How to convert coordinates of the image view to the coordinates of the bitmap?

Question

In my app I need to let users to check the eyes at some photo. In OnTouchListener.onTouch(...) I get the coordinates of the ImageView.

How can I convert this coordinates to the point at the bitmap that was touched?

Answer 1

this works for me at least with API 10+:

final float[] getPointerCoords(ImageView view, MotionEvent e)
{
    final int index = e.getActionIndex();
    final float[] coords = new float[] { e.getX(index), e.getY(index) };
    Matrix matrix = new Matrix();
    view.getImageMatrix().invert(matrix);
    matrix.postTranslate(view.getScrollX(), view.getScrollY());
    matrix.mapPoints(coords);
    return coords;
}

Answer 2

Okay, so I've not tried this, but giving it a bit of thought, here's what I've got as a suggestion:

ImageView imageView = (ImageView)findViewById(R.id.imageview);
Drawable drawable = imageView.getDrawable();
Rect imageBounds = drawable.getBounds();

//original height and width of the bitmap
int intrinsicHeight = drawable.getIntrinsicHeight();
int intrinsicWidth = drawable.getIntrinsicWidth();

//height and width of the visible (scaled) image
int scaledHeight = imageBounds.height();
int scaledWidth = imageBounds.width();

//Find the ratio of the original image to the scaled image
//Should normally be equal unless a disproportionate scaling
//(e.g. fitXY) is used.
float heightRatio = intrinsicHeight / scaledHeight;
float widthRatio = intrinsicWidth / scaledWidth;

//do whatever magic to get your touch point
//MotionEvent event;

//get the distance from the left and top of the image bounds
int scaledImageOffsetX = event.getX() - imageBounds.left;
int scaledImageOffsetY = event.getY() - imageBounds.top;

//scale these distances according to the ratio of your scaling
//For example, if the original image is 1.5x the size of the scaled
//image, and your offset is (10, 20), your original image offset
//values should be (15, 30). 
int originalImageOffsetX = scaledImageOffsetX * widthRatio;
int originalImageOffsetY = scaledImageOffsetY * heightRatio;

Give this idea a try and see if it works for you.