From 2e0840d7ede79468a8e639059e72d8337ed5ffd5 Mon Sep 17 00:00:00 2001
From: Leo Tenenbaum <pommicket@gmail.com>
Date: Thu, 1 Apr 2021 12:58:31 -0400
Subject: another shader

---
 03f.glsl | 84 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 03v.glsl |  9 +++++++
 main.c   |  3 +++
 3 files changed, 96 insertions(+)
 create mode 100644 03f.glsl
 create mode 100644 03v.glsl

diff --git a/03f.glsl b/03f.glsl
new file mode 100644
index 0000000..187ddd0
--- /dev/null
+++ b/03f.glsl
@@ -0,0 +1,84 @@
+varying vec2 pos;
+uniform float u_aspect_ratio;
+uniform float u_time;
+
+
+#define PI 3.14159265
+#define TAU 6.28318530718
+
+float rand(vec2 co) {
+    return fract(sin(dot(co, vec2(12.9898,78.233))) * 43758.5453);
+}
+
+// see https://en.wikipedia.org/wiki/HSL_and_HSV#HSV_to_RGB_alternative
+float hsvf(float n, vec3 hsv) {
+	float k = mod(n + hsv.x * 6.0, 6.0);
+	return hsv.z - hsv.z * hsv.y * clamp(min(k, 4.0 - k), 0.0, 1.0);
+}
+
+vec3 hsv_to_rgb(vec3 hsv) {
+	return vec3(hsvf(5.0, hsv), hsvf(3.0, hsv), hsvf(1.0, hsv));
+}
+
+
+// see https://en.wikipedia.org/wiki/Error_function#Inverse_functions
+float inv_erf(float z) {
+	return 0.5 * sqrt(PI) * z *
+		(1.0 + z * z *
+		(0.2617993878 + z * z *
+		(0.1439317308 + z * z *
+		(0.0976636195 + z * z *
+		(0.0732990794 + z * z *
+		(0.0583725009))))));
+}
+
+float distance2(vec2 a, vec2 b) {
+	return dot(a-b, a-b);
+}
+
+// inverse of the normal cumulative density function
+// see https://en.wikipedia.org/wiki/Normal_distribution#Quantile_function
+float inv_norm(float p, float mu, float sigma) {
+	return mu + sigma * sqrt(2.0) * inv_erf(2.0 * p - 1.0);
+}
+
+void main() {
+	vec3 p = vec3(pos, u_time);
+	p.x *= u_aspect_ratio;
+	float z = p.z;
+	
+	float t = 0.0;
+	for (float i = 0.0; i < 10.0; i += 1.0) {
+		float r = rand(vec2(i + 1.0, i + 1.0));
+		vec2 loc = vec2(
+			sin(1.0 * z * r),
+			tan(1.0 * z * r)
+		);
+		loc *= 0.5;
+		loc += 0.5;
+		loc.x *= u_aspect_ratio;
+	
+		float term = 1.0 - distance(p.xy, loc);
+		term = clamp(term, 0.0, 1.0);
+		t = max(t, term);
+	}
+	
+	
+	float n = 2.0 + 2.0 * (0.5 + 0.5 * sin(z));
+	t = fract(t*n);
+	t *= pow(sin(t * 40.0), 6.0 * pow(0.5 + 0.5 * sin(z), 3.0));
+	
+	float v = t < 0.5 ? 0.0 : 1.0;
+	
+	
+	float h = max(t - 0.5, 0.0) * 2.0;
+	
+	
+	h *= 0.2;
+	h += 0.7;
+	
+	float s = 1.0;
+	vec3 hsv = vec3(h, s, v);
+	gl_FragColor = vec4(hsv_to_rgb(hsv), 1.0);
+	
+}
diff --git a/03v.glsl b/03v.glsl
new file mode 100644
index 0000000..d5286df
--- /dev/null
+++ b/03v.glsl
@@ -0,0 +1,9 @@
+attribute vec2 v_render_pos;
+attribute vec2 v_pos;
+
+varying vec2 pos;
+
+void main() {
+	gl_Position = vec4(v_render_pos, 0.0, 1.0);
+	pos = v_pos;
+}
diff --git a/main.c b/main.c
index 8ba68c8..829f45a 100644
--- a/main.c
+++ b/main.c
@@ -271,6 +271,9 @@ int main(void) {
 					else
 						viewing_shader = -1;
 					break;
+				case SDLK_r:
+					start_time = time_get_seconds();
+					break;
 				case SDLK_F11:
 					fullscreen = !fullscreen;
 					SDL_SetWindowFullscreen(window, fullscreen ? SDL_WINDOW_FULLSCREEN_DESKTOP : 0);
-- 
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