isleward/src/client/js/rendering/shaders/outline/frag.js

define([

], function (

) {
	return `
        varying vec2 vTextureCoord;
        uniform sampler2D uSampler;
        uniform vec4 filterClamp;

        uniform float uAlpha;
        uniform vec2 uThickness;
        uniform vec4 uColor;
        uniform bool uKnockout;

        const float DOUBLE_PI = 2. * 3.14159265358979323846264;
        const float ANGLE_STEP = $angleStep$;

        float outlineMaxAlphaAtPos(vec2 pos) {
            if (uThickness.x == 0. || uThickness.y == 0.) {
                return 0.;
            }

            vec4 displacedColor;
            vec2 displacedPos;
            float maxAlpha = 0.;

            for (float angle = 0.; angle <= DOUBLE_PI; angle += ANGLE_STEP) {
                displacedPos.x = vTextureCoord.x + uThickness.x * cos(angle);
                displacedPos.y = vTextureCoord.y + uThickness.y * sin(angle);
                displacedColor = texture2D(uSampler, clamp(displacedPos, filterClamp.xy, filterClamp.zw));
                maxAlpha = max(maxAlpha, displacedColor.a);
            }

            return maxAlpha;
        }

        void main(void) {
            vec4 sourceColor = texture2D(uSampler, vTextureCoord);
            vec4 contentColor = sourceColor * float(!uKnockout);
            float outlineAlpha = uAlpha * outlineMaxAlphaAtPos(vTextureCoord.xy) * (1.-sourceColor.a);
            vec4 outlineColor = vec4(vec3(uColor) * outlineAlpha, outlineAlpha);
            gl_FragColor = contentColor + outlineColor;
        }
    `;
});