fix: more flexible drawValues and value formatter

Author: farfromrefug

src/charting/formatter/IValueFormatter.ts

@@ -14,6 +14,8 @@ export interface IValueFormatter {
    *
    * @param value           the value to be formatted
    * @param entry           the entry the value belongs to - in e.g. BarChart, this is of class BarEntry
+   * @param index    index of the drawn value
+   * @param count    total number of values drawn (useful to draw first or last)
    * @param dataSetIndex    the index of the DataSet the entry in focus belongs to
    * @param viewPortHandler provides information about the current chart state (scale, translation, ...)
    * @return the formatted label ready for being drawn
@@ -23,6 +25,8 @@ export interface IValueFormatter {
   getFormattedValue(
     value: number,
     entry: Entry,
+    index,
+    count,
     dataSetIndex,
     viewPortHandler
   ): string;

src/charting/renderer/LineChartRenderer.ts

@@ -510,7 +510,7 @@ export class LineChartRenderer extends LineRadarRenderer {
     private mLineBuffer: number[];
 
     @profile
-    public drawValuesForDataset(c: Canvas, dataSet: LineDataSet) {
+    public drawValuesForDataset(c: Canvas, dataSet: LineDataSet, dataSetIndex: number) {
         const yKey = dataSet.yProperty;
         // apply the text-styling defined by the DataSet
         this.applyValueTextStyle(dataSet);
@@ -524,26 +524,36 @@ export class LineChartRenderer extends LineRadarRenderer {
 
         this.mXBounds.set(this.mChart, dataSet, this.mAnimator);
 
-        const positions = trans.generateTransformedValues(dataSet, this.mAnimator.getPhaseX(), this.mAnimator.getPhaseY(), this.mXBounds.min, this.mXBounds.max);
+        const { points, count } = trans.generateTransformedValues(dataSet, this.mAnimator.getPhaseX(), this.mAnimator.getPhaseY(), this.mXBounds.min, this.mXBounds.max);
         const formatter = dataSet.getValueFormatter();
 
         const iconsOffset = dataSet.getIconsOffset();
         const valuesOffset = dataSet.getValuesOffset();
         const drawIcons = dataSet.isDrawIconsEnabled();
         const drawValues = dataSet.isDrawValuesEnabled();
-        for (let j = 0; j < positions.length; j += 2) {
-            let x = positions[j];
-            let y = positions[j + 1];
+        const length = count;
+        const dataSetCount = dataSet.getEntryCount();
+        for (let j = 0; j < length; j += 2) {
+            let x = points[j];
+            let y = points[j + 1];
 
             if (!this.mViewPortHandler.isInBoundsRight(x)) break;
 
             if (!this.mViewPortHandler.isInBoundsLeft(x) || !this.mViewPortHandler.isInBoundsY(y)) continue;
 
-            let entry = dataSet.getEntryForIndex(j / 2 + this.mXBounds.min);
+            const index = j / 2 + this.mXBounds.min;
+            let entry = dataSet.getEntryForIndex(index);
             if (!entry) continue;
 
             if (drawValues) {
-                this.drawValue(c, formatter.getFormattedValue(entry[yKey]), valuesOffset.x + x, valuesOffset.y + y - valOffset, dataSet.getValueTextColor(j / 2));
+                // console.log('drawValue', entry[yKey], entry, index, dataSetCount);
+                this.drawValue(
+                    c,
+                    formatter.getFormattedValue(entry[yKey], entry, index, dataSetCount, dataSetIndex, this.mViewPortHandler),
+                    valuesOffset.x + x,
+                    valuesOffset.y + y - valOffset,
+                    dataSet.getValueTextColor(j / 2)
+                );
             }
 
             if (drawIcons && entry.icon != null) {

src/charting/utils/Transformer.ts

@@ -121,7 +121,7 @@ export class Transformer {
     // let count = (to - from + 1) * 2; //  Math.ceil((to - from) * phaseX) * 2;
 
         if (!this.valuePointsForGenerateTransformedValues || this.valuePointsForGenerateTransformedValues.length <  count) {
-            this.valuePointsForGenerateTransformedValues = Utils.createArrayBuffer(count);;
+            this.valuePointsForGenerateTransformedValues = Utils.createArrayBuffer(count);
         }
         // let valuePoints = this.valuePointsForGenerateTransformedValues;
         const valuePoints = this.valuePointsForGenerateTransformedValues;
@@ -143,7 +143,7 @@ export class Transformer {
 
         this.getValueToPixelMatrix().mapPoints(points);
 
-        return points;
+        return {points, count};
     }
 
     // protected valuePointsForGenerateTransformedValuesLine = [];