Flip a Bitmap image horizontally or vertically

Question

By using this code we can rotate an image:

public static Bitmap RotateBitmap(Bitmap source, float angle) {       Matrix matrix = new Matrix();       matrix.postRotate(angle);       return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), matrix, true); } 

But how can we flip an image horizontally or vertically?

Answer 1

Given cx,cy is the centre of the image:

Flip in x:

matrix.postScale(-1, 1, cx, cy); 

Flip in y:

matrix.postScale(1, -1, cx, cy); 

Altogether:

public static Bitmap createFlippedBitmap(Bitmap source, boolean xFlip, boolean yFlip) {     Matrix matrix = new Matrix();     matrix.postScale(xFlip ? -1 : 1, yFlip ? -1 : 1, source.getWidth() / 2f, source.getHeight() / 2f);     return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), matrix, true); } 

Answer 2

Short extension for Kotlin

private fun Bitmap.flip(x: Float, y: Float, cx: Float, cy: Float): Bitmap {     val matrix = Matrix().apply { postScale(x, y, cx, cy) }     return Bitmap.createBitmap(this, 0, 0, width, height, matrix, true) } 

And usage:

For horizontal flip :-

val cx = bitmap.width / 2f val cy = bitmap.height / 2f val flippedBitmap = bitmap.flip(-1f, 1f, cx, cy) ivMainImage.setImageBitmap(flippedBitmap) 

For vertical flip :-

val cx = bitmap.width / 2f val cy = bitmap.height / 2f val flippedBitmap = bitmap.flip(1f, -1f, cx, cy) ivMainImage.setImageBitmap(flippedBitmap)