ghostty glsl

modules/home/ghostty/degauss.glsl

@@ -0,0 +1,107 @@
+///degauss.glsl
+const float BOOT_DELAY = 0.45;
+
+// How hard the coil hits.
+const float WOBBLE_AMP    = 0.055;
+const float WAVE_FREQ     = 9.0;
+const float WAVE_SPEED    = 3.2;
+const float WAVE_GLIDE    = 0.35;
+const float WARBLE_HZ     = 7.0;
+const float WARBLE_DEPTH  = 0.25;
+const float CHROMA_AMP    = 0.016;
+const float FLASH_AMP     = 0.55;
+const float JITTER_AMP    = 0.006;
+const float SQUEEZE_AMP   = 0.075;
+const float BAND_SWEEPS   = 2.0;
+const bool  JUMP_DEGAUSS = false;
+const float CURSOR_JUMP  = 0.60;
+
+#define TAU 6.28318530718
+float envelope(float t) {
+    if (t <= 0.0 || t >= DURATION) return 0.0;
+    float k = t / DURATION;
+    float attack = 1.0 - exp(-45.0 * t);
+    float ring   = exp(-2.3 * k);
+    float tail   = 1.0 - k * k * k * k;
+    return attack * ring * tail;
+}
+float coilPhase(float t) {
+    float k = clamp(t / DURATION, 0.0, 1.0);
+    return WAVE_SPEED * t * (1.0 - 0.5 * WAVE_GLIDE * k);
+}
+
+float hash11(float x) {
+    return fract(sin(x * 78.233) * 43758.5453);
+}
+vec4 sampleTerm(vec2 uv) {
+    vec2 halfTexel = 0.5 / iResolution.xy;
+    return texture(iChannel0, clamp(uv, halfTexel, 1.0 - halfTexel));
+}
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    vec2 uv = fragCoord / iResolution.xy;
+
+    float amp = 0.0;
+    float t   = 0.0;
+
+    float boot = iTime - BOOT_DELAY;
+    float bootAmp = envelope(boot);
+    if (bootAmp > amp) { amp = bootAmp; t = boot; }
+
+    if (JUMP_DEGAUSS) {
+        float jump    = abs(iCurrentCursor.y - iPreviousCursor.y);
+        float elapsed = iTime - iTimeCursorChange;
+        if (jump > CURSOR_JUMP * iResolution.y) {
+            float e = envelope(elapsed);
+            if (e > amp) { amp = e; t = elapsed; }
+        }
+    }
+
+    if (amp <= 0.0001) {
+        fragColor = texture(iChannel0, uv);
+        return;
+    }
+
+    // coil's own tremble, so the picture pulses along with the warble in the
+    // sound instead of sliding smoothly under it.
+    amp *= 1.0 - WARBLE_DEPTH + WARBLE_DEPTH * sin(t * TAU * WARBLE_HZ);
+
+    float ph = coilPhase(t);
+
+    // magnetic distortion
+    vec2 p = uv - 0.5;
+
+    float wave  = sin(p.y * WAVE_FREQ * TAU - ph * TAU);
+    float wave2 = sin(p.y * WAVE_FREQ * 2.3 * TAU + ph * 0.62 * TAU);
+    float warp  = wave * 0.7 + wave2 * 0.3;
+
+    // vertical breathing
+    p.y /= 1.0 + amp * SQUEEZE_AMP * sin(t * TAU * 3.0);
+    p   *= 1.0 - amp * 0.04 * sin(t * TAU * 2.0);
+
+    // per-scanline jitter
+    float line   = floor(uv.y * iResolution.y);
+    float jitter = (hash11(line + floor(t * 90.0)) - 0.5) * 2.0;
+
+    p.x += amp * (WOBBLE_AMP * warp + JITTER_AMP * jitter);
+
+    vec2 duv = p + 0.5;
+
+    // misconvergence
+    float ca = amp * CHROMA_AMP * (0.5 + abs(warp));
+    vec4 cr = sampleTerm(duv + vec2(ca, 0.0));
+    vec4 cg = sampleTerm(duv);
+    vec4 cb = sampleTerm(duv - vec2(ca, 0.0));
+
+    vec4 col = vec4(cr.r, cg.g, cb.b, cg.a);
+
+    // coil pulse sweeping down the tube
+    float bandY = 1.0 - fract(t / DURATION * BAND_SWEEPS);
+    float band  = exp(-pow((uv.y - bandY) * 9.0, 2.0));
+
+    // background-opacity to solid for the length of the flash.
+    float glow = amp * FLASH_AMP * (0.25 + 0.75 * band);
+    col.rgb += glow * (iForegroundColor * 0.22 + col.rgb * 0.9);
+
+    fragColor = col;
+}