Android: How to rotate a moving animated sprite ba

问题:

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.

回答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...

回答2:

using this referance to calculate Angle:

private double angleFromCoordinate(double lat1, double long1, double lat2,
        double long2) {

    double dLon = (long2 - long1);

    double y = Math.sin(dLon) * Math.cos(lat2);
    double x = Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1)
            * Math.cos(lat2) * Math.cos(dLon);

    double brng = Math.atan2(y, x);

    brng = Math.toDegrees(brng);
    brng = (brng + 360) % 360;
    brng = 360 - brng;

    return brng;
}

and then rotate ImageView to this angle

private void rotateImage(ImageView imageView, double angle) {

    Matrix matrix = new Matrix();
    imageView.setScaleType(ScaleType.MATRIX); // required
    matrix.postRotate((float) angle, imageView.getDrawable().getBounds()
            .width() / 2, imageView.getDrawable().getBounds().height() / 2);
    imageView.setImageMatrix(matrix);
}