问题
How can I obtain the corresponding x-axis value (xIndex) of a pixel point in a ScatterChart?
I have been looking through the source code of the library and I think that one of the methods below (which I copy/pasted from the source code from the library here) can help. It seems getValuesByTouchPoint is the correct method but I don't know how to use it.
/**
* Transformer class that contains all matrices and is responsible for
* transforming values into pixels on the screen and backwards.
*
* @author Philipp Jahoda
*/
public class Transformer {
/**
* matrix to map the values to the screen pixels
*/
protected Matrix mMatrixValueToPx = new Matrix();
/**
* matrix for handling the different offsets of the chart
*/
protected Matrix mMatrixOffset = new Matrix();
protected ViewPortHandler mViewPortHandler;
public Transformer(ViewPortHandler viewPortHandler) {
this.mViewPortHandler = viewPortHandler;
}
/**
* Prepares the matrix that transforms values to pixels. Calculates the
* scale factors from the charts size and offsets.
*
* @param xChartMin
* @param deltaX
* @param deltaY
* @param yChartMin
*/
public void prepareMatrixValuePx(float xChartMin, float deltaX, float deltaY, float yChartMin) {
float scaleX = (float) ((mViewPortHandler.contentWidth()) / deltaX);
float scaleY = (float) ((mViewPortHandler.contentHeight()) / deltaY);
if (Float.isInfinite(scaleX)) {
scaleX = 0;
}
if (Float.isInfinite(scaleY)) {
scaleY = 0;
}
// setup all matrices
mMatrixValueToPx.reset();
mMatrixValueToPx.postTranslate(-xChartMin, -yChartMin);
mMatrixValueToPx.postScale(scaleX, -scaleY);
}
/**
* Prepares the matrix that contains all offsets.
*
* @param inverted
*/
public void prepareMatrixOffset(boolean inverted) {
mMatrixOffset.reset();
// offset.postTranslate(mOffsetLeft, getHeight() - mOffsetBottom);
if (!inverted)
mMatrixOffset.postTranslate(mViewPortHandler.offsetLeft(),
mViewPortHandler.getChartHeight() - mViewPortHandler.offsetBottom());
else {
mMatrixOffset
.setTranslate(mViewPortHandler.offsetLeft(), -mViewPortHandler.offsetTop());
mMatrixOffset.postScale(1.0f, -1.0f);
}
}
protected float[] valuePointsForGenerateTransformedValuesScatter = new float[1];
/**
* Transforms an List of Entry into a float array containing the x and
* y values transformed with all matrices for the SCATTERCHART.
*
* @param data
* @return
*/
public float[] generateTransformedValuesScatter(IScatterDataSet data, float phaseX,
float phaseY, int from, int to) {
final int count = (int) ((to - from) * phaseX + 1) * 2;
if (valuePointsForGenerateTransformedValuesScatter.length != count) {
valuePointsForGenerateTransformedValuesScatter = new float[count];
}
float[] valuePoints = valuePointsForGenerateTransformedValuesScatter;
for (int j = 0; j < count; j += 2) {
Entry e = data.getEntryForIndex(j / 2 + from);
if (e != null) {
valuePoints[j] = e.getX();
valuePoints[j + 1] = e.getY() * phaseY;
} else {
valuePoints[j] = 0;
valuePoints[j + 1] = 0;
}
}
getValueToPixelMatrix().mapPoints(valuePoints);
return valuePoints;
}
protected float[] valuePointsForGenerateTransformedValuesBubble = new float[1];
/**
* Transforms an List of Entry into a float array containing the x and
* y values transformed with all matrices for the BUBBLECHART.
*
* @param data
* @return
*/
public float[] generateTransformedValuesBubble(IBubbleDataSet data, float phaseY, int from, int to) {
final int count = (to - from + 1) * 2; // (int) Math.ceil((to - from) * phaseX) * 2;
if (valuePointsForGenerateTransformedValuesBubble.length != count) {
valuePointsForGenerateTransformedValuesBubble = new float[count];
}
float[] valuePoints = valuePointsForGenerateTransformedValuesBubble;
for (int j = 0; j < count; j += 2) {
Entry e = data.getEntryForIndex(j / 2 + from);
if (e != null) {
valuePoints[j] = e.getX();
valuePoints[j + 1] = e.getY() * phaseY;
} else {
valuePoints[j] = 0;
valuePoints[j + 1] = 0;
}
}
getValueToPixelMatrix().mapPoints(valuePoints);
return valuePoints;
}
protected float[] valuePointsForGenerateTransformedValuesLine = new float[1];
/**
* Transforms an List of Entry into a float array containing the x and
* y values transformed with all matrices for the LINECHART.
