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// Procedural star fragment shader
varying lowp vec2 vUV;
varying lowp float vSeed;
varying lowp float vScale;
const lowp float PI = 3.14159265359;
// Simple hash function for deterministic randomness
lowp float hash(lowp float n) {
return fract(sin(n) * 43758.5453123);
}
// Generate star pattern procedurally
lowp float starPattern(lowp vec2 uv) {
lowp float dist = length(uv);
lowp float angle = atan(uv.y, uv.x);
// Number of star points (4 or 5)
lowp float numPoints = 4.0 + floor(hash(vSeed) * 2.0);
// Create sharp star with triangular points
lowp float angleStep = 2.0 * PI / numPoints;
lowp float currentAngle = mod(angle + PI / numPoints, angleStep) - angleStep * 0.5;
// Create triangular points - distance from center to edge varies linearly with angle
lowp float normalizedAngle = abs(currentAngle) / (angleStep * 0.5);
// Outer tip radius and inner valley radius
lowp float tipRadius = 0.5;
lowp float valleyRadius = 0.15;
// Linear interpolation creates sharp triangular points
lowp float rayEdge = mix(tipRadius, valleyRadius, normalizedAngle);
// Hard cutoff for sharp edges
lowp float star = step(dist, rayEdge);
return star;
}
void main() {
lowp float pattern = starPattern(vUV);
// Color variation based on seed - white and blue tints
lowp float colorVar = hash(vSeed * 3.0);
lowp vec3 starColor;
if (colorVar < 0.5) {
// Pure white
starColor = vec3(1.0, 1.0, 1.0);
} else if (colorVar < 0.75) {
// Light blue tint
starColor = vec3(0.9, 0.95, 1.0);
} else {
// Stronger blue tint
starColor = vec3(0.85, 0.92, 1.0);
}
// Scale alpha based on size - smaller stars are more transparent
// Normalize scale from range [16, 48] to [0, 1]
lowp float sizeRatio = (vScale - 16.0) / (48.0 - 16.0);
// Map to alpha range [0.3, 1.0] - smaller stars at 30% opacity, larger at 100%
lowp float alpha = mix(0.3, 1.0, sizeRatio);
lowp vec4 color = vec4(starColor, pattern * alpha);
// Discard fully transparent pixels for performance
if (color.a < 0.01) {
discard;
}
gl_FragColor = color;
}
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