how to rotate a bitmap 90 degrees

Question

There is a statement in android canvas.drawBitmap(visiblePage, 0, 0, paint);

When I add canvas.rotate(90), there is no effect. But if I wri

Answer 1

Just be careful of Bitmap type from java platform call like from comm1x's and Gnzlt's answers, because it might return null. I think it is also more flexible if the parameter can be any Number and use infix for readability, depends on your coding style.

infix fun Bitmap.rotate(degrees: Number): Bitmap? {
    return Bitmap.createBitmap(
        this,
        0,
        0,
        width,
        height,
        Matrix().apply { postRotate(degrees.toFloat()) },
        true
    )
}

How to use?

bitmap rotate 90
// or
bitmap.rotate(90)

Answer 2

If you rotate bitmap, 90 180 270 360 is ok but for other degrees canvas will draw bitmap with different size.

So,the best way is

canvas.rotate(degree,rotateCenterPoint.x,rotateCenterPoint.y);  
canvas.drawBitmap(...);
canvas.rotate(-degree,rotateCenterPoint.x,rotateCenterPoint.y);//rotate back

Answer 3

Using Java createBitmap() method you can pass the degrees.

Bitmap bInput /*your input bitmap*/, bOutput;
float degrees = 45; //rotation degree
Matrix matrix = new Matrix();
matrix.setRotate(degrees);
bOutput = Bitmap.createBitmap(bInput, 0, 0, bInput.getWidth(), bInput.getHeight(), matrix, true);

Answer 4

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);
}

To get Bitmap from resources:

Bitmap source = BitmapFactory.decodeResource(this.getResources(), R.drawable.your_img);

Answer 5

Short extension for Kotlin

fun Bitmap.rotate(degrees: Float): Bitmap {
    val matrix = Matrix().apply { postRotate(degrees) }
    return Bitmap.createBitmap(this, 0, 0, width, height, matrix, true)
}

And usage:

val rotatedBitmap = bitmap.rotate(90f)

Answer 6

I would simplify comm1x's Kotlin extension function even more:

fun Bitmap.rotate(degrees: Float) =
    Bitmap.createBitmap(this, 0, 0, width, height, Matrix().apply { postRotate(degrees) }, true)