/** * 2-3 IK Rigger - Inverse Kinematics chain setup for Adobe After Effects * * Turns a set of existing layers into a working 2- or 3-segment IK chain. You * pick the limb segments, the limb tip, and a controller/goal layer; the script * parents the chain and writes a law-of-cosines IK rotation expression onto each * segment so the whole chain solves to follow the goal. A "Change IK Direction" * checkbox is added to the goal so you can flip the elbow/knee bend, and (in * 3-layer mode) a "Rotate Tip" checkbox controls whether the tip tracks the chain. * * FUNCTIONALITY: * - Builds a 2-layer (upper/lower/tip) or 3-layer (upper/middle/lower/tip) IK chain. * - Parents the segments into a chain and drives each segment's Rotation via a * closed-form IK expression (2-bone and 3-bone law-of-cosines solvers). * - Adds a "Change IK Direction" checkbox to the goal to flip the bend direction. * - Adds a "Rotate Tip" checkbox to the goal in 3-layer mode. * - Refresh re-reads the active comp's layers into every dropdown. * - Validates the active comp, the layer count, distinct picks, and locked layers * before it touches anything, inside a single undo group. * * USAGE: * 1. In your composition, create/position the layers you want as the chain: * - Upper segment, (Middle segment for 3-layer), Lower segment, a Limb Tip * layer at the very end of the chain (e.g. the hand/foot), and a Goal layer * (typically a Null) that you will animate to drive the chain. * 2. Set each segment layer's ANCHOR POINT on the joint it rotates around (the * upper anchor at the shoulder/hip, lower anchor at the elbow/knee, tip anchor * at the wrist/ankle). The IK math measures from these anchors. * 3. Run the script, choose "Two Layer IK Setup" or "Three Layer IK Setup", and * assign each dropdown to the matching layer (Set Limb Controller/Goal = the null). * 4. Click Apply. Animate the Goal null to pose the chain; toggle "Change IK * Direction" on the goal to flip the bend. * * REQUIREMENTS: * - An active composition with at least the required number of layers * (4 for 2-layer: upper, lower, tip, goal; 5 for 3-layer). * - Layers unlocked. Expression engine support for length(), clamp(), * radiansToDegrees(), toWorld(), and effect() references. * * NOTES: * - The catalog filename is 2-3_IK_Rigger.jsx; the toolbar slug is 2-3-ik-rigger. * - ExtendScript wrapper code is ECMA-3 compatible; the rig logic lives in AE * expressions applied to each segment's Rotation. * - Re-running Apply reuses the existing goal checkboxes instead of duplicating them. * * @name 2-3 IK Rigger * @author IVG Design * @version 1.0.0 * @date 2026-07-07 * @ui PALETTE * @license MIT * @changelog * 1.0.0 initial catalog release; fixed refresh, lock-check, undefined rotateHand * in the 3-layer expression, duplicate goal effect on re-apply, and added * active-comp/selection validation and a single guarded undo group. */ (function ik_rigger() { // ---- helpers ----------------------------------------------------------- function activeComp() { var item = app.project ? app.project.activeItem : null; return (item && item instanceof CompItem) ? item : null; } function layerNames(comp) { var names = []; for (var i = 1; i <= comp.numLayers; i++) names.push(comp.layer(i).name); return names; } function getLayerNamed(comp, name) { for (var i = 1; i <= comp.numLayers; i++) { if (comp.layer(i).name === name) return comp.layer(i); } return null; } function populateDD(dd, names) { var prev = dd.selection ? dd.selection.text : null; dd.removeAll(); for (var i = 0; i < names.length; i++) dd.add("item", names[i]); var restored = false; if (prev) { for (var j = 0; j < dd.items.length; j++) { if (dd.items[j].text === prev) { dd.selection = j; restored = true; break; } } } if (!restored && dd.items.length) dd.selection = 0; } // Reuse an existing Checkbox Control by name, or add a new one. function ensureCheckbox(layer, effectName, defaultOn) { var parade = layer.property("ADBE Effect Parade"); for (var i = 1; i <= parade.numProperties; i++) { if (parade.property(i).name === effectName) return parade.property(i); } var fx = parade.addProperty("ADBE Checkbox Control"); fx.name = effectName; if (defaultOn) fx.property("ADBE Checkbox Control-0001").setValue(1); return fx; } var comp = activeComp(); if (!comp) { alert("2-3 IK Rigger\nOpen a composition first."); return; } if (comp.numLayers < 4) { alert("2-3 IK Rigger\nNeed at least 4 layers (upper, lower, tip, goal)."); return; } var names = layerNames(comp); // ---- UI ----------------------------------------------------------------- var palette = new Window("palette", "IK Rig Setup", undefined, { resizeable: true }); palette.orientation = "column"; palette.alignChildren = ["left", "top"]; palette.spacing = 10; palette.margins = 16; var ik_type_selector = palette.add("panel", undefined, "Select IK Type"); ik_type_selector.orientation = "column"; ik_type_selector.alignChildren = ["left", "top"]; ik_type_selector.spacing = 10; ik_type_selector.margins = 14; var IK_Picker = ik_type_selector.add("group"); IK_Picker.orientation = "row"; IK_Picker.alignChildren = ["left", "center"]; IK_Picker.spacing = 10; var it1 = IK_Picker.add("statictext", undefined, "Inverse Kinematics Type"); it1.preferredSize.width = 160; var ik_type_picker = IK_Picker.add("dropdownlist", undefined, ["Two Layer IK Setup", "Three Layer IK Setup"]); ik_type_picker.selection = 0; ik_type_picker.preferredSize.width = 200; var layer_picker = palette.add("panel", undefined, "Pick Your Layers"); layer_picker.orientation = "column"; layer_picker.alignChildren = ["left", "top"]; layer_picker.spacing = 10; layer_picker.margins = 14; var hint = layer_picker.add("statictext", undefined, "Set each segment's anchor point on its joint. Assign the Limb Tip (chain end) and the Goal/Controller null.", { multiline: true }); hint.preferredSize.width = 360; function addRow(labelText) { var g = layer_picker.add("group"); g.orientation = "row"; g.alignChildren = ["left", "center"]; g.spacing = 10; var t = g.add("statictext", undefined, labelText); t.preferredSize.width = 160; var dd = g.add("dropdownlist", undefined, names); dd.selection = 0; dd.preferredSize.width = 200; g.dd = dd; return g; } var group1 = addRow("Set Upper Limb"); var group2 = addRow("Set Middle Limb"); group2.enabled = false; // 3-layer only var group3 = addRow("Set Lower Limb"); var group4 = addRow("Set Limb Tip"); var group5 = addRow("Set Limb Controller/Goal"); var upper_limb_selector = group1.dd; var middle_limb_selector = group2.dd; var lower_limb_selector = group3.dd; var limb_tip_selector = group4.dd; var goal_selector = group5.dd; var group6 = palette.add("group"); group6.orientation = "row"; group6.alignChildren = ["center", "top"]; group6.spacing = 10; var btn_refresh = group6.add("button", undefined, "Refresh"); btn_refresh.preferredSize.width = 75; var btn_apply = group6.add("button", undefined, "Apply"); btn_apply.preferredSize.width = 75; var btn_close = group6.add("button", undefined, "Close"); btn_close.preferredSize.width = 75; ik_type_picker.onChange = function () { group2.enabled = (this.selection.index === 1); }; btn_close.onClick = function () { palette.close(); }; btn_refresh.onClick = function () { var c = activeComp(); if (!c) { alert("2-3 IK Rigger\nOpen a composition first."); return; } names = layerNames(c); populateDD(upper_limb_selector, names); populateDD(middle_limb_selector, names); populateDD(lower_limb_selector, names); populateDD(limb_tip_selector, names); populateDD(goal_selector, names); }; // ---- IK expressions (law-of-cosines solvers; math preserved verbatim) --- function buildIK2(upper, lower, tip, goal) { return [ 'var upperLimb = thisComp.layer("' + upper.name + '");', 'var lowerLimb = thisComp.layer("' + lower.name + '");', 'var limbTip = thisComp.layer("' + tip.name + '");', 'var goal = thisComp.layer("' + goal.name + '");', 'var flip = thisComp.layer("' + goal.name + '").effect("Change IK Direction")("Checkbox");', 'function worldPos(a) { return a.toWorld(a.anchorPoint); }', 'function rotationFunction(from, x) {', ' var d = x - from;', ' return radiansToDegrees(Math.atan2(d[1], d[0]));', '}', 'var lTip = limbTip.index;', 'var uLimb = upperLimb.index;', 'var lLimb = lowerLimb.index;', 'var limbTipPosition = worldPos(limbTip);', 'var upperLimbPosition = worldPos(upperLimb);', 'var lowerLimbPosition = worldPos(lowerLimb);', 'var controllerPosition = worldPos(goal);', 'var upperToLowerDist = length(upperLimbPosition, lowerLimbPosition);', 'var lowerToTipDist = length(lowerLimbPosition, limbTipPosition);', 'var IKlength = length(controllerPosition, upperLimbPosition);', 'var LofC = (upperToLowerDist * upperToLowerDist - lowerToTipDist * lowerToTipDist + IKlength * IKlength) / (2 * IKlength);', 'var midPointIK = IKlength - LofC;', 'var angleB = Math.acos(clamp(midPointIK / lowerToTipDist, -1, 1));', 'var angleA = Math.acos(clamp(LofC / upperToLowerDist, -1, 1));', 'var lowerLimbRotationAngle = (flip == 1) ? (angleB + angleA) : -(angleB + angleA);', 'lowerLimbRotationAngle = radiansToDegrees(lowerLimbRotationAngle);', 'var uLimbAngleToIKline = (flip == 1) ? (-angleA) : (angleA);', 'uLimbAngleToIKline = radiansToDegrees(uLimbAngleToIKline);', 'var uLimbToIKLineAngle = rotationFunction(upperLimbPosition, controllerPosition);', 'var i = rotationFunction(upperLimbPosition, lowerLimbPosition);', 'var t = rotationFunction(lowerLimbPosition, limbTipPosition);', 'var output = value;', 'if (index == uLimb) {', ' output = uLimbAngleToIKline + uLimbToIKLineAngle - i + value;', '} else if (index == lLimb) {', ' output = lowerLimbRotationAngle + i - t + value;', '} else if (index == lTip) {', ' output = value - uLimbAngleToIKline - lowerLimbRotationAngle;', '}', 'output' ].join('\n'); } function buildIK3(upper, middle, lower, tip, goal) { return [ 'var upperLimb = thisComp.layer("' + upper.name + '");', 'var middleLimb = thisComp.layer("' + middle.name + '");', 'var lowerLimb = thisComp.layer("' + lower.name + '");', 'var limbTip = thisComp.layer("' + tip.name + '");', 'var goal = thisComp.layer("' + goal.name + '");', 'var flip = thisComp.layer("' + goal.name + '").effect("Change IK Direction")("Checkbox");', 'var rotateHand = thisComp.layer("' + goal.name + '").effect("Rotate Tip")("Checkbox");', 'function j(a) { return a.toWorld(a.anchorPoint); }', 'function i(a, d) { var c = d - a; return radiansToDegrees(Math.atan2(c[1], c[0])); }', 'var z = limbTip.index;', 'var p = upperLimb.index;', 'var h = middleLimb.index;', 