mirror of
https://github.com/3b1b/manim.git
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94 lines
2.6 KiB
GLSL
94 lines
2.6 KiB
GLSL
float cross2d(vec2 v, vec2 w){
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return v.x * w.y - w.x * v.y;
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}
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vec2 complex_div(vec2 v, vec2 w){
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return vec2(dot(v, w), cross2d(w, v)) / dot(w, w);
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}
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vec2 xs_on_clean_parabola(vec2 controls[3]){
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/*
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Given three control points for a quadratic bezier,
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this returns the two values (x0, x2) such that the
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section of the parabola y = x^2 between those values
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is isometric to the given quadratic bezier.
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Adapated from https://github.com/raphlinus/raphlinus.github.io/blob/master/_posts/2019-12-23-flatten-quadbez.md
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*/
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vec2 b0 = controls[0];
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vec2 b1 = controls[1];
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vec2 b2 = controls[2];
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vec2 dd = normalize(2 * b1 - b0 - b2);
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float u0 = dot(b1 - b0, dd);
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float u2 = dot(b2 - b1, dd);
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float cp = cross2d(b2 - b0, dd);
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return vec2(u0 / cp, u2 / cp);
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}
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mat3 map_point_pairs(vec2 src0, vec2 src1, vec2 dest0, vec2 dest1){
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/*
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Returns an orthogonal matrix which will map
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src0 onto dest0 and src1 onto dest1.
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*/
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mat3 shift1 = mat3(
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1.0, 0.0, 0.0,
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0.0, 1.0, 0.0,
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-src0.x, -src0.y, 1.0
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);
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mat3 shift2 = mat3(
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1.0, 0.0, 0.0,
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0.0, 1.0, 0.0,
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dest0.x, dest0.y, 1.0
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);
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// Compute complex division dest_vect / src_vect to determine rotation
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vec2 complex_rot = complex_div(dest1 - dest0, src1 - src0);
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mat3 rotate = mat3(
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complex_rot.x, complex_rot.y, 0.0,
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-complex_rot.y, complex_rot.x, 0.0,
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0.0, 0.0, 1.0
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);
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return shift2 * rotate * shift1;
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}
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mat3 get_xy_to_uv(vec2 controls[3], float temp_is_linear, out float is_linear){
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/*
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Returns a matrix for an affine transformation which maps a set of quadratic
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bezier controls points into a new coordinate system such that the bezier curve
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coincides with y = x^2, or in the case of a linear curve, it's mapped to the x-axis.
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*/
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vec2[2] dest;
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is_linear = temp_is_linear;
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// Portions of the parabola y = x^2 where x exceeds this value are just
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// treated as straight lines.
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float thresh = 2.0;
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if (!bool(is_linear)){
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vec2 xs = xs_on_clean_parabola(controls);
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float x0 = xs.x;
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float x2 = xs.y;
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if((x0 > thresh && x2 > thresh) || (x0 < -thresh && x2 < -thresh)){
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is_linear = 1.0;
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}else{
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dest[0] = vec2(x0, x0 * x0);
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dest[1] = vec2(x2, x2 * x2);
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}
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}
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// Check if is_linear status changed above
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if (bool(is_linear)){
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dest[0] = vec2(0, 0);
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dest[1] = vec2(1, 0);
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}
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return map_point_pairs(
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controls[0], controls[2], dest[0], dest[1]
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);
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}
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