fix: correct the formula for interpolating between bin start and end (interpolatedSignalRef)

examples/compiled/bar_month_band.vg.json

@@ -45,13 +45,13 @@
             "signal": "\"date (month): \" + (timeFormat(datum[\"month_date\"], timeUnitSpecifier([\"month\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"}))) + \"; Mean of precipitation: \" + (format(datum[\"mean_precipitation\"], \"\"))"
           },
           "x2": {
-            "signal": "scale(\"x\", 0.15000000000000002 * datum[\"month_date\"] + 0.85 * datum[\"month_date_end\"])",
+            "signal": "scale(\"x\", 0.85 * datum[\"month_date\"] + 0.15000000000000002 * datum[\"month_date_end\"])",
             "offset": {
               "signal": "0.5 + (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])) < 0.25 ? -0.5 * (0.25 - (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])))) : 0.5)"
             }
           },
           "x": {
-            "signal": "scale(\"x\", 0.85 * datum[\"month_date\"] + 0.15000000000000002 * datum[\"month_date_end\"])",
+            "signal": "scale(\"x\", 0.15000000000000002 * datum[\"month_date\"] + 0.85 * datum[\"month_date_end\"])",
             "offset": {
               "signal": "0.5 + (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])) < 0.25 ? 0.5 * (0.25 - (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])))) : -0.5)"
             }

examples/compiled/bar_month_band_config.vg.json

@@ -45,13 +45,13 @@
             "signal": "\"date (month): \" + (timeFormat(datum[\"month_date\"], timeUnitSpecifier([\"month\"], {\"year-month\":\"%b %Y \",\"year-month-date\":\"%b %d, %Y \"}))) + \"; Mean of precipitation: \" + (format(datum[\"mean_precipitation\"], \"\"))"
           },
           "x2": {
-            "signal": "scale(\"x\", 0.15000000000000002 * datum[\"month_date\"] + 0.85 * datum[\"month_date_end\"])",
+            "signal": "scale(\"x\", 0.85 * datum[\"month_date\"] + 0.15000000000000002 * datum[\"month_date_end\"])",
             "offset": {
               "signal": "0.5 + (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])) < 0.25 ? -0.5 * (0.25 - (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])))) : 0.5)"
             }
           },
           "x": {
-            "signal": "scale(\"x\", 0.85 * datum[\"month_date\"] + 0.15000000000000002 * datum[\"month_date_end\"])",
+            "signal": "scale(\"x\", 0.15000000000000002 * datum[\"month_date\"] + 0.85 * datum[\"month_date_end\"])",
             "offset": {
               "signal": "0.5 + (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])) < 0.25 ? 0.5 * (0.25 - (abs(scale(\"x\", datum[\"month_date_end\"]) - scale(\"x\", datum[\"month_date\"])))) : -0.5)"
             }

src/compile/data/timeunit.ts

@@ -32,12 +32,12 @@ function offsetAs(field: FieldName) {
 
 export class TimeUnitNode extends DataFlowNode {
   public clone() {
-    return new TimeUnitNode(null, duplicate(this.formula));
+    return new TimeUnitNode(null, duplicate(this.timeUnits));
   }
 
   constructor(
     parent: DataFlowNode,
-    private formula: Dict<TimeUnitComponent>
+    private timeUnits: Dict<TimeUnitComponent>
   ) {
     super(parent);
   }
@@ -101,13 +101,13 @@ export class TimeUnitNode extends DataFlowNode {
    * and removing `other`.
    */
   public merge(other: TimeUnitNode) {
-    this.formula = {...this.formula};
+    this.timeUnits = {...this.timeUnits};
 
     // if the same hash happen twice, merge
-    for (const key in other.formula) {
-      if (!this.formula[key]) {
+    for (const key in other.timeUnits) {
+      if (!this.timeUnits[key]) {
         // copy if it's not a duplicate
-        this.formula[key] = other.formula[key];
+        this.timeUnits[key] = other.timeUnits[key];
       }
     }
 
@@ -125,7 +125,7 @@ export class TimeUnitNode extends DataFlowNode {
   public removeFormulas(fields: Set<string>) {
     const newFormula = {};
 
-    for (const [key, timeUnitComponent] of entries(this.formula)) {
+    for (const [key, timeUnitComponent] of entries(this.timeUnits)) {
       const fieldAs = isTimeUnitTransformComponent(timeUnitComponent)
         ? timeUnitComponent.as
         : `${timeUnitComponent.field}_end`;
@@ -134,29 +134,29 @@ export class TimeUnitNode extends DataFlowNode {
       }
     }
 
-    this.formula = newFormula;
+    this.timeUnits = newFormula;
   }
 
   public producedFields() {
     return new Set(
-      vals(this.formula).map(f => {
+      vals(this.timeUnits).map(f => {
         return isTimeUnitTransformComponent(f) ? f.as : offsetAs(f.field);
       })
     );
   }
 
   public dependentFields() {
-    return new Set(vals(this.formula).map(f => f.field));
+    return new Set(vals(this.timeUnits).map(f => f.field));
   }
 
   public hash() {
-    return `TimeUnit ${hash(this.formula)}`;
+    return `TimeUnit ${hash(this.timeUnits)}`;
   }
 
   public assemble() {
     const transforms: (VgTimeUnitTransform | VgFormulaTransform)[] = [];
 
