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houdini vex: procedural tetrahedron roll about center point
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| float t = chf('time'); | |
| float seed = chf('seed'); | |
| int ti = int(6 * t) % 6; // integer time from 0-5 | |
| float tf = frac(6 * t); // fraction time | |
| // some random easing and motion reshaping: | |
| float start = lerp(0.0, 0.05, rand(seed + 5 * ti)); | |
| float stop = lerp(0.95, 1.0, rand(seed + 7 * ti)); | |
| float shape = lerp(0.5, 0.65, rand(seed + 11 * ti)); | |
| tf = fit(tf, start, stop, 0, 1); | |
| tf = pow(tf, shape); | |
| float dihedral = (PI - atan(2 * sqrt(2))); | |
| vector axis = {0, 0, 1}; | |
| matrix roty = ident(); | |
| rotate(roty, -PI / 3, {0, 1, 0}); | |
| vector pos = @P; | |
| vector up = {0, 1, 0}; | |
| vector N = {0, 0, 1}; | |
| for (int i = 0; i < 6; i++) { | |
| if (i > ti) break; | |
| float angle = (i == ti)? tf * -dihedral : -dihedral; | |
| matrix3 rot = ident(); | |
| rotate(rot, angle, axis); | |
| pos *= rot; | |
| up *= rot; | |
| N *= rot; | |
| axis *= roty; | |
| } | |
| v@up = up; | |
| v@N = N; | |
| v@P = pos; |
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