Question

My application fires up sprite instances around a Canvas which then move across the screen towards a x/y coordinate. I would like to be able to rotate the sprite around its center so that it faces its destination coordinates. I am using a sprite-sheet and have had issues with clipping. I have also found a lot of good examples but nothing seems to cover exactly what I’m looking for. This example is very close but for efficiency I am using an ImagePooler class and cannot reload an image on each draw/rotation. So if someone had an idea on how to rotate the preloaded image w/out cutting my sprite-sheet I would be very grateful.

Answer 1

First it is easy to rotate a sprite you can use canvas or matrix:

Matrix matrix = new Matrix();
matrix.postRotate(angle, (ballW / 2), (ballH / 2)); //rotate it
matrix.postTranslate(X, Y); //move it into x, y position
canvas.drawBitmap(ball, matrix, null); //draw the ball with the applied matrix

// method two 
canvas.save(); //save the position of the canvas
canvas.rotate(angle, X + (ballW / 2), Y + (ballH / 2)); //rotate the canvas' matrix
canvas.drawBitmap(ball, X, Y, null); //draw the ball on the "rotated" canvas
canvas.restore(); //rotate the canvas' matrix back
//in the second method only the ball was roteded not the entire canvas

To turn it towards a destination you need to know the angle between the sprite and the destination:

spriteToDestAngle =  Math.toDegrees(Math.atan2((spriteX - destX)/(spriteY - destY)));

Now all you need to do is to use this angle for the sprite rotation plus ajust it with a constant like angleShift which depends to where your sprite initially points.

I am not sure if this will work but hope it may give you some ideas…