Develop Reference

Rotating Bitmap Not Rotating

I have tried several hours to rotate a bitmap with no success. I have read numerous articles about this subject on this web site and it seems the prefered solution involves creating a temporary canvas. Well I did this and I still do not see a roated bitmap.
My bitmap is a 40x40 blue square and I am trying to rotate it 45 degrees. Thats not asking for much is it? When the code runs, the bitmap that appears on the screen is the non-rotated original. ( I have also tried a translate with no success as well)
Here is my code:
// Load the bitmap resource
fillBMP2 = BitmapFactory.decodeResource(context.getResources(), R.drawable.test1);
// Copy to a mutable bitmap
mb = fillBMP2.copy(Bitmap.Config.ARGB_8888, true);
// Create canvas to draw to
Canvas offscreenCanvas = new Canvas (mb);
// Create Matrix so I can rotate it
Matrix matrix = new Matrix();
matrix.setRotate (45);
offscreenCanvas.setMatrix (matrix);
// Send the contents of the canvas into a bitmap
offscreenCanvas.setBitmap(mb);
Later in an OnDraw I do the following:
canvas.drawBitmap(mb, 200, 200, null);
Any ideas what I am doing wrong? Seems like it should work.
Thanks

Try using this
Matrix matrix = new Matrix();
matrix.setRotate(15);
canvas.drawBitmap(bmp, matrix, paint);
setRotation method takes in a float representing
the degrees of rotation.

Try this...
Matrix matrix = new Matrix();
float px = 200;
float py = 200;
matrix.postTranslate(-bitmap.getWidth()/2, -bitmap.getWidth()/2);
matrix.postRotate(45);
matrix.postTranslate(px, py);
canvas.drawBitmap(bitmap, matrix, paint);

You definitely want to use transformations: check out this link.
Basically it's this:
// save the canvas
ctx.save();
// move origin to center
ctx.translate(x,y);
// rotate
ctx.rotate(angle * (Math.PI / 180));
// draw image
ctx.drawImage(image, x, y, w, h, .w/2, h/2, w, h);
// restore
ctx.restore();

Inverse drawing of Bitmap on Canvas

How can I inverse the image drawed into a Canvas?
I has the following:
canvas.save();
canvas.drawBitmap(image.current(), null, currentBounds(), Paints.BLANK);
canvas.restore();
How can I make the current image be drawed fliped on x-axis into the currentBounds()?
I already found some answers indicating usage of Matrix, but I wan't to know if there's a easier way? Such a Paint with some flag turned on.
EDIT:
Following is my try with Matrix transformations:
Rect currentBounds = currentBounds();
currentBounds.offset((int)offset.x(), (int)offset.y());
float scale = image.current().getWidth() / currentBounds.width();
Matrix matrix = new Matrix();
matrix.setScale(- scale - 1, scale + 1);
matrix.postTranslate(currentBounds.left, currentBounds.top);
canvas.drawBitmap(image.current(), matrix, Paints.BLANK);
canvas.drawRect(currentBounds, Paints.STROKE_BLUE);
The following is the result of this draw:
https://dl.dropbox.com/u/28683814/game.png
As can be seen, the sprite is being drawed from 0,0 to left and it's not fully completes the currentBounds(), what I'm doing wrong?

Use
canvas.scale(-1,0,width/2,height/2);
as mentioned by my own answer here.
Although, I would point out that it will take you about a minute to understand Matrices, and it'll make you a better Android programmer.

Use this. I think this is quite easy.
canvas.save();
canvas.rotate(180, x, y);
canvas.drawBitmap(bitmap, x, y, null);
canvas.restore();

Well, I solved this way:
Rect currentBounds = currentBounds();
currentBounds.offset((int)offset.x(), (int)offset.y());
float scale = (float) currentBounds.width() / (float) image.current().getWidth();
boolean leftMovement = movingLeft();
Matrix matrix = new Matrix();
matrix.setScale(leftMovement ? -scale : scale, scale);
matrix.postTranslate(leftMovement ? currentBounds.right : currentBounds.left, currentBounds.top);
canvas.drawBitmap(image.current(), matrix, Paints.BLANK);
But this "leftMovement ? currentBounds.right : currentBounds.left" does not looks right

Rotating an image around a pivot point

The issue is simple: I want to rotate an image around a certain pivot point. Here is the code I use:
Matrix matrix = new Matrix();
matrix.setTranslate(bmpWidth/2, 0);
matrix.preRotate(degrees, bmpWidth/2, 0);
Bitmap resizedBitmap = Bitmap.createBitmap(
bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
ImageView imageView = (ImageView) findViewById(R.id.bell);
imageView.setImageBitmap(resizedBitmap);
I get the rotation degrees from the accelerometer sensor. The result is that every time the image is rotated around its center point.

I think you should try doing this:
imageView.setPivotX(desiredXPivotPoint);
imageView.setPivotY(desiredYPivotPoint);
That should do the trick.

This is kinda old, but there is a function that allows you to specify both the degrees of rotation as well as the pivot point:
imageView.setRotation(degrees, px, py)

Problem in rotating image in android

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.

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

Try first rotating it then translating it, because when you translate it first the center is not in the middle any more so you are rotating it with wrong pivot coordinates.

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.

Rotating a bitmap on an axis in Android

I have a bitmap flush with the bottom of my screen. When the user clicks a button I want it to rotate to the right by one degree. I am able to accomplish this but the problem is that the bottom of the item is no longer flush with the screen. I need it to appear to rotate on its bottom axis. I could use some hack to increment the x and y when its rotated (using trial and error I suppose) but is there a formula or something more elegant I can use?
public void rotate(int degrees)
{
Matrix mat = new Matrix();
mat.postRotate(degrees);
bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), mat, true);
}

Could you not instead use the following method that Matrix also has:
postRotate (float degrees, float px, float py)
It enables rotation on the specified point.