halfplane.shadron

glsl {

    // Signed distance from half-plane defined by oriented line segment (a, b)
    float halfPlaneDistance(vec2 pos, vec2 a, vec2 b) {
        return dot(normalize(vec2(b.y-a.y, a.x-b.x)), a-pos);
    }

    // Anti-aliased half-plane defined by oriented line segment (a, b)
    float halfPlaneSmooth(vec2 pos, vec2 a, vec2 b, float border) {
        return clamp(halfPlaneDistance(pos, a, b)/border+0.5, 0.0, 1.0);
    }

}