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.

Answer 2

Or using

    m.postScale(minScale, minScale); //keep aspect ratio

    float tx = (getWidth() - bitmap1.getWidth()* scale) * 0.5f ;
    float ty = (getHeight() - bitmap1.getHeight()* scale) * 0.5f ;

    matrix.postTranslate(tx, ty );

where getWidth is the width of your imageView. Works perfectly for me

Answer 3

There's a convenient method called Matrix.setRectToRect(RectF, RectF, ScaleToFit) to help you here.

Matrix m = imageView.getImageMatrix();
RectF drawableRect = new RectF(0, 0, imageWidth, imageHeight);
RectF viewRect = new RectF(0, 0, imageView.getWidth(), imageView.getHeight());
m.setRectToRect(drawableRect, viewRect, Matrix.ScaleToFit.CENTER);
imageView.setImageMatrix(m);

That should set the matrix m to have combo of scaling and translate values that is needed to show the drawable centered and fit within the ImageView widget.

Answer 4

Hey I was having the same issue, and you were oh so close! It was an order of operations issue, at least for me. The following worked for me:

tx = (width - imgWidth) * 0.5f * scale;