init

ghostty-shaders/spotlight.glsl

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+// Created by Paul Robello
+
+
+// Smooth oscillating function that varies over time
+float smoothOscillation(float t, float frequency, float phase) {
+    return sin(t * frequency + phase);
+}
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    // Resolution and UV coordinates
+	vec2 uv = fragCoord.xy / iResolution.xy;
+
+    // Used to fix distortion when calculating distance to circle center
+    vec2 ratio = vec2(iResolution.x / iResolution.y, 1.0);
+
+    // Get the texture from iChannel0
+    vec4 texColor = texture(iChannel0, uv);
+
+    // Spotlight center moving based on a smooth random pattern
+    float time = iTime * 1.0; // Control speed of motion
+    vec2 spotlightCenter = vec2(
+        0.5 + 0.4 * smoothOscillation(time, 1.0, 0.0),  // Smooth X motion
+        0.5 + 0.4 * smoothOscillation(time, 1.3, 3.14159) // Smooth Y motion with different frequency and phase
+    );
+
+    // Distance from the spotlight center
+    float distanceToCenter = distance(uv * ratio, spotlightCenter);
+
+    // Spotlight intensity based on distance
+    float spotlightRadius = 0.25; // Spotlight radius
+    float softness = 20.0;       // Spotlight edge softness. Higher values have sharper edge
+    float spotlightIntensity = smoothstep(spotlightRadius, spotlightRadius - (1.0 / softness), distanceToCenter);
+
+    // Ambient light level
+    float ambientLight = 0.5; // Controls the minimum brightness across the texture
+
+    // Combine the spotlight effect with the texture
+    vec3 spotlightEffect = texColor.rgb * mix(vec3(ambientLight), vec3(1.0), spotlightIntensity);
+
+    // Final color output
+    fragColor = vec4(spotlightEffect, texColor.a);
+}