCoord -= topLeft + fullSize * 0.5;
    pixCoord *= vec2(lessThan(pixCoord, vec2(0.0))) * -2.0 + 1.0;
    pixCoord -= fullSize * 0.5 - radius;
    pixCoord += vec2(1.0, 1.0) / fullSize; // center the pix don't make it top-left

    if (pixCoord.x + pixCoord.y > radius) {
        float dist = pow(pow(pixCoord.x, roundingPower) + pow(pixCoord.y, roundingPower), 1.0/roundingPower);

        if (dist > radius + SMOOTHING_CONSTANT)
            discard;

        float normalized = 1.0 - smoothstep(0.0, 1.0, (dist - radius + SMOOTHING_CONSTANT) / (SMOOTHING_CONSTANT * 2.0));

        color *= normalized;
    }

    return color;
}