不能在OpenGL ES 2.0上繪製一個三角形android

Question

我正在編寫與developer.android.com關於使用opengl的教程，因爲我遇到了一些錯誤，我試圖修復它們，但它沒有解決。我創建了主要活動，當您按下按鈕時，意圖打開一個顯示黑色屏幕但不顯示三角形的opengl活動。你能告訴我問題在哪裏嗎？

這是我的MainActivity類別：

package com.eBook.test; 

import android.content.Intent; 
import android.os.Bundle; 
import android.support.v4.app.Fragment; 
import android.support.v7.app.ActionBarActivity; 
import android.view.LayoutInflater; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.view.ViewGroup; 
import android.widget.Button; 

public class MainActivity extends ActionBarActivity { 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_main); 

    final Button button = (Button)findViewById(R.id.button); 
    button.setOnClickListener(new OnClickListener() { 
     public void onClick(View v){ 
      Intent intent = new Intent (MainActivity.this, OpenGLES20Activity.class);        
      startActivity(intent); 
     } 
    }); 


} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 

    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.main, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 
    if (id == R.id.action_settings) { 
     return true; 
    } 
    return super.onOptionsItemSelected(item); 
} 

/** 
* A placeholder fragment containing a simple view. 
*/ 
public static class PlaceholderFragment extends Fragment { 

    public PlaceholderFragment() { 
    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
      Bundle savedInstanceState) { 
     View rootView = inflater.inflate(R.layout.fragment_main, container, 
       false); 
     return rootView; 
    } 
} 

} 

一切似乎確定這一點，現在這裏是我的OpenGL活動類：

package com.eBook.test; 

import android.app.Activity; 
import android.content.Context; 
import android.opengl.GLSurfaceView; 
import android.os.Bundle; 

public class OpenGLES20Activity extends Activity { 

private GLSurfaceView mGLView; 

class MyGLSurfaceView extends GLSurfaceView { 

    public MyGLSurfaceView(Context context){ 
     super(context); 
    // Create an OpenGL ES 2.0 context 
     setEGLContextClientVersion(2); 

     // Set the Renderer for drawing on the GLSurfaceView 
     setRenderer(new MyRenderer()); 
     setRenderMode(GLSurfaceView.RENDERMODE_WHEN_DIRTY); 

    } 
} 

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

    // Create a GLSurfaceView instance and set it 
    // as the ContentView for this Activity. 
    mGLView = new MyGLSurfaceView(this); 
    setContentView(mGLView); 



} 

@Override 
protected void onPause() { 
    mGLView.onPause(); 
    super.onPause(); 
} 

@Override 
protected void onResume() { 
    mGLView.onResume(); 
    super.onResume(); 
} 


} 

這是我的渲染器類：

package com.eBook.test; 

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

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

public class MyRenderer implements GLSurfaceView.Renderer { 

private Triangle mTriangle; 


public void onSurfaceCreated(GL10 unused, EGLConfig config) { 
    // Set the background frame color 
    GLES20.glClearColor(0.0f, 0.0f, 0.0f, 1.0f); 
// initialize a triangle 
    mTriangle = new Triangle(); 

} 


public void onDrawFrame(GL10 unused) { 
    // Redraw background color 

    mTriangle.draw(); 
    GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); 

} 

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

public static 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; 
} 

} 

和三角類：

package com.eBook.test; 

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

import android.opengl.GLES20; 

public class Triangle { 

private FloatBuffer vertexBuffer; 
private int mProgram; 
private int mPositionHandle; 
private int mColorHandle; 


// number of coordinates per vertex in this array 
static final int COORDS_PER_VERTEX = 3; 
static float triangleCoords[] = { // in counterclockwise order: 
     0.0f, 0.622008459f, 0.0f, // top 
     -0.5f, -0.311004243f, 0.0f, // bottom left 
     0.5f, -0.311004243f, 0.0f // bottom right 
}; 

// Set color with red, green, blue and alpha (opacity) values 
float color[] = { 0.63671875f, 0.76953125f, 0.22265625f, 1.0f }; 


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

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


public Triangle() { 



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

    mProgram = GLES20.glCreateProgram();    // create empty OpenGL ES 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 ES program executables 




    // initialize vertex byte buffer for shape coordinates 
    ByteBuffer bb = ByteBuffer.allocateDirect(
      // (number of coordinate values * 4 bytes per float) 
      triangleCoords.length * 4); 
    // use the device hardware's native byte order 
    bb.order(ByteOrder.nativeOrder()); 

    // create a floating point buffer from the ByteBuffer 
    vertexBuffer = bb.asFloatBuffer(); 
    // add the coordinates to the FloatBuffer 
    vertexBuffer.put(triangleCoords); 
    // set the buffer to read the first coordinate 
    vertexBuffer.position(0); 

} 

    public void draw() { 
     // Add program to OpenGL ES environment 
     GLES20.glUseProgram(mProgram); 

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

     // Enable a handle to the triangle vertices 
     GLES20.glEnableVertexAttribArray(mPositionHandle); 

     // Prepare the triangle coordinate data 

     int vertexStride = 3; 
     GLES20.glVertexAttribPointer(mPositionHandle, COORDS_PER_VERTEX, 
            GLES20.GL_FLOAT, false, 
            vertexStride, vertexBuffer); 

     // get handle to fragment shader's vColor member 
     mColorHandle = GLES20.glGetUniformLocation(mProgram, "vColor"); 

     // Set color for drawing the triangle 
     GLES20.glUniform4fv(mColorHandle, 1, color, 0); 

     // Draw the triangle 


     int vertexCount = 6; 
     GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, vertexCount); 

     // Disable vertex array 
     GLES20.glDisableVertexAttribArray(mPositionHandle); 
    } 



} 

我真的不知道vertexCount和vertexStride應該保持什麼值，邏輯上認爲vertexCount應該是3，也許不知道vertexStride。

Answer 1

清除繪製三角形前的背景;）

public void onDrawFrame(GL10 unused) { 
// Redraw background color 

GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GL10.GL_DEPTH_BUFFER_BIT); 
mTriangle.draw(); 

}