Android image view matrix scale + translate

Question

I am trying to manually get an image inside an imageview centered and fitting the screen. I need to do it with a matrix (I will later dynamically change the matrix transform

Answer 1

Here is how I solved my problem using matrices (requested by joakime in the other answer):

private void setImageTransformation(float tx, float ty, float scale) {
    savedMatrix.reset();
    savedMatrix.postTranslate(-imageWidth / 2f, -imageHeight / 2f);
    savedMatrix.postScale(scale, scale);
    savedMatrix.postTranslate(tx, ty);
    imageView.setImageMatrix(savedMatrix);
}

public void resetImageMatrix() {
    if (!isImageLoaded()) return;

    imageWidth = imageView.getDrawable().getIntrinsicWidth();
    imageHeight = imageView.getDrawable().getIntrinsicHeight();

    float scaleX = (float) displayWidth / (float) imageWidth;
    float scaleY = (float) displayHeight / (float) imageHeight;
    minScale = Math.min(scaleX, scaleY);
    maxScale = 2.5f * minScale;

    initialTranslation.set(
              Math.max(0, 
                minScale * imageWidth / 2f 
                + 0.5f * (displayWidth - (minScale * imageWidth))), 
              Math.max(0, 
                minScale * imageHeight / 2f
                + 0.5f * (displayHeight - (minScale * imageHeight))));

    currentScale = minScale;
    currentTranslation.set(initialTranslation);
    initialImageRect.set(0, 0, imageWidth, imageHeight);

    setImageTransformation(initialTranslation.x, initialTranslation.y, 
                minScale);
}

I am cheating here a bit because the pinch is not really centered between the user fingers, which is acceptable in my case.