'var k = lowerLimb.index;', 'var w = j(limbTip);', 'var v = j(upperLimb);', 'var u = j(middleLimb);', 'var t = j(lowerLimb);', 'var r = j(goal);', 'var O = length(v, u); if (O == 0) { O = 1; }', 'var N = length(u, t); if (N == 0) { N = 1; }', 'var J = length(t, w); if (J == 0) { J = 1; }', 'var H = length(v, r); if (H == 0) { H = 1; }', 'var y = N * N - H * H - (O - J) * (O - J);', 'var e = H * H * (O + J);', 'var o = -H * H * O * J;', 'var n = (-1 * e - Math.sqrt(e * e - 4 * y * o)) / (2 * y);', 'var I = Math.acos(clamp(H / (2 * n), -1, 1));', 'var f = (flip == 1) ? -I : I;', 'f = radiansToDegrees(f);', 'var l = Math.sqrt(H * H + J * J - 2 * H * J * Math.cos(I));', 'var g = Math.acos(clamp((l * l - O * O - N * N) / (-2 * O * N), -1, 1));', 'g = (flip == 1) ? radiansToDegrees(-g) : radiansToDegrees(g);', 'var F = Math.sqrt(H * H + O * O - 2 * H * O * Math.cos(I));', 'var x = Math.acos(clamp((F * F - J * J - N * N) / (-2 * J * N), -1, 1));', 'x = (flip == 1) ? radiansToDegrees(-x) : radiansToDegrees(x);', 'var K = i(v, r);', 'var m = i(v, u);', 'var C = i(u, t);', 'var s = i(t, w);', 'var q = value;', 'if (index == p) {', ' q = f + K - m + value;', '} else if (index == h) {', ' q = g + m - C + value + 180;', '} else if (index == k) {', ' q = x + C - s + value + 180;', '} else if (index == z && rotateHand == 1) {', ' q = value - f - g - x - K;', '}', 'q' ].join('\n'); } btn_apply.onClick = function () { var c = activeComp(); if (!c) { alert("2-3 IK Rigger\nOpen a composition first."); return; } var threeLayer = (ik_type_picker.selection.index === 1); // resolve + validate selections function pick(dd, role) { if (!dd.selection) { alert("2-3 IK Rigger\nChoose a layer for: " + role); return null; } var lyr = getLayerNamed(c, dd.selection.text); if (!lyr) { alert("2-3 IK Rigger\nLayer not found (Refresh): " + dd.selection.text); return null; } return lyr; } var upper = pick(upper_limb_selector, "Upper Limb"); if (!upper) return; var middle = threeLayer ? pick(middle_limb_selector, "Middle Limb") : null; if (threeLayer && !middle) return; var lower = pick(lower_limb_selector, "Lower Limb"); if (!lower) return; var tip = pick(limb_tip_selector, "Limb Tip"); if (!tip) return; var goal = pick(goal_selector, "Controller/Goal"); if (!goal) return; var chain = threeLayer ? [upper, middle, lower, tip, goal] : [upper, lower, tip, goal]; var seen = {}; for (var i = 0; i < chain.length; i++) { if (seen[chain[i].index]) { alert("2-3 IK Rigger\nEach role needs a distinct layer."); return; } seen[chain[i].index] = true; if (chain[i].locked) { alert("2-3 IK Rigger\nPlease unlock layer: " + chain[i].name); return; } } app.beginUndoGroup("2-3 IK Rig Setup"); try { ensureCheckbox(goal, "Change IK Direction", false); if (threeLayer) ensureCheckbox(goal, "Rotate Tip", true); if (!threeLayer) { var ik2 = buildIK2(upper, lower, tip, goal); lower.parent = upper; tip.parent = lower; upper.rotation.expression = ik2; lower.rotation.expression = ik2; tip.rotation.expression = ik2; alert("Two Layer IK Chain Rigged"); } else { var ik3 = buildIK3(upper, middle, lower, tip, goal); middle.parent = upper; lower.parent = middle; tip.parent = lower; upper.rotation.expression = ik3; middle.rotation.expression = ik3; lower.rotation.expression = ik3; tip.rotation.expression = ik3; alert("Three Layer IK Chain Rigged"); } } catch (err) { alert("2-3 IK Rigger\n" + err.toString()); } finally { app.endUndoGroup(); } palette.close(); }; palette.layout.layout(true); palette.show(); })();