Android: How to Rotate a Bitmap on a Center Point

Android rotating bitmap around center point with cropping the corners

What helped my achieve the wanted result with good performance was switching from bitmap drawing to Google Maps, it's API has everything needed here

Android rotate bitmap around center without resizing

This worked for me!

I created a method that returns a matrix. The matrix can be used in the following drawing method:

public void drawBitmap (Bitmap bitmap, Matrix matrix, Paint paint)

Here you go! (The parameter shape can be replaced with ease, if you would like that, just leave a comment):

public static Matrix rotateMatrix(Bitmap bitmap, Shape shape, int rotation) {

        float scaleWidth = ((float) shape.getWidth()) / bitmap.getWidth();
        float scaleHeight = ((float) shape.getHeight()) / bitmap.getHeight();

        Matrix rotateMatrix = new Matrix();
        rotateMatrix.postScale(scaleWidth, scaleHeight);
        rotateMatrix.postRotate(rotation, shape.getWidth()/2, shape.getHeight()/2);
        rotateMatrix.postTranslate(shape.getX(), shape.getY());

        return rotateMatrix;

    }

NB: If you want an animated rotation, the rotation parameter will have to be updated with new values every frame eg. 1 then 2 then 3 ...

Rotating a Bitmap around a point NOT center to bitmap

After much messing around and find this very difficult or buggy, not sure which, found the easiest solution to this is to find the new center of the bitmap and drop the image there instead, seem more complicated but it works where plain rotation/translation wasn't.

  float angle;
  float radius;

  Bitmap wheelSelectBitmap = BitmapFactory.decodeResource(getResources(), R.drawable.image);
  Matrix matrix = new Matrix();

  Point pivotPoint = new Point();
  pivotPoint.set(pivotPoint.x, pivotPoint.y)
  Point newCenter = new Point();
  newCenter.set((int)(pivotPoint.x + (radius * Math.cos(angle)), (int)(pivotPoint.y - (radius * Math.sin(angle)));

  matrix.postTranslate(newCenter.x - (bitmap.getWidth()/2f), newCenter.y - (bitmap.getHeight()/2f));
  matrix.postRotate(angle, newCenter.x, newCenter.y);

  Bitmap rotatedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), null, true);
  canvas.drawBitmap(bitmap, matrix, null);

This might not be perfect but working this way solved the problem for me and stopped bitmaps flying around all over the shop. It also rotates clockwise by default unlike your diagram so just use -angle for counter-CW. Not sure what is going on here as this code definitely failed to get the desired effect for me:

 matrix.postTranslate(pivotPoint.x, pivotPoint.y);
 matrix.postRotate(angle);
 matrix.postTranslate(radius - (bitmap.getWidth()/2f), -bitmap.getHeight()/2f);

Cant see what is wrong with logic here ? But in my case the bitmap was not visible in the view here.

Rotate bitmap in fixed point like a clock hand in SurfaceView

I found the answer. Let px and py be any point on canvas. bitmap.getWidth()/2 is middle point along bitmap width. It can be any point for x cordinate. For y cordinate I have taken it as 10. angleRotation is the angle that is as per required.

So matrix.postTranslate(-bitmap.getWidth()/2, -10); is the point of rotation.

Below is the code.

        Matrix matrix = new Matrix();
        matrix.reset();
        Paint paint = new Paint();
        float px = 240;
        float py = 480;
        matrix.postTranslate(-bitmap.getWidth()/2, -10);
        matrix.postRotate(angleRotation);
        matrix.postTranslate(px, py);
        canvas.drawBitmap(bitmap, matrix, paint);

Above code satisfy my requirements. Please modify it as per your need.

How to rotate a bitmap in Android about images center smoothly without oscillatory movement

Here is an example.
I broke it to 3 steps.
The first translate moves the bitmap so that it's center is at 0,0
Then a rotation,
and finally move the bitmap center to where you want it on the canvas.
You don't need the second bitmap.

Matrix matrix = new Matrix();
rotation += 10;
float px = this.viewWidth/2;
float py = this.viewHeight/2;
matrix.postTranslate(-bitmap.getWidth()/2, -bitmap.getHeight()/2);
matrix.postRotate(rotation);
matrix.postTranslate(px, py);
canvas.drawBitmap(bitmap, matrix, null);

As an optimization, create the Matrix once outside this method and replace the creation with a call to matrix.reset()

rotate image in around its center point in canvas

You can use a matrix to rotate. First you set the position (I'm using the coordinates of the bitmap's centre). Then apply a rotation. Then draw using your matrix.

    Matrix transform = new Matrix();
    transform.setTranslate(xOfCentre, yOfCentre);
    transform.preRotate(turnDegrees, width/2, height/2);
    canvas.drawBitmap(bitmap, transform, null);

If you want your turning to be animated, then see my answer to "animating and rotating an image...".

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