使用滚动opengl ES围绕场景旋转相机

Question

我正在尝试使用触摸（滚动）围绕场景旋转相机：

public class SurfaceView extends GLSurfaceView 
        implements GestureDetector.OnGestureListener {
    SceneRenderer renderer;        

    @Override
    public boolean onScroll(MotionEvent e1, MotionEvent e2,
                      float distanceX, float distanceY) {
        renderer.setMotion(distanceX, distanceY); // pass movement to render
        return true;
    }    
}

相机在渲染中移动如下：

public class SceneRenderer implements GLSurfaceView.Renderer {
    private float[] viewMatrix = new float[16];
    
    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        Matrix.setLookAtM(viewMatrix, 0, 0f, 0f, 3f,
        0f, 0f, 0f, 0f, 1.0f, 0.0f);
    }

    ...
    // movement of camera
    public synchronized void setMotion(float xDistance, float yDistance) {
        Matrix.rotateM(viewMatrix, 0, -xDistance * 0.1f, 0, 1, 0);
        Matrix.rotateM(viewMatrix, 0, -yDistance * 0.1f, 1, 0, 0);
    }
}

这在开始时效果很好。但随后相机开始不按预期旋转。如何使用滚动使相机相对于场景（对象）的中心正确移动？也许有人解决了类似的问题？

感谢您的任何回答/评论！

解决办法：

  private float kx = 0f;
  private float ky = 0f;
  private float radius = 3.0f;
  private float x, y, z = 0f;

  ...
  public synchronized void setMotion(float xDistance, float yDistance) {
      kx = kx + xDistance * 0.001f;
      x = (float) (radius * Math.sin(kx));
      z = (float) (radius * Math.cos(kx));

      ky = ky + yDistance * 0.001f;
      y = (float) (radius * Math.sin(ky));

      Matrix.setLookAtM(viewMatrix, 0, x, -y, z, 0f, 0f, 0f, 0f, 1.0f, 0.0f);
  }

但是使用这种方法，相机在沿 Y 轴旋转时会远离场景。

Answer 1

在矩阵代数中，顺序很重要。由于增量旋转交错矩阵和中断顺序，它不会像您期望的那样工作。因此，您需要在每次 setMotion() 调用时根据累积 delta x/y 重建视图矩阵，以便始终以正确的顺序应用旋转，如下所示。

public class SceneRenderer implements GLSurfaceView.Renderer {
    private float[] viewMatrix = new float[16];
    private float cumulativeX = 0.0f;
    private float cumulativeY = 0.0f;

    @Override
    public void onSurfaceCreated(GL10 gl, EGLConfig config) {
        Matrix.setLookAtM(viewMatrix, 0, 0f, 0f, 3f,
        0f, 0f, 0f, 0f, 1.0f, 0.0f);
        cumulativeX = 0.0f;
        cumulativeY = 0.0f;
    }

    ...
    // movement of camera
    public synchronized void setMotion(float xDistance, float yDistance) {

        cumulativeX += xDistance;
        cumulativeY += yDistance;

        Matrix.setLookAtM(viewMatrix, 0, 0f, 0f, 3f,
            0f, 0f, 0f, 0f, 1.0f, 0.0f);

        //Matrix.rotateM(viewMatrix, 0, -cumulativeX * 0.1f, 0, 1, 0);
        //Matrix.rotateM(viewMatrix, 0, -cumulativeY * 0.1f, 1, 0, 0);

        Matrix.rotateM(viewMatrix, 0, -cumulativeY * 0.1f, 1, 0, 0);
        Matrix.rotateM(viewMatrix, 0, -cumulativeX * 0.1f, 0, 1, 0);
    }
}

附录：仅通过 setLookAtM 组合视图矩阵

当然只有使用 setLookAtM 才能达到同样的效果。要使视点保持恒定距离，请在spherical coordinates 中移动视点。并向上调整。

public synchronized void setMotion(float xDistance, float yDistance) {

    kx = kx + xDistance * 0.001f;
    ky = ky + yDistance * 0.001f;
    
    x = (float) (radius * Math.cos(ky) * Math.sin(kx));
    z = (float) (radius * Math.cos(ky) * Math.cos(kx));
    y = (float) (radius * Math.sin(ky));


    float[] up =
    {
        (float) (Math.sin(ky) * Math.sin(kx)),
        (float) (Math.cos(ky)),
        (float) (Math.sin(ky) * Math.cos(kx)),
    };
    Matrix.setLookAtM(viewMatrix, 0,
            x, -y, z,
            0f, 0f, 0f,
            up[0], up[1], up[2]
    );

}