canvas.scale 与枢轴，鼠标坐标

Question

I've been trying to get the mouse coordinates from scaled canvas. The canvas.scale(scale, scale) gives me the correct coordinates but if i use canvas.scale(scale, scale, pivotX, pivotY) the coordinates are wrong.

//onDraw
canvas.scale(scaleFactor, scaleFactor); //default pivot x & y = 0, 0
//canvas.scale(scaleFactor, scaleFactor, pivotX, pivotY);

private float pixelWidth = 480;
private float pixelHeight = 320; 

//onTouchEvent
touchX = (int) event.getX() * pixelWidth / getWidth();
touchX = (int) event.getY() * pixelHeight / getHeight();

worldX = touchX / scaleFactor;
worldY = touchY / scaleFactor;

What do i need to do to get the correct coordinates from canvas.scale with different pivot other than default 0, 0? I've read & tried about the matrix too but no luck.

Answer 1

solved it using matrix and this code from https://stackoverflow.com/a/20011005/7334711

Matrix matrix = new Matrix();

public void render(Canvas canvas) {
    canvas.save();

    matrix.setScale(mScaleFactor, mScaleFactor, pivotX, pivotY);
    canvas.setMatrix(matrix);
...

float[] mv = new float[9];

@Override
public boolean onTouchEvent(MotionEvent event) {

    // Get the values from the matrix into the float array
    matrix.getValues(mv);

    float touchX = (event.getX()*(1/mv[4]) - (mv[2]/mv[4]));
    float touchY = (event.getY()*(1/mv[4]) - (mv[5]/mv[4]));
...