Drift in rotation about z-axis

问题

In an application, while trying to rotate an object using touch, I noticed drift in position of object after sometime (without any translation applied !!). The rotation is only about z-axis and works perfectly, but drift happens only after few rotations.

ds will be used for translation (using up-down button).

_uNozzleCentreMatrix and _ModelMatrixNozzle will use ds if I correct this.

private static final float[] _uNozzleCentre     = new float[]{0.0f, 0.333605f, 0.0f, 1.0f};
protected static float[] _uNozzleCentreMatrix   = new float[4];

public void onSurfaceChanged(GL10 gl, int width, int height) {
    gl.glViewport(0, 0, width, height);
    float ratio = (float) width / height;
    Matrix.setLookAtM(GLES20Renderer._ViewMatrix, 0, 0, 0, 7f, 0, 0, 0, 0, 1, 0);
    Matrix.frustumM(GLES20Renderer._ProjectionMatrix, 0, -ratio, ratio, -1, 1, 2, 8);
    Matrix.setIdentityM(GLES20Renderer._ModelMatrixNozzle, 0);
}
private static void updateModel(int upDown, float xAngle, float yAngle, float zAngle) {
    //ds                = GLES20Renderer._upDown - GLES20Renderer._lastUpDown;
    ds = 0; // ds changes with button up-down, but now it is made 0, so button up-down will not affect it
    Matrix.multiplyMV(GLES20Renderer._uNozzleCentreMatrix, 0, GLES20Renderer._ModelMatrixNozzle, 0, GLES20Renderer._uNozzleCentre, 0);
    if(Math.abs(ds) > 0) {
    } else {
        if(GLES20Renderer._zAngle >= 360) {
            GLES20Renderer._zAngle = GLES20Renderer._zAngle - 360;
        }
        if(GLES20Renderer._zAngle <= -360) {
            GLES20Renderer._zAngle = GLES20Renderer._zAngle + 360;
        }
        Matrix.translateM(GLES20Renderer._ModelMatrixNozzle, 0, GLES20Renderer._uNozzleCentreMatrix[0], GLES20Renderer._uNozzleCentreMatrix[1], 0);
        Matrix.rotateM(GLES20Renderer._ModelMatrixNozzle, 0, GLES20Renderer._zAngle, 0, 0, 1);
        Matrix.rotateM(GLES20Renderer._ModelMatrixNozzle, 0, -GLES20Renderer._lastZAngle, 0, 0, 1);
        Matrix.translateM(GLES20Renderer._ModelMatrixNozzle, 0, -GLES20Renderer._uNozzleCentreMatrix[0], -GLES20Renderer._uNozzleCentreMatrix[1], 0);
    }
    Matrix.multiplyMM(GLES20Renderer._MVPMatrixNozzle, 0, GLES20Renderer._ViewMatrix, 0, GLES20Renderer._ModelMatrixNozzle, 0);
    Matrix.multiplyMM(GLES20Renderer._MVPMatrixNozzle, 0, GLES20Renderer._ProjectionMatrix, 0, GLES20Renderer._MVPMatrixNozzle, 0);

    GLES20Renderer._lastZAngle = zAngle;
}

Apk for download:

http://www.pixdip.com/opengles/rotation/rotation.apk

(Try swiping a longer horizontal area from extreme left to right to observe drift early. Please be patient! Drift can take 20 seconds to occur)

For those whom it did not happen, here is the automated apk: http://www.pixdip.com/opengles/rotation/automatic.apk

and the edited part of code:

        Matrix.translateM(GLES20Renderer._ModelMatrixNozzle, 0, GLES20Renderer._uNozzleCentreMatrix[0], GLES20Renderer._uNozzleCentreMatrix[1], 0);
        Matrix.rotateM(GLES20Renderer._ModelMatrixNozzle, 0, GLES20Renderer._zAngle, 0, 0, 1);
        //Matrix.rotateM(GLES20Renderer._ModelMatrixNozzle, 0, -GLES20Renderer._lastZAngle, 0, 0, 1);
        Matrix.translateM(GLES20Renderer._ModelMatrixNozzle, 0, -GLES20Renderer._uNozzleCentreMatrix[0], -GLES20Renderer._uNozzleCentreMatrix[1], 0);

回答1:

Sometimes floating point errors get accumulated because of matrix stack.

This can be removed by using separate matrices for some critical transformations:

private static float[] _TMatrix = new float[16];
private static float[] _ModelMatrix = new float[16];
Matrix.setIdentity(Renderer._ModelMatrix);
Matrix.setIdentity(Renderer._TMatrix);
Matrix.translate(Renderer._ModelMatrix, xmov,ymov,0);
Matrix.translate(Renderer._TMatrix, -xmov,-ymov,0);
Matrix.multiply(Renderer._ModelMatrix, Renderer._TMatrix, Renderer._ModelMatrix);
// will result in an identity model matrix, without any floating point errors

来源：https://stackoverflow.com/questions/12196614/drift-in-rotation-about-z-axis