Android的OpenGL ES教程似乎不起作用

Question

我一直在關注Android上的OpenGL ES的教程http://developer.android.com/resources/tutorials/opengl/opengl-es20.html。我已經到了「應用投影和相機視圖」部分，但是我總是看到沒有三角形的空白屏幕，前面的部分工作得很好。我也試過把整個教程粘貼到我的代碼中，但得到了相同的結果。改變線：

gl_Position = uMVPMatrix * vPosition; 

到：

gl_Position = vPosition; 

將應用程序返回到所述第一部分（三角形延綿根據屏幕取向）。任何想法是什麼問題？這裏是我迄今爲止的代碼，以防萬一我錯過了某些東西：

public class GLTest20Renderer implements Renderer { 
    private final String vertexShaderCode = 
     // This matrix member variable provides a hook to manipulate 
     // the coordinates of the objects that use this vertex shader 
     "uniform mat4 uMVPMatrix; \n" + 

     "attribute vec4 vPosition; \n" + 
     "void main(){    \n" + 

     // the matrix must be included as a modifier of gl_Position 
     " gl_Position = uMVPMatrix * vPosition; \n" + 

     "} \n"; 

    private final String fragmentShaderCode = 
     "precision mediump float; \n" + 
     "void main(){    \n" + 
     " gl_FragColor = vec4 (0.63671875, 0.76953125, 0.22265625, 1.0); \n" + 
     "}       \n"; 


    private FloatBuffer triangleVB; 

    private int mProgram; 
    private int maPositionHandle; 

    private int muMVPMatrixHandle; 
    private float[] mMVPMatrix = new float[16]; 
    private float[] mMMatrix = new float[16]; 
    private float[] mVMatrix = new float[16]; 
    private float[] mProjMatrix = new float[16]; 

    public void onSurfaceCreated(GL10 unused, EGLConfig config) { 
     GLES20.glClearColor(0.5f, 0.5f, 0.5f, 1.0f); 

     initShapes(); 

     int vertexShader = loadShader(GLES20.GL_VERTEX_SHADER, vertexShaderCode); 
     int fragmentShader = loadShader(GLES20.GL_FRAGMENT_SHADER, fragmentShaderCode); 

     mProgram = GLES20.glCreateProgram();    // create empty OpenGL Program 
     GLES20.glAttachShader(mProgram, vertexShader); // add the vertex shader to program 
     GLES20.glAttachShader(mProgram, fragmentShader); // add the fragment shader to program 
     GLES20.glLinkProgram(mProgram);     // creates OpenGL program executables 

     // get handle to the vertex shader's vPosition member 
     maPositionHandle = GLES20.glGetAttribLocation(mProgram, "vPosition"); 
    } 

    public void onDrawFrame(GL10 unused) { 
     GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT); 

     // Add program to OpenGL environment 
     GLES20.glUseProgram(mProgram); 

     // Prepare the triangle data 
     GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false, 12, triangleVB); 
     GLES20.glEnableVertexAttribArray(maPositionHandle); 

     // Apply a ModelView Projection transformation 
     Matrix.multiplyMM(mMVPMatrix, 0, mProjMatrix, 0, mVMatrix, 0); 
     GLES20.glUniformMatrix4fv(muMVPMatrixHandle, 1, false, mMVPMatrix, 0); 

     // Draw the triangle 
     GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 3); 
    } 

    public void onSurfaceChanged(GL10 unused, int width, int height) { 
     GLES20.glViewport(0, 0, width, height); 

     float ratio = (float) width/height; 

     Matrix.frustumM(mProjMatrix, 0, -ratio, ratio, -1, 1, 3, 7); 

     muMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix"); 
     Matrix.setLookAtM(mVMatrix, 0, 0, 0, -3, 0f, 0f, 0f, 0f, 1.0f, 0.0f); 
    } 

    private void initShapes() { 
     float triangleCoords[] = { 
      // X, Y, Z 
      -0.5f, -0.25f, 0, 
      0.5f, -0.25f, 0, 
      0.0f, 0.559016994f, 0 
     }; 

     // initialize vertex Buffer for triangle 
     ByteBuffer vbb = ByteBuffer.allocateDirect(
       // (# of coordinate values * 4 bytes per float) 
       triangleCoords.length * 4); 
     vbb.order(ByteOrder.nativeOrder());// use the device hardware's native byte order 
     triangleVB = vbb.asFloatBuffer(); // create a floating point buffer from the ByteBuffer 
     triangleVB.put(triangleCoords); // add the coordinates to the FloatBuffer 
     triangleVB.position(0);   // set the buffer to read the first coordinate 
    } 

    private int loadShader(int type, String shaderCode) { 
     // create a vertex shader type (GLES20.GL_VERTEX_SHADER) 
     // or a fragment shader type (GLES20.GL_FRAGMENT_SHADER) 
     int shader = GLES20.glCreateShader(type); 

     // add the source code to the shader and compile it 
     GLES20.glShaderSource(shader, shaderCode); 
     GLES20.glCompileShader(shader); 

     return shader; 
    } 
} 

我在三星Galaxy S2上運行所有這些。

Answer 1

固定的，只是改變了近點的LOOKAT是在3：

Matrix.frustumM(mProjMatrix, 0, -ratio, ratio, -1, 1, 2, 7);