返回NullPointerException的GLu.gluUnProject

Question

我将gluUnProject设置为在触摸上查找世界坐标，如下所示：

public synchronized void randomMethod(MotionEvent event){
        if (event.getAction() == MotionEvent.ACTION_DOWN){
        setx = event.getX();
        sety = event.getY();
        vector3(null);
        }
    }

    public void vector3 (GL11 gl){

        int[] viewport = new int[4];
        float[] modelview = new float[16];
        float[] projection = new float[16];
        float winx, winy, winz;
        float[] newcoords = new float[3];

        gl.glGetIntegerv(GL11.GL_VIEWPORT, viewport, 0);
        gl.glGetFloatv(GL11.GL_MODELVIEW_MATRIX, modelview, 0);
        gl.glGetFloatv(GL11.GL_PROJECTION_MATRIX, projection, 0);

        winx = (float)setx;
        winy = (float)viewport[3] - sety;
        winz = 0;

        GLU.gluUnProject(winx, winy, winz, modelview, 0, projection, 0, viewport, 0, newcoords, 0);
        posx = (int)newcoords[1];
        posy = (int)newcoords[2];
        posz = (int)newcoords[3];


    }

然后在draw方法中使用新坐标在接触点绘制一个正方形。

但是，这段代码返回一个NullPointerException。

07-31 20:17:40.008: ERROR/AndroidRuntime(448): Uncaught handler: thread main exiting due to uncaught exception
07-31 20:17:40.098: ERROR/AndroidRuntime(448): java.lang.NullPointerException
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.app.ui.GLSurfaceRenderer.vector3(GLSurfaceRenderer.java:65)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.app.ui.GLSurfaceRenderer.randomMethod(GLSurfaceRenderer.java:54)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.app.ui.Practice.onTouchEvent(Practice.java:37)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.app.Activity.dispatchTouchEvent(Activity.java:2064)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchTouchEvent(PhoneWindow.java:1643)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.view.ViewRoot.handleMessage(ViewRoot.java:1690)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.os.Handler.dispatchMessage(Handler.java:99)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.os.Looper.loop(Looper.java:123)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at android.app.ActivityThread.main(ActivityThread.java:4310)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at java.lang.reflect.Method.invokeNative(Native Method)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at java.lang.reflect.Method.invoke(Method.java:521)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:860)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:618)
07-31 20:17:40.098: ERROR/AndroidRuntime(448):     at dalvik.system.NativeStart.main(Native Method)

第54行是

vector3(null);

第65行是

gl.glGetIntegerv(GL11.GL_VIEWPORT, viewport, 0);

练习课的第37行是

glSurfaceRenderer.randomMethod(event);

它在randomMethod被同步到的touchEvent内部调用。

有人知道是什么导致空指针异常吗？

谢谢

Answer 1

GLU.gluUnProject似乎与你得到的NullPointerException无关。

您正在呼叫：

vector3(null);

因此，在函数vector3(GL11 Gl)中：

gl.glGetIntegerv(GL11.GL_VIEWPORT, viewport, 0);

因为gl为空而引发NPE。

您需要初始化GL11实现，即：

OpenGLContext glContext = new OpenGLContext(OpenGLContext.DEPTH_BUFFER);
GL11 gl = (GL11)glContext.getGL();