Android GLES 2画线闪烁和奇怪的效果

Question

我正在尝试使用 gles 2 在 android 中绘制一些 3d 线。但它导致了一些奇怪的效果。当我旋转场景/相机时会发生闪烁。但不仅如此，还有一些随机绘制的 2d 线(有时是点)。这是屏幕截图:

虽然这张图片完全没有问题(使用不同的相机角度):

我也尝试过使用 GLES 1 来绘制这些线条并且它起作用了(没有闪烁或随机线条)。也许它与着色器代码有关？顶点着色器取自 android gles 示例，非常简单。

更新:经过更多尝试，我发现只有当相机偏航(y 轴旋转)超过 90 度时才会发生这种情况。在 0-90 yaw 范围内，线条显示正常。我究竟做错了什么？我正在使用 android v4.4.2 在 Galaxy Tab S 上运行该程序。

下面是用于重现错误图像的完整代码:

主要 Activity :

package com.mycompany.bug_test;

import android.opengl.GLSurfaceView;
import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;

public class OpenGLES20Activity extends ActionBarActivity {

    private GLSurfaceView mGLView = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        if ( mGLView == null ) {
            mGLView = new MyGLSurfaceView(this);
        }
        setContentView(mGLView);
    }
}

表面 View :

package com.mycompany.bug_test;

import android.content.Context;
import android.opengl.GLSurfaceView;
import android.view.MotionEvent;

class MyGLSurfaceView extends GLSurfaceView {

    private final MyGLRenderer mRenderer;

    public MyGLSurfaceView(Context context) {
        super(context);

        setEGLContextClientVersion(2);

        mRenderer = new MyGLRenderer();
        setRenderer(mRenderer);
    }

    private final float TOUCH_SCALE_FACTOR = 360.0f;
    private float mPreviousX;
    private float mPreviousY;

    @Override
    public boolean onTouchEvent(MotionEvent e) {

        float x = e.getX();
        float y = e.getY();

        int action_type = e.getAction();
        if ( action_type ==  MotionEvent.ACTION_MOVE ) {
            float dx = x - mPreviousX;
            float dy = y - mPreviousY;

            final float div_mag = 10;
            float min_dx = dx;
            if ( min_dx > (getRootView().getWidth()/div_mag) ) {min_dx = (getRootView().getWidth()/div_mag);}
            if ( min_dx < -(getRootView().getWidth()/div_mag) ) {min_dx = -(getRootView().getWidth()/div_mag);}
            float min_dy = dy;
            if ( min_dy > (getRootView().getHeight()/div_mag) ) {min_dy = (getRootView().getHeight()/div_mag);}
            if ( min_dy < -(getRootView().getHeight()/div_mag) ) {min_dy = -(getRootView().getHeight()/div_mag);}

            float new_yaw = (  mRenderer.cam_yaw - (min_dx * TOUCH_SCALE_FACTOR / getRootView().getWidth())  ) % 360;
            float new_pitch = mRenderer.cam_pitch + (min_dy * TOUCH_SCALE_FACTOR / getRootView().getHeight());
            if ( new_pitch > 89 ) {
                new_pitch = 89;
            }
            if ( new_pitch < -89 ) {
                new_pitch = -89;
            }


            synchronized (mRenderer.CAM_LOCK) {
                mRenderer.cam_yaw = new_yaw;
                mRenderer.cam_pitch = new_pitch;
            }
            System.out.println("Yaw=" + new_yaw + "   Pitch=" + new_pitch);
        }

        mPreviousX = x;
        mPreviousY = y;
        return true;
    }
}

还有最重要的部分，GL渲染器:

package com.mycompany.bug_test;

import android.opengl.GLES20;
import android.opengl.GLSurfaceView;
import android.opengl.Matrix;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import java.nio.FloatBuffer;

import javax.microedition.khronos.egl.EGLConfig;
import javax.microedition.khronos.opengles.GL10;

public class MyGLRenderer implements GLSurfaceView.Renderer {

    private final String vertexShaderCode =
            "uniform mat4 uMVPMatrix;" +
            "attribute vec4 vPosition;" +
            "void main() {" +
            "   gl_Position = uMVPMatrix * vPosition;" +
            "}";

