added trefoilKnotSdf

close #1285

Author: t3kt

docs/assets/images/reference/operators/sdf/trefoilKnotSdf_thumb.png

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+ReturnT thismap(CoordT p, ContextT ctx) {
+	CoordT p0 = p;
+	switch (THIS_Axis) {
+		case THISTYPE_Axis_x: p = p.zyx; break;
+		case THISTYPE_Axis_y: p = p.xzy; break;
+		case THISTYPE_Axis_z: p = p.yxz; break;
+	}
+
+	#ifdef THIS_EXPOSE_angle
+	THIS_angle = degrees(atan(p.y, p.x)) + 180.;
+	#endif
+	#ifdef THIS_EXPOSE_normangle
+	THIS_normangle = atan(p.y, p.x)/TAU + .5;
+	#endif
+
+	#ifdef THIS_HAS_INPUT_radiusField
+	float r = inputOp_radiusField(p0, ctx);
+	#else
+	float r = THIS_Radius;
+	#endif
+	#ifdef THIS_HAS_INPUT_thicknessField
+	float th = inputOp_thicknessField(p0, ctx);
+	#else
+	float th = THIS_Thickness;
+	#endif
+	return createSdf(sdTrefoilKnot(p, r, th));
+}

src/operators/sdf/index.tox

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+Trefoil knot SDF.
+
+Based on [Trefoil Knot Explained](https://www.shadertoy.com/view/M3tXW4) by ruudhelderman.
+
+## Parameters
+
+* `Axis`
+  * `x`
+  * `y`
+  * `z`
+* `Radius`
+* `Thickness`
+
+## Inputs
+
+* `radiusField`: 
+* `thicknessField`: 
+
+## Variables
+
+* `angle`: 
+* `normangle`: 

src/operators/sdf/trefoilKnotSdf.glsl

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+!rop
+meta: !meta
+  opType: raytk.operators.sdf.trefoilKnotSdf
+  opVersion: '0'
+  opStatus: beta
+opDef: !def
+  enable: true
+  typeSpec: !ropTypes
+    coordType: !coordT
+      Coordtypevec3: true
+    contextType: !contextT
+      Allcontexttype: true
+    returnType: !returnT
+      Returntypesdf: true
+  function: !text
+    file: src/operators/sdf/trefoilKnotSdf.glsl
+    name: function
+  paramGroupTable: eval_params
+  libraryNames: !expr
+    expr: op('trefoilKnotSdf_lib')
+  variableTable: !table
+    file: src/operators/sdf/trefoilKnotSdf_variables.txt
+    name: variable_exprs
+    evaluate: true
+    evalOpts: !evalOpts
+      excludeFirstRow: true
+      cols: enable
+  help: !text
+    file: src/operators/sdf/trefoilKnotSdf.md
+    name: help
+inputs:
+- !input
+  Localalias: radiusField
+  Variables: angle normangle
+  coordType: !coordT
+    Coordtypevec3: true
+  contextType: !contextT
+    Allcontexttype: true
+  returnType: !returnT
+    Returntypefloat: true
+- !input
+  Localalias: thicknessField
+  Variables: angle normangle
+  Variableinputs: radiusField
+  coordType: !coordT
+    Coordtypevec3: true
+  contextType: !contextT
+    Allcontexttype: true
+  returnType: !returnT
+    Returntypefloat: true

src/operators/sdf/trefoilKnotSdf.md

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+// https://www.shadertoy.com/view/M3tXW4
+// Trefoil Knot Explained by ruudhelderman
+
+// Parametric equation of the Trefoil Knot.
+// https://en.wikipedia.org/wiki/Trefoil_knot
+vec3 trf_pareq(in float t)
+{
+	return vec3(
+		sin(t) + 2.0 * sin(2.0 * t),
+		cos(t) - 2.0 * cos(2.0 * t),
+		-sin(3.0 * t)
+	);
+}
+
+// First derivative of the parametric equation.
+vec3 trf_pareq_derived(in float t)
+{
+	return vec3(
+		cos(t) + 4.0 * cos(2.0 * t),
+		-sin(t) + 4.0 * sin(2.0 * t),
+		-3.0 * cos(3.0 * t)
+	);
+}
+
+float trf_dist_origin_line(in vec3 p, in vec3 d)
+{
+	return length(cross(p, p + normalize(d)));
+}
+
+float trf_dist_point_curve(in vec3 p, in float s, in float t) {
+	return trf_dist_origin_line(p - s * trf_pareq(t), trf_pareq_derived(t));
+}
+
+float trf_rough_inverse(in vec3 p) {
+	return 0.5 * atan(p.x, -p.y);
+}
+
+float trf_improve_inverse(in vec3 p, in float s, in float t) {
+	vec3 d = trf_pareq_derived(t);
+	return -t - atan(-d.y, d.x);
+}
+
+// SDF for Trefoil Knot.
+// s = scale (size of the shape)
+// r = radius (thickness of the wire)
+float sdTrefoilKnot(in vec3 p, in float s, in float r)
+{
+    float t = trf_rough_inverse(p);
+
+    // There are 2 points on the curve that match t; calculate both.
+    float d1 = trf_dist_point_curve(p, s, trf_improve_inverse(p, s, t));
+    float d2 = trf_dist_point_curve(p, s, trf_improve_inverse(p, s, t + PI));
+
+    // Take whichever is closest to p.
+    return min(d1, d2) - r;
+}

src/operators/sdf/trefoilKnotSdf.tox

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+names	source	handling	readOnlyHandling	conversion	enable
+Radius	param	runtime	macro		op('radius_definition').numRows < 2
+Thickness	param	runtime	macro		op('thickness_definition').numRows < 2
+Axis	param	constant			1

src/operators/sdf/trefoilKnotSdf.yaml

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+name	label	dataType	enable	macros	category
+angle	Angle (0-360)	float	1
+normangle	Normalized Angle (0-1)	float	1