Further improve normal corrector in spiro expansion

font-src/glyphs/letter/latin-ext/eszet.ptl

@@ -10,7 +10,6 @@ glyph-block Letter-Latin-Eszet : begin
 	glyph-block-import CommonShapes
 	glyph-block-import Common-Derivatives
 	glyph-block-import Letter-Shared-Shapes : FlatHookDepth
-	glyph-block-import Letter-Latin-S : SNeck
 
 	local ymiddle : [mix 0 CAP 0.5] - HalfStroke
 	local ymiddleCap : [mix 0 CAP 0.54] - HalfStroke

font-src/glyphs/letter/latin/s.ptl

@@ -23,13 +23,11 @@ glyph-block Letter-Latin-S : begin
 	define SLAB-INWARD    2
 
 	define SOBot  OX
-	define [SmallSTensionCoeff stroke] : mix [StrokeWidthBlend 1 0.375 stroke] 1 : clamp 0 1 : Math.pow (Width / (UPM * 0.55)) 0.5
-	define [SmallSDistCoeff] : Math.min 0.25 (0.1 * [Math.max 1 (Width / HalfUPM)])
 
-	glyph-block-export SNeck
+	define [SNeck] : params [[stroke Stroke]] : begin
-	define [SNeck] : params [[stroke Stroke] [slantCoeff 0] [tensionCoeff 1] [dist 0.1]] : begin
+		define tensionCoeff : mix [StrokeWidthBlend 1 0.375 stroke] 1 : clamp 0 1 : Math.pow (Width / (UPM * 0.55)) 0.5
-		define strokeCoeff : StrokeWidthBlend 0 1 stroke
+		define dist : Math.min 0.25 (0.1 * [Math.max 1 (Width / HalfUPM)])
-		define tension : tensionCoeff * (0.5 - 0.4 * dist - 0.005 * strokeCoeff + slantCoeff * TanSlope)
+		define tension : tensionCoeff * (0.5 - 0.4 * dist)
 		return : alsoThruThem {{(0.5 - dist) tension} {(0.5 + dist) (1 - tension)}} [widths.center stroke]
 
 	define [SStrokeDollarInterruptGap deltaX top bot gap stroke refSwEss] : begin
@@ -112,7 +110,7 @@ glyph-block Letter-Latin-S : begin
 						hookstart (XH - O) (sw -- stroke) (swItalicAdj -- Stroke)
 
 			g4   (SB - OX) (XH - smooth)
-			SNeck (stroke -- ess) (slantCoeff -- -0.02) (dist -- [SmallSDistCoeff]) (tensionCoeff -- [SmallSTensionCoeff stroke])
+			SNeck (stroke -- ess)
 			g4   (RightSB + OX - SOBot) (smooth) [widths 0 stroke]
 
 			match sb
@@ -155,7 +153,7 @@ glyph-block Letter-Latin-S : begin
 			g4   (RightSB + OX) (XH - SHook)
 			hookstart (XH - O) (sw -- stroke) (swItalicAdj -- Stroke)
 			g4   (SB - OX) (XH - smooth)
-			SNeck (stroke -- ess) (slantCoeff -- -0.02) (dist -- [SmallSDistCoeff]) (tensionCoeff -- [SmallSTensionCoeff stroke])
+			SNeck (stroke -- ess)
 			g4   (RightSB + OX - SOBot) (smooth) [widths 0 stroke]
 			arcvh
 			flat (Middle - CorrectionOMidS) 0 [widths 0 Stroke]
@@ -175,7 +173,7 @@ glyph-block Letter-Latin-S : begin
 					g4   (SB - OX) (XH - SHook) [widths.rhs stroke]
 					hookstart (XH - O) (sw -- stroke) (swItalicAdj -- Stroke)
 			g4   (RightSB + OX) (XH - smooth)
-			SNeck (stroke -- ess) (slantCoeff -- 0.02) (dist -- [SmallSDistCoeff]) (tensionCoeff -- [SmallSTensionCoeff stroke])
+			SNeck (stroke -- ess)
 			g4   (SB - OX + SOBot) (smooth) [widths stroke 0]
 			match sb
 				[Just SLAB-CLASSICAL] : SerifedArcEnd_LtrLhs RightSB Middle 0 stroke SHook

font-src/kits/spiro-kit.ptl

@@ -185,6 +185,11 @@ export : define [SetupBuilders args] : begin
 	define [convertSpiroToBezier knots closed ctx] : begin
 		return : SpiroJs.spiroToBezierOnContext knots closed ctx CurveUtil.SPIRO_PRECISION
 
+	define [iterateNormals s closed] : begin
+		local knotsP2 : s.getPass2Knots closed [fallback s.contrast Contrast]
+		local s2 : new SpiroExpansionContext2 s.controlKnots s.gizmo
+		SpiroJs.spiroToArcsOnContext knotsP2 closed s2
+
 	define [dispiro] : let [args : {}.slice.call arguments 0] : lambda [] : begin
 		define CLOSED true
 		local s : new SpiroExpansionContext1 (this.gizmo || GlobalTransform)
@@ -195,10 +200,8 @@ export : define [SetupBuilders args] : begin
 				if af : af.apply this args
 
 		SpiroJs.spiroToArcsOnContext knots closed s
-		local knotsP2 : s.getPass2Knots closed [fallback s.contrast Contrast]
+		iterateNormals s closed
-		# console.log knotsP2
+		iterateNormals s closed
-		local s2 : new SpiroExpansionContext2 s.controlKnots s.gizmo
-		SpiroJs.spiroToArcsOnContext knotsP2 closed s2
 		local {.lhs lhs .rhs rhs} : s.expand [fallback s.contrast Contrast]
 
 		if closed : then

font-src/meta/aesthetics.ptl

@@ -139,7 +139,7 @@ export : define [calculateMetrics para] : begin
 	define PeriodRadius : PeriodSize / 2
 	define SideJut : Jut - HalfStroke * HVContrast
 
-	define [StrokeWidthBlend min max sw] : linreg 18 min 126 max [fallback sw Stroke]
+	define [StrokeWidthBlend min max sw] : linreg para.canonicalStrokeWidthMin min para.canonicalStrokeWidthMax max [fallback sw Stroke]
 
 	define SmoothAdjust : StrokeWidthBlend 80 144
 	define [SmoothAOf smooth width] : smooth - TanSlope * SmoothAdjust / Width * width

font-src/support/parameters.js

@@ -87,8 +87,11 @@ function getBlendArg(blendArgs, style) {
 function hiveBlend(hive, value) {
 	if (!hive || !hive.blend || value == null) return hive;
 
-	const generatedHive = {};
 	const block = hive.blend;
+	delete hive.blend;
+
+	const generatedHive = { ...hive };
+
 	let keys = new Set();
 	for (const grade in block) {
 		if (!isFinite(parseFloat(grade))) continue;

font-src/support/spiro-expand.js

@@ -1,6 +1,17 @@
-const Transform = require("./transform");
 const { linreg } = require("./utils");
 
+class BiKnot {
+	constructor(type, x, y, d1, d2) {
+		this.type = type;
+		this.x = x;
+		this.y = y;
+		this.d1 = d1;
+		this.d2 = d2;
+		this.origTangent = null;
+		this.proposedNormal = null;
+	}
+}
+
 class SpiroExpansionContext1 {
 	constructor(gizmo) {
 		this.gizmo = gizmo;
@@ -13,30 +24,22 @@ class SpiroExpansionContext1 {
 	moveTo(x, y, unimportant) {
 		if (unimportant) return;
 		if (!isFinite(x) || !isFinite(y)) throw new Error("NaN detected.");
-		this.controlKnots.push({
+		const tfZ = this.gizmo.apply({ x, y });
-			type: "g4",
+		this.controlKnots.push(new BiKnot("g2", tfZ.x, tfZ.y, this.defaultD1, this.defaultD2));
-			d1: this.defaultD1,
-			d2: this.defaultD2,
-			...this.gizmo.apply({ x, y })
-		});
 	}
 	arcTo(arc, x, y) {
 		if (!isFinite(x) || !isFinite(y)) throw new Error("NaN detected.");
 		const k0 = this.controlKnots[this.controlKnots.length - 1];
 		if (!k0) throw new Error("Unreachable: lineTo called before moveTo");
-		if (k0.normalAngle == null) {
+		if (k0.origTangent == null) {
-			const tfDerive0 = this.gizmo.applyOffset({ x: arc.deriveX0, y: arc.deriveY0 });
+			k0.origTangent = this.gizmo.applyOffset({ x: arc.deriveX0, y: arc.deriveY0 });
-			k0.normalAngle = Math.PI / 2 + Math.atan2(tfDerive0.y, tfDerive0.x);
 		}
 		{
 			const tfDerive1 = this.gizmo.applyOffset({ x: arc.deriveX1, y: arc.deriveY1 });
-			this.controlKnots.push({
+			const tfZ = this.gizmo.apply({ x, y });
-				type: "g4",
+			const bz = new BiKnot("g2", tfZ.x, tfZ.y, k0.d1, k0.d2);
-				d1: k0.d1,
+			bz.origTangent = tfDerive1;
-				d2: k0.d2,
+			this.controlKnots.push(bz);
-				...this.gizmo.apply({ x, y }),
-				normalAngle: Math.PI / 2 + Math.atan2(tfDerive1.y, tfDerive1.x)
-			});
 		}
 	}
 	setWidth(l, r) {
@@ -87,8 +90,8 @@ class SpiroExpansionContext1 {
 				dx = knot.proposedNormal.x;
 				dy = knot.proposedNormal.y;
 			} else {
-				dx = normalX(knot.normalAngle, contrast);
+				dx = normalX(knot.origTangent, contrast);
-				dy = normalY(knot.normalAngle, contrast);
+				dy = normalY(knot.origTangent, contrast);
 			}
 			lhs[j] = {
 				type: knot.type,
@@ -155,24 +158,27 @@ class SpiroExpansionContext2 {
 	}
 	arcTo(arc, x, y) {
 		if (this.nKnotsProcessed === 1) {
-			const angle = computeNormalAngle(this.gizmo, arc.deriveX0, arc.deriveY0);
+			const d = this.gizmo.applyOffset({ x: arc.deriveX0, y: arc.deriveY0 });
-			if (isFinite(angle)) this.controlKnots[0].normalAngle = angle;
+			if (isTangentValid(d)) this.controlKnots[0].origTangent = d;
 			else throw new Error("NaN angle detected.");
 		}
 		{
-			const angle = computeNormalAngle(this.gizmo, arc.deriveX1, arc.deriveY1);
+			const d = this.gizmo.applyOffset({ x: arc.deriveX1, y: arc.deriveY1 });
-			if (isFinite(angle)) this.controlKnots[this.nKnotsProcessed].normalAngle = angle;
+			if (isTangentValid(d)) this.controlKnots[this.nKnotsProcessed].origTangent = d;
 			else throw new Error("NaN angle detected.");
 		}
 		this.nKnotsProcessed += 1;
 	}
 }
 
-function normalX(angle, contrast) {
+function isTangentValid(d) {
-	return Math.cos(angle) * contrast;
+	return isFinite(d.x) && isFinite(d.y);
 }
-function normalY(angle) {
+function normalX(tangent, contrast) {
-	return Math.sin(angle);
+	return contrast * (-tangent.y / Math.hypot(tangent.x, tangent.y));
+}
+function normalY(tangent) {
+	return tangent.x / Math.hypot(tangent.x, tangent.y);
 }
 function reverseKnotType(ty) {
 	return ty === "left" ? "right" : ty === "right" ? "left" : ty;

params/shape-weight.toml

@@ -1,3 +1,7 @@
+[shapeWeight]
+canonicalStrokeWidthMin = 18  # sync with 100 entry below
+canonicalStrokeWidthMax = 108 # sync with 900 entry below
+
 [shapeWeight.blend.400]
 stroke = 70        # Primary stroke width
 contrast = 1.11    # Stroke width contrast
@@ -89,3 +93,5 @@ vjut = 200
 smooth = 215
 rbalance = 50
 rbalance2 = 25
+cthin = 0.75
+cthinb = 0.5