How to set both axis's scales to be always the same? - mpandroidchart

Question

MPAndroidChart allows you to zoom in the X axis, Y axis and both. I would like to rescale the remaining axis (or both) to match the one(s) being scaled.
For that I've created a OnChartGestureListener:
public class ZoomNotDistorting implements OnChartGestureListener {
private Chart chart;
private ViewPortHandler viewPortHandler;
private float startDist = 1f;
private float scaleX, scaleY;
public ZoomNotDistorting(Chart chart) {
this.chart = chart;
this.viewPortHandler = chart.getViewPortHandler();
}
#Override
public void onChartGestureStart(MotionEvent me, ChartTouchListener.ChartGesture lastPerformedGesture) {
int action = me.getAction() & MotionEvent.ACTION_MASK;
if(action == MotionEvent.ACTION_POINTER_DOWN && me.getPointerCount() >= 2) {
startDist = spacing(me);
}
}
#Override
public void onChartGestureEnd(MotionEvent me, ChartTouchListener.ChartGesture lastPerformedGesture) {
switch (lastPerformedGesture) {
case PINCH_ZOOM:
float scale = spacing(me) / startDist; // total scale
boolean isZoomingOut = (scale < 1);
if(isZoomingOut) {
if(scaleX < scaleY) {
viewPortHandler.zoom(scaleX, scaleX);
} else {
viewPortHandler.zoom(scaleY, scaleY);
}
} else {
if(scaleX > scaleY) {
viewPortHandler.zoom(scaleX, scaleX);
} else {
viewPortHandler.zoom(scaleY, scaleY);
}
}
break;
case X_ZOOM:
viewPortHandler.zoom(scaleX, scaleX);
break;
case Y_ZOOM:
viewPortHandler.zoom(scaleY, scaleY);
break;
}
chart.invalidate();
}
#Override
public void onChartLongPressed(MotionEvent me) {}
#Override
public void onChartDoubleTapped(MotionEvent me) {}
#Override
public void onChartSingleTapped(MotionEvent me) {}
#Override
public void onChartFling(MotionEvent me1, MotionEvent me2, float velocityX, float velocityY) {}
#Override
public void onChartScale(MotionEvent me, float scaleX, float scaleY) {
this.scaleX = scaleX;
this.scaleY = scaleY;
}
#Override
public void onChartTranslate(MotionEvent me, float dX, float dY) {}
/**
* returns the distance between two pointer touch points
*/
private static float spacing(MotionEvent event) {
float x = event.getX(0) - event.getX(1);
float y = event.getY(0) - event.getY(1);
return (float) Math.sqrt(x * x + y * y);
}
}
That class doesn't seem to be doing anything,How to set both axis's scales to be always the same?
Also, here is my chart class:
public class MathGraph extends LineChart {
public static final int BOUNDARIES = 100;
public static final int DATA_POINTS = 200;
private static final int LINE_WIDTH = 2;
private LineData data;
public MathGraph(Context context, AttributeSet attrs) {
super(context, attrs);
super.setDescription(null);
//Misc
getLegend().setEnabled(false);
setRenderer(new LineChatRendererNoData(this, mAnimator, mViewPortHandler));
//Lines encasing the chart
getXAxis().setAxisLineWidth(LINE_WIDTH);
getAxisLeft().setAxisLineWidth(LINE_WIDTH);
getAxisRight().setEnabled(false);
//Line for (x; 0)
getAxisLeft().setDrawZeroLine(true);
getAxisLeft().setZeroLineWidth(LINE_WIDTH);
getAxisRight().setDrawZeroLine(true);
getAxisRight().setZeroLineWidth(LINE_WIDTH);
//Line for (0; y)
LimitLine limitLine = new LimitLine(0f);
limitLine.setLineColor(Color.GRAY);
limitLine.setLineWidth(LINE_WIDTH);
getXAxis().addLimitLine(limitLine);
setOnChartGestureListener(new ZoomNotDistorting(this));
}
public void setFunction(Function f) {
if(!f.checkSyntax()) throw new IllegalStateException("Error in function: " + f.toString() + "!");
setDescription(f);
data = null;
LoadFunctionAsyncTask l = new LoadFunctionAsyncTask(f, -BOUNDARIES, BOUNDARIES, DATA_POINTS,
(List<Entry> pointList) -> {
if(data == null) {
ILineDataSet dataSet = new LineDataSet(new ArrayList<>(), null);
dataSet.setValueFormatter(new PointValueFormatter());
dataSet.setHighlightEnabled(true);
for (Entry dataPoint : pointList) {
dataSet.addEntry(dataPoint);
}
data = new LineData(dataSet);
setData(data);
} else {
for (Entry dataPoint : pointList) {
data.addEntry(dataPoint, 0);// 0 is the only dataset
}
data.notifyDataChanged();
notifyDataSetChanged();
invalidate();
}
});
l.execute();
}
private void setDescription(Function f) {
Description desc = new Description();
desc.setText(f.getDescription());
desc.setPosition(16, getBottom() - 16);
setDescription(desc);
}
private class PointValueFormatter implements IValueFormatter {
#Override
public String getFormattedValue(float value, Entry entry, int dataSetIndex, ViewPortHandler viewPortHandler) {
return "(" + entry.getX() + ", " + entry.getY() + ")";
}
}
}

Answer 1

OK, apparently chart.invalidate() isn't enough, the Matrix needs to be refreshed:
Matrix matrix = null;
//...
matrix = viewPortHandler.zoom(scaleX, scaleX);
//...
if(matrix != null) {
viewPortHandler.refresh(matrix, chart, true);
}
As a bonus, the last true in refresh() is for invalidate, so no need for chart.invalidate();.