    private final String fragmentShaderCode =
            "precision mediump float;" +
            "uniform vec4 vColor;" +
            "void main() {" +
            "   gl_FragColor = vColor;" +
            "}";

    private int mProgram;

    private int mMVPMatrixHandle;
    private int mPositionHandle;
    private int mColorHandle;



    private final float[] mProjectionMatrix = new float[16];
    private final float[] mViewMatrix = new float[16];
    float viewAspect;
    float fovy = 45;
    float fovx = 45;

    final Object CAM_LOCK = new Object();
    float cam_pos_x = 0;
    float cam_pos_y = 0;
    float cam_pos_z = 0;
    float fcs_pos_x = 0;
    float fcs_pos_y = 0;
    float fcs_pos_z = 0;
    //Try Yaw=246.22672   Pitch=21.992342 with cam_focus_range = 175 to get visible error.
    float cam_pitch = 21.992342f;
    float cam_yaw = 246.22672f;
    float cam_focus_range = 175;



    final float line_gap = 100;
    final float line_length = 6000;

    private final int COORDS_PER_VERTEX = 3;
    private final int vertexStride = COORDS_PER_VERTEX * 4; // 4 bytes per vertex

    private FloatBuffer vertexBuffer;
    private int vertexCount = 0;


    public MyGLRenderer() {
        float[] GMrkLines = new float[(int)( (line_length / line_gap) + 1 ) * 2 * 2 * COORDS_PER_VERTEX ];

        int __P = 0;
        for (int ln=0; ln<( (line_length / line_gap) + 1 ); ln++) {
            GMrkLines[__P++] = (float)(line_length /2);                             //x
            GMrkLines[__P++] = 0;                                                   //y
            GMrkLines[__P++] = (float)(line_gap *ln - line_length /2);              //z
            vertexCount++;
            GMrkLines[__P++] = (float)(-line_length /2);                            //x
            GMrkLines[__P++] = 0;                                                   //y
            GMrkLines[__P++] = (float)(line_gap *ln - line_length /2);              //z
            vertexCount++;

            GMrkLines[__P++] = (float)(line_gap *ln - line_length /2);              //x
            GMrkLines[__P++] = 0;                                                   //y
            GMrkLines[__P++] = (float)(line_length /2);                             //z
            vertexCount++;
            GMrkLines[__P++] = (float)(line_gap *ln - line_length /2);              //x
            GMrkLines[__P++] = 0;                                                   //y
            GMrkLines[__P++] = (float)(-line_length /2);                            //z
            vertexCount++;
        }

        System.out.println("Vertex count=" + vertexCount);

        {
            ByteBuffer bb = ByteBuffer.allocateDirect(GMrkLines.length * 4);
            bb.order(ByteOrder.nativeOrder());
            vertexBuffer = bb.asFloatBuffer();
            vertexBuffer.put(GMrkLines);
            vertexBuffer.position(0);
        }
    }


    @Override
    public void onSurfaceCreated(GL10 unused, EGLConfig config) {
        int vertexShader = MyGLRenderer.loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode);
        int fragmentShader = MyGLRenderer.loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode);
        mProgram = GLES20.glCreateProgram();

        GLES20.glAttachShader(mProgram, vertexShader);
        GLES20.glAttachShader(mProgram, fragmentShader);
        GLES20.glLinkProgram(mProgram);

        GLES20.glUseProgram(mProgram);

        mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix");
        mPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition");
        mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor");

        GLES20.glUniform4fv(mColorHandle, 1, new float[]{0.3f, 0.3f, 0.3f, 1}, 0);


        GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f);
        GLES20.glEnable( GLES20.GL_DEPTH_TEST );
        GLES20.glDepthFunc( GLES20.GL_LEQUAL );
        GLES20.glLineWidth(4);
    }

    @Override
    public void onDrawFrame(GL10 unused) {
        float _cam_pos_x;
        float _cam_pos_y;
        float _cam_pos_z;
        float _fcs_pos_x;
        float _fcs_pos_y;
        float _fcs_pos_z;
        float _cam_pitch;
        float _cam_yaw;
        synchronized (CAM_LOCK) {
            _cam_pos_x = cam_pos_x;
            _cam_pos_y = cam_pos_y;
            _cam_pos_z = cam_pos_z;
            _fcs_pos_x = fcs_pos_x;
            _fcs_pos_y = fcs_pos_y;
            _fcs_pos_z = fcs_pos_z;
            _cam_pitch = cam_pitch;
            _cam_yaw = cam_yaw;
        }


        GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT);


        _fcs_pos_x = 0;
        _fcs_pos_y = 0;
        _fcs_pos_z = 0;
        _cam_pos_y = (float) ( _fcs_pos_y + (cam_focus_range * Math.sin( Math.toRadians(_cam_pitch) )));
        double cam_to_focus_horz = cam_focus_range * Math.cos( Math.toRadians(_cam_pitch) );
        _cam_pos_x = (float) ( _fcs_pos_x + (cam_to_focus_horz * Math.cos( Math.toRadians(_cam_yaw) )));
        _cam_pos_z = (float) ( _fcs_pos_z + (cam_to_focus_horz * Math.sin( Math.toRadians(_cam_yaw) )));

        Matrix.setLookAtM(mViewMatrix, 0, _cam_pos_x, _cam_pos_y,_cam_pos_z, _fcs_pos_x, _fcs_pos_y, _fcs_pos_z, 0, 1, 0);


        {
            float[] mMVPMatrix = new float[16];
            Matrix.multiplyMM(mMVPMatrix, 0, mProjectionMatrix, 0, mViewMatrix, 0);
            GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0);

            GLES20.glEnableVertexAttribArray(mPositionHandle);

            GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, GLES20.GL_FLOAT, false,
                    vertexStride, vertexBuffer);
            GLES20.glDrawArrays(GLES20.GL_LINES, 0, vertexCount);

            GLES20.glDisableVertexAttribArray(mPositionHandle);
        }
    }

    @Override
    public void onSurfaceChanged(GL10 unused, int width, int height) {
        if (height <= 0) { // avoid a divide by zero error!
            height = 1;
        }
        viewAspect = (float) width / (float) height;
        fovx = fovy * viewAspect;

        GLES20.glViewport(0, 0, width, height);
        GLU_perspective(mProjectionMatrix, 0, fovy, viewAspect, 1.0f, 8000.0f);
    }


    public static int loadShader(int type, String shaderCode) {
        int shader = GLES20.glCreateShader(type);

        GLES20.glShaderSource(shader, shaderCode);
        GLES20.glCompileShader(shader);

        int[] _param = new int[4];
        GLES20.glGetShaderiv(shader, GLES20.GL_COMPILE_STATUS, _param, 0);
        System.out.println("Shader no : " + shader);
        System.out.println("Compile status = " + _param[0] + "   (GL_TRUE=" + GLES20.GL_TRUE + ")");
        System.out.println("ERR : " + GLES20.glGetShaderInfoLog(shader));

        return shader;
    }

    void GLU_perspective(float[] RetMtx, int offset, float fovY, float aspect, float zNear, float zFar)
    {
        float fW, fH;

        fH = (float) (Math.tan(fovY / 360 * Math.PI) * zNear);
        fW = fH * aspect;

        Matrix.frustumM(RetMtx, offset, -fW, fW, -fH, fH, zNear, zFar );
    }
}

Answer 1

我遇到了同样的问题，尤其是三星设备(我有 3 台三星设备出现了同样的问题)。事实证明，使用 GL_LINE_STRIP 或 GL_LINES 绘制线条会导致您在屏幕截图中显示的伪影和闪烁。但前提是直线穿过相机平面，并且直线的第一个坐标在相机平面后面，第二个坐标在相机平面前面。反过来 - 没问题。

在我看来，这根本没有意义，因此似乎是驱动程序问题 - 您的代码中没有错误。

作为解决方法，我让顶点着色器检测这个星座，然后翻转顶点。检测是通过检查矩阵的 z 缩放分量 [2][2] 的符号来完成的。在我的例子中，顶点是 {0,0,1} 和 {0,0,-1} - 因此可以通过取反顶点值轻松完成翻转。

// Vertex shader snippet
cPosition = vPosition;
voMatrix = viewMatrix * objMatrix;
if ( voMatrix [2][2] < 0.0 ) cPosition = -vPosition;

我希望这会有所帮助(即使答案来得很晚)。