*
* @param data
* @return
*/
public float[] generateTransformedValuesLine(ILineDataSet data,
float phaseX, float phaseY, int from, int to) {
final int count = (int) ((to - from) * phaseX + 1) * 2;
if (valuePointsForGenerateTransformedValuesLine.length != count) {
valuePointsForGenerateTransformedValuesLine = new float[count];
}
float[] valuePoints = valuePointsForGenerateTransformedValuesLine;
for (int j = 0; j < count; j += 2) {
Entry e = data.getEntryForIndex(j / 2 + from);
if (e != null) {
valuePoints[j] = e.getX();
valuePoints[j + 1] = e.getY() * phaseY;
} else {
valuePoints[j] = 0;
valuePoints[j + 1] = 0;
}
}
getValueToPixelMatrix().mapPoints(valuePoints);
return valuePoints;
}
protected float[] valuePointsForGenerateTransformedValuesCandle = new float[1];
/**
* Transforms an List of Entry into a float array containing the x and
* y values transformed with all matrices for the CANDLESTICKCHART.
*
* @param data
* @return
*/
public float[] generateTransformedValuesCandle(ICandleDataSet data,
float phaseX, float phaseY, int from, int to) {
final int count = (int) ((to - from) * phaseX + 1) * 2;
if (valuePointsForGenerateTransformedValuesCandle.length != count) {
valuePointsForGenerateTransformedValuesCandle = new float[count];
}
float[] valuePoints = valuePointsForGenerateTransformedValuesCandle;
for (int j = 0; j < count; j += 2) {
CandleEntry e = data.getEntryForIndex(j / 2 + from);
if (e != null) {
valuePoints[j] = e.getX();
valuePoints[j + 1] = e.getHigh() * phaseY;
} else {
valuePoints[j] = 0;
valuePoints[j + 1] = 0;
}
}
getValueToPixelMatrix().mapPoints(valuePoints);
return valuePoints;
}
/**
* transform a path with all the given matrices VERY IMPORTANT: keep order
* to value-touch-offset
*
* @param path
*/
public void pathValueToPixel(Path path) {
path.transform(mMatrixValueToPx);
path.transform(mViewPortHandler.getMatrixTouch());
path.transform(mMatrixOffset);
}
/**
* Transforms multiple paths will all matrices.
*
* @param paths
*/
public void pathValuesToPixel(List<Path> paths) {
for (int i = 0; i < paths.size(); i++) {
pathValueToPixel(paths.get(i));
}
}
/**
* Transform an array of points with all matrices. VERY IMPORTANT: Keep
* matrix order "value-touch-offset" when transforming.
*
* @param pts
*/
public void pointValuesToPixel(float[] pts) {
mMatrixValueToPx.mapPoints(pts);
mViewPortHandler.getMatrixTouch().mapPoints(pts);
mMatrixOffset.mapPoints(pts);
}
/**
* Transform a rectangle with all matrices.
*
* @param r
*/
public void rectValueToPixel(RectF r) {
mMatrixValueToPx.mapRect(r);
mViewPortHandler.getMatrixTouch().mapRect(r);
mMatrixOffset.mapRect(r);
}
/**
* Transform a rectangle with all matrices with potential animation phases.
*
* @param r
* @param phaseY
*/
public void rectToPixelPhase(RectF r, float phaseY) {
// multiply the height of the rect with the phase
r.top *= phaseY;
r.bottom *= phaseY;
mMatrixValueToPx.mapRect(r);
mViewPortHandler.getMatrixTouch().mapRect(r);
mMatrixOffset.mapRect(r);
}
public void rectToPixelPhaseHorizontal(RectF r, float phaseY) {
// multiply the height of the rect with the phase
r.left *= phaseY;
r.right *= phaseY;
mMatrixValueToPx.mapRect(r);
mViewPortHandler.getMatrixTouch().mapRect(r);
mMatrixOffset.mapRect(r);
}
/**
* Transform a rectangle with all matrices with potential animation phases.
