75 lines
2.1 KiB
GLSL
75 lines
2.1 KiB
GLSL
#version 100
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precision mediump float;
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uniform float u_time;
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uniform vec2 u_resolution;
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// Constants
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#define PI 3.14159265359
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#define G 9.81
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#define L1 1.0
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#define L2 1.0
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#define M1 1.0
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#define M2 1.0
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#define DT 0.05
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#define ITERATIONS 100
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void main() {
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// Map pixel to initial angles (-PI to PI)
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vec2 uv = (gl_FragCoord.xy / u_resolution.xy) * 2.0 - 1.0;
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float t1 = uv.x * PI;
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float t2 = uv.y * PI;
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// Initial velocities
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float v1 = 0.0;
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float v2 = 0.0;
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// Previous angles for Verlet or just simple Euler/RK4
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// Using semi-implicit Euler for stability/simplicity in shader
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float flip_time = -1.0;
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// Animate gravity to make it breathe? Or length?
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float g = G + sin(u_time * 0.5) * 2.0;
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for (int i = 0; i < ITERATIONS; i++) {
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float num1 = -g * (2.0 * M1 + M2) * sin(t1);
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float num2 = -M2 * g * sin(t1 - 2.0 * t2);
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float num3 = -2.0 * sin(t1 - t2) * M2;
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float num4 = v2 * v2 * L2 + v1 * v1 * L1 * cos(t1 - t2);
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float den = L1 * (2.0 * M1 + M2 - M2 * cos(2.0 * t1 - 2.0 * t2));
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float a1 = (num1 + num2 + num3 * num4) / den;
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num1 = 2.0 * sin(t1 - t2);
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num2 = (v1 * v1 * L1 * (M1 + M2));
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num3 = g * (M1 + M2) * cos(t1);
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num4 = v2 * v2 * L2 * M2 * cos(t1 - t2);
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den = L2 * (2.0 * M1 + M2 - M2 * cos(2.0 * t1 - 2.0 * t2));
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float a2 = (num1 * (num2 + num3 + num4)) / den;
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v1 += a1 * DT;
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v2 += a2 * DT;
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t1 += v1 * DT;
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t2 += v2 * DT;
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// Dampening? No, chaotic system usually conservative (or we want to see chaos)
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// Check for flip (crossing PI)
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if (abs(t1) > PI || abs(t2) > PI) {
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flip_time = float(i) / float(ITERATIONS);
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break;
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}
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}
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vec3 col = vec3(0.0);
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if (flip_time > 0.0) {
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// Did flip
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col = vec3(0.2 + 0.8 * flip_time, 0.5 * flip_time, 1.0 - flip_time);
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} else {
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// Did not flip (stableish)
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col = vec3(0.1, 0.1, 0.2);
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}
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gl_FragColor = vec4(col, 1.0);
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}
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