使用glDrawArrays繪製OpenGL ES的立方體

以前，我一直在使用glDrawElements繪製一些3D形狀，但是當涉及到以不同方式着色面部時，事實證明最好擁有唯一的頂點。使用glDrawArrays繪製OpenGL ES的立方體

我一直在試圖重寫我以前工作的多維數據集類，以使用glDrawArrays來代替併爲每個頂點提供顏色（和正常但我沒有使用它）數據，但現在我無法在屏幕上看到任何東西。流程非常多：編譯着色器，創建程序和附加着色器，爲模型數據創建緩衝區，設置程序，傳遞指向模型數據的指針，傳遞MVP矩陣，繪製。

我認爲我已經完成了我爲glDrawElements所做的等價事情，所以我認爲我會責怪我的着色器代碼，但是我真的不清楚什麼是錯的。任何幫助讚賞。

public class Cube { 

private final String vertexShaderCode = 
     "uniform mat4 uMVPMatrix;" + 
     "attribute vec4 aPosition;" + 
     "attribute vec4 aColor; \n" 
     + "attribute vec3 aNormal; \n" 
     + "varying vec4 v_Color; \n"