*
* @param r
*/
public void rectValueToPixelHorizontal(RectF r) {
mMatrixValueToPx.mapRect(r);
mViewPortHandler.getMatrixTouch().mapRect(r);
mMatrixOffset.mapRect(r);
}
/**
* Transform a rectangle with all matrices with potential animation phases.
*
* @param r
* @param phaseY
*/
public void rectValueToPixelHorizontal(RectF r, float phaseY) {
// multiply the height of the rect with the phase
r.left *= phaseY;
r.right *= phaseY;
mMatrixValueToPx.mapRect(r);
mViewPortHandler.getMatrixTouch().mapRect(r);
mMatrixOffset.mapRect(r);
}
/**
* transforms multiple rects with all matrices
*
* @param rects
*/
public void rectValuesToPixel(List<RectF> rects) {
Matrix m = getValueToPixelMatrix();
for (int i = 0; i < rects.size(); i++)
m.mapRect(rects.get(i));
}
protected Matrix mPixelToValueMatrixBuffer = new Matrix();
/**
* Transforms the given array of touch positions (pixels) (x, y, x, y, ...)
* into values on the chart.
*
* @param pixels
*/
public void pixelsToValue(float[] pixels) {
Matrix tmp = mPixelToValueMatrixBuffer;
tmp.reset();
// invert all matrixes to convert back to the original value
mMatrixOffset.invert(tmp);
tmp.mapPoints(pixels);
mViewPortHandler.getMatrixTouch().invert(tmp);
tmp.mapPoints(pixels);
mMatrixValueToPx.invert(tmp);
tmp.mapPoints(pixels);
}
/**
* buffer for performance
*/
float[] ptsBuffer = new float[2];
/**
* Returns a recyclable MPPointD instance.
* returns the x and y values in the chart at the given touch point
* (encapsulated in a MPPointD). This method transforms pixel coordinates to
* coordinates / values in the chart. This is the opposite method to
* getPixelForValues(...).
*
* @param x
* @param y
* @return
*/
public MPPointD getValuesByTouchPoint(float x, float y) {
MPPointD result = MPPointD.getInstance(0, 0);
getValuesByTouchPoint(x, y, result);
return result;
}
public void getValuesByTouchPoint(float x, float y, MPPointD outputPoint) {
ptsBuffer[0] = x;
ptsBuffer[1] = y;
pixelsToValue(ptsBuffer);
outputPoint.x = ptsBuffer[0];
outputPoint.y = ptsBuffer[1];
}
/**
* Returns a recyclable MPPointD instance.
* Returns the x and y coordinates (pixels) for a given x and y value in the chart.
*
* @param x
* @param y
* @return
*/
public MPPointD getPixelForValues(float x, float y) {
ptsBuffer[0] = x;
ptsBuffer[1] = y;
pointValuesToPixel(ptsBuffer);
double xPx = ptsBuffer[0];
double yPx = ptsBuffer[1];
return MPPointD.getInstance(xPx, yPx);
}
public Matrix getValueMatrix() {
return mMatrixValueToPx;
}
public Matrix getOffsetMatrix() {
return mMatrixOffset;
}
private Matrix mMBuffer1 = new Matrix();
public Matrix getValueToPixelMatrix() {
mMBuffer1.set(mMatrixValueToPx);
mMBuffer1.postConcat(mViewPortHandler.mMatrixTouch);
mMBuffer1.postConcat(mMatrixOffset);
return mMBuffer1;
}
private Matrix mMBuffer2 = new Matrix();
public Matrix getPixelToValueMatrix() {
getValueToPixelMatrix().invert(mMBuffer2);
return mMBuffer2;
}
}
回答1:
Using MPAndroidChart 3.0.1
I think the method you want is:
public MPPointD getValuesByTouchPoint(float x, float y);
Here's a snip from the javadoc:
/**
* Returns a recyclable MPPointD instance.
* returns the x and y values in the chart at the given touch point
* (encapsulated in a MPPointD). This method transforms pixel coordinates to
* coordinates / values in the chart. This is the opposite method to
* getPixelsForValues(...).
To use it in your app, do something like this:
MPPointD point = mChart.getTransformer(AxisDependency.LEFT).getValuesByTouchPoint(x,y);
double xValue = point.x;
double yValue = point.y;
The parameters passed into the method (float x, float y) are your pixel co-ordinates that you want to be converted into x and y values in your chart.
来源：https://stackoverflow.com/questions/41766419/mpandroidchart-how-do-i-get-the-corresponding-chart-x-value-for-a-pixel-point