-    for (const f of vals(this.formula)) {
+    for (const f of vals(this.timeUnits)) {
       if (isTimeUnitTransformComponent(f)) {
         const {field, as, timeUnit} = f;
         const {unit, utc, ...params} = normalizeTimeUnit(timeUnit);

src/compile/mark/encode/position-rect.ts

@@ -242,7 +242,7 @@
   channel: PositionChannel | PolarPositionChannel,
   spacing: number,
   reverse: boolean | SignalRef,
-  translate: number | SignalRef,
+  axisTranslate: number | SignalRef,
   offset: number | VgValueRef,
   minBandSize: number | SignalRef,
   bandSizeExpr: string
@@ -255,10 +255,10 @@
 
   const spacingOffset = isEnd ? -spacing / 2 : spacing / 2;
 
-  if (isSignalRef(reverse) || isSignalRef(offset) || isSignalRef(translate) || minBandSize) {
+  if (isSignalRef(reverse) || isSignalRef(offset) || isSignalRef(axisTranslate) || minBandSize) {
     const reverseExpr = signalOrStringValue(reverse);
     const offsetExpr = signalOrStringValue(offset);
-    const translateExpr = signalOrStringValue(translate);
+    const axisTranslateExpr = signalOrStringValue(axisTranslate);
     const minBandSizeExpr = signalOrStringValue(minBandSize);
 
     const sign = isEnd ? '' : '-';
@@ -267,7 +267,7 @@
       ? `(${bandSizeExpr} < ${minBandSizeExpr} ? ${sign}0.5 * (${minBandSizeExpr} - (${bandSizeExpr})) : ${spacingOffset})`
       : spacingOffset;
 
-    const t = translateExpr ? `${translateExpr} + ` : '';
+    const t = axisTranslateExpr ? `${axisTranslateExpr} + ` : '';
     const r = reverseExpr ? `(${reverseExpr} ? -1 : 1) * ` : '';
     const o = offsetExpr ? `(${offsetExpr} + ${spacingAndSizeOffset})` : spacingAndSizeOffset;
 
@@ -276,7 +276,7 @@
     };
   } else {
     offset = offset || 0;
-    return translate + (reverse ? -offset - spacingOffset : +offset + spacingOffset);
+    return axisTranslate + (reverse ? -offset - spacingOffset : +offset + spacingOffset);
   }
 }
 
@@ -325,7 +325,7 @@
     bandSizeExpr
   );
 
-  const bandPosition = isSignalRef(bandSize)
+  const bandPositionForBandSize = isSignalRef(bandSize)
     ? {signal: `(1-${bandSize.signal})/2`}
     : isRelativeBandSize(bandSize)
     ? (1 - bandSize.band) / 2
@@ -336,13 +336,15 @@
       [vgChannel2]: rectBinRef({
         fieldDef,
         scaleName,
-        bandPosition,
+        bandPosition: bandPositionForBandSize,
         offset: binSpacingOffset2
       }),
       [vgChannel]: rectBinRef({
         fieldDef,
         scaleName,
-        bandPosition: isSignalRef(bandPosition) ? {signal: `1-${bandPosition.signal}`} : 1 - bandPosition,
+        bandPosition: isSignalRef(bandPositionForBandSize)
+          ? {signal: `1-${bandPositionForBandSize.signal}`}
+          : 1 - bandPositionForBandSize,
         offset: binSpacingOffset
       })
     };

src/compile/mark/encode/valueref.ts

@@ -191,8 +191,8 @@
     ref.field = field;
   } else {
     const datum = isSignalRef(bandPosition)
-      ? `${bandPosition.signal} * ${start} + (1-${bandPosition.signal}) * ${end}`
-      : `${bandPosition} * ${start} + ${1 - bandPosition} * ${end}`;
+      ? `(1-${bandPosition.signal}) * ${start} + ${bandPosition.signal} * ${end}`
+      : `${1 - bandPosition} * ${start} + ${bandPosition} * ${end}`;
     ref.signal = `scale("${scaleName}", ${datum})`;
   }
 

test/compile/mark/point.test.ts

@@ -121,7 +121,7 @@ describe('Mark: Point', () => {
     const props = point.encodeEntry(model);
 
     expect(props.x).toEqual({
-      signal: 'scale("x", 0.6 * datum["bin_maxbins_10_a"] + 0.4 * datum["bin_maxbins_10_a_end"])'
+      signal: 'scale("x", 0.4 * datum["bin_maxbins_10_a"] + 0.6 * datum["bin_maxbins_10_a_end"])'
     });
   });
   it('interpolates x timeUnit with timeUnitBand = 0.5', () => {