From 27a4e2e426417184e86780857aff98603041890d Mon Sep 17 00:00:00 2001
From: April John <aprl@acab.dev>
Date: Fri, 16 Oct 2026 14:47:41 +0200
Subject: [PATCH] Add kik CRT terminal shader

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
---
 shaders/kik.glsl   | 56 ++++++++++++++++++++++++++++++++++++++++++++++
 shaders/pulse.glsl |  2 +-
 2 files changed, 57 insertions(+), 1 deletion(-)
 create mode 100644 shaders/kik.glsl

diff --git a/shaders/kik.glsl b/shaders/kik.glsl
new file mode 100644
index 0000000..1a35e1f
--- /dev/null
+++ b/shaders/kik.glsl
@@ -0,0 +1,56 @@
+// Khaos im Kiez: CRT terminal on the stairs (palette from berlin.ccc.de/kik)
+//
+// Output lines scroll along the stairs, the prompt sits on the last active
+// step with a blinking cursor, now and then a line is KiK red.
+
+const vec3 BG  = vec3(0.008, 0.040, 0.016);  // #020a04
+const vec3 FG  = vec3(0.200, 1.000, 0.400);  // #33ff66
+const vec3 DIM = vec3(0.122, 0.604, 0.247);  // #1f9a3f
+const vec3 HOT = vec3(1.000, 0.165, 0.165);  // #ff2a2a
+
+const float PROMPT_STEP = 12.0;  // last step trepped drives
+const float SCROLL_SPEED = 1.6;  // lines per second
+
+float hash(float n) {
+    return fract(sin(n * 12.9898) * 43758.5453);
+}
+
+// What line number n of the output looks like
+vec3 line(float n) {
+    float h = hash(n);
+    if (h < 0.15) return BG;                    // blank line
+    if (h > 0.92) return HOT * 0.9;             // "error"
+    float len = 0.25 + 0.75 * hash(n + 7.0);    // line length ~ brightness
+    return mix(DIM * 0.5, FG, len * len);
+}
+
+void mainImage(out vec4 fragColor, in vec2 fragCoord) {
+    float i = floor(fragCoord.x);
+    float s = iTime * SCROLL_SPEED;
+    float scroll = floor(s) + smoothstep(0.75, 1.0, fract(s));
+
+    vec3 col;
+    if (i < PROMPT_STEP - 1.0) {
+        // output area, lines move towards step 0
+        float n = i + scroll;
+        col = line(n);
+        // glow bleeding from neighbouring lines
+        col += 0.10 * (line(n - 1.0) + line(n + 1.0));
+    } else if (i < PROMPT_STEP) {
+        col = DIM * 0.9;                        // "visitor@khaos-im-kiez:~$"
+    } else if (i < PROMPT_STEP + 1.0) {
+        // cursor, blinks with steps(1) 1.1s like the site
+        col = fract(iTime / 1.1) < 0.5 ? FG : BG;
+    } else {
+        col = vec3(0.0);                        // not driven by trepped
+    }
+
+    // rolling scanline
+    float band = fract(i / 16.0 * 2.0 - iTime * 0.15);
+    col *= 1.0 - 0.35 * smoothstep(0.0, 0.1, band) * (1.0 - smoothstep(0.1, 0.25, band));
+
+    // slight CRT flicker
+    col *= 0.96 + 0.04 * hash(floor(iTime * 30.0));
+
+    fragColor = vec4(col, 1.0);
+}
diff --git a/shaders/pulse.glsl b/shaders/pulse.glsl
index 16cdcb3..22014df 100644
--- a/shaders/pulse.glsl
+++ b/shaders/pulse.glsl
@@ -1,7 +1,7 @@
 // Warm white pulse travelling along the stairs
 void mainImage(out vec4 fragColor, in vec2 fragCoord) {
     float x = fragCoord.x / iResolution.x;
-    float wave = 0.5 + 0.5 * sin(x * 6.2831 * 2.0 - iTime * 3.0);
+    float wave = 0.5 + 0.9 * sin(x * 12.2831 * 2.0 - iTime * 2);
     vec3 warm = vec3(1.0, 0.45, 0.1);
     fragColor = vec4(warm * wave, 1.0);
 }