Titan angled waist (#3493)

This allows tilting the waist on Titan. Closes #1102 

Code by @anna-puk

designs/paco/src/back.mjs

@@ -76,7 +76,7 @@ function pacoBack({
   // Adapt waist so we can get these pants over our bum without a zipper
   let delta =
     (measurements.seat * options.legBalance) / 2 - points.styleWaistIn.dist(points.styleWaistOut)
-  let angle = points.styleWaistIn.angle(points.styleWaistOut)
+  let angle = points.styleWaistInNoAngle.angle(points.styleWaistOut)
   points.styleWaistOut = points.styleWaistOut.shift(angle, delta)
   points.seatOut = points.seatOut.shift(angle, delta)
 

designs/paco/src/front.mjs

@@ -88,7 +88,7 @@ function pacoFront({
   let delta =
     (measurements.seat * (1 - options.legBalance)) / 2 -
     points.styleWaistIn.dist(points.styleWaistOut)
-  let angle = points.styleWaistIn.angle(points.styleWaistOut)
+  let angle = points.styleWaistInNoAngle.angle(points.styleWaistOut)
   points.styleWaistOut = points.styleWaistOut.shift(angle, delta)
   points.seatOut = points.seatOut.shift(angle, delta)
 

designs/titan/src/back.mjs

@@ -17,6 +17,7 @@ function titanBack({
   sa,
   absoluteOptions,
   log,
+  units,
   part,
 }) {
   /*
@@ -237,6 +238,25 @@ function titanBack({
     points.styleWaistIn = points.waistIn.clone()
     points.styleWaistOut = points.waistOut.clone()
   }
+  // Now angle the waist (if requested)
+  // create a backup of the unangled position, for use in dependent patterns
+  points.styleWaistInNoAngle = points.styleWaistIn.clone()  
+  if (options.waistAngle != 0 && (options.useWaistAngleFor === 'both' || options.useWaistAngleFor === 'backOnly') ) {
+    // calculate how much to add/subtract
+    // assume that from the crossSeamCurveStart upwards, the crotch seam will be vertical
+    // base of the triangle is then horizontal distance from crossSeamCurveStart to fork
+    let triangleBase, triangleHeight
+    // use positive value for triangleBase: positive angle means higher back 
+    triangleBase = points.fork.dx(points.crossSeamCurveStart)
+    // length of opposite side is length of adjacent side times tangent of the angle
+    triangleHeight = Math.tan(options.waistAngle * Math.PI/180) * triangleBase
+       
+    // top of cross seam is a straight line, so just extend
+    points.styleWaistIn = points.crossSeamCurveStart.shiftOutwards(points.styleWaistIn,triangleHeight)
+    
+    // report the change in height
+    log.info(['additionalHeightCenterBack',units(triangleHeight)])
+  }
   // Adapt the vertical placement of the seat control point to the lowered waist
   points.seatOutCp2.y = points.seatOut.y - points.styleWaistOut.dy(points.seatOut) / 2
 
@@ -425,6 +445,17 @@ export const back = {
     lengthBonus: { pct: 2, min: -20, max: 10, menu: 'style' },
     crotchDrop: { pct: 2, min: 0, max: 15, menu: 'style' },
     fitKnee: { bool: false, menu: 'style' },
+    waistAngle: { deg: 0, min: -20, max: 20, menu: 'style' },
+    useWaistAngleFor: {
+      dflt: "both",
+      list: [
+        "both",
+        "backOnly",
+        "frontOnly",
+      ],
+      menu: 'style'
+    },
+
     // Advanced
     legBalance: { pct: 57.5, min: 52.5, max: 62.5, menu: 'advanced' },
     crossSeamCurveStart: { pct: 85, min: 60, max: 100, menu: 'advanced' },

designs/titan/src/front.mjs

@@ -16,6 +16,7 @@ function titanFront({
   sa,
   absoluteOptions,
   log,
+  units,
   part,
 }) {
   /*
@@ -315,6 +316,25 @@ function titanFront({
     points.styleWaistIn = points.waistIn.clone()
     points.styleWaistOut = points.waistOut.clone()
   }
+  // Now angle the waist (if requested)
+  // create a backup of the unangled position, for use in dependent patterns
+  points.styleWaistInNoAngle = points.styleWaistIn.clone()  
+  if (options.waistAngle != 0 && (options.useWaistAngleFor === 'both' || options.useWaistAngleFor === 'frontOnly') ) {
+    // calculate how much to add/subtract
+    // assume that from the crossSeamCurveStart upwards, the crotch seam will be vertical
+    // base of the triangle is then horizontal distance from crossSeamCurveStart to fork
+    let triangleBase, triangleHeight
+    // use negative value for triangleBase: positive angle means lower front
+    triangleBase = points.fork.dx(points.crotchSeamCurveStart)
+    // length of opposite side is length of adjacent side times tangent of the angle
+    triangleHeight = Math.tan(options.waistAngle * Math.PI/180) * triangleBase
+    
+    // top of cross seam is a straight line, so just extend
+    points.styleWaistIn = points.crotchSeamCurveStart.shiftOutwards(points.styleWaistIn,triangleHeight)
+    
+    // report the change in height
+    log.info(['heightReductionCenterFront',units(-triangleHeight)])    
+  }
 
   // Seamline
   paths.seam = drawPath().attr('class', 'fabric')