在Android中旋转图像的问题

Question

I am facing problme in rotating image

Following code works fine

Matrix matrix = new Matrix();
matrix.postRotate(DEGREE,mBitmap.getWidth() / 2, mBitmap.getHeight() / 2);
Bitmap m = Bitmap.createBitmap(mBitmap, 0, 0, mBitmap.getWidth(),mBitmap.getHeight(), matrix, true);
canvas.drawBitmap(m, mX, mY, null);

But I dont want to create a new bitmap again and again so I am using the following code

Matrix matrix = new Matrix();
matrix.postTranslate(mX, mY);
matrix.postRotate(DEGREE,mBitmap.getWidth() / 2, mBitmap.getHeight() / 2);
canvas.drawBitmap(mBitmap, matrix, null);

In that case image goes out of the view. It is not visible.

Answer 1

Matrix matrix = new Matrix();
canvas.translate(mX, mY);
canvas.drawBitmap(...);
canvas.translate(-mX, -mY);

Answer 2

尝试先旋转它，然后再平移它，因为当您首先平移它时，中心不再在中间，因此您使用错误的枢轴坐标旋转它。

Answer 3

The pivot point by default when rotating is the top left corner of the image, which is why the view goes out of view. You need to add logic to make the pivot point the center of the image. Unfortunately, geometry is not my strong suit so maybe someone who somewhat enjoys geometry can give you the calculations to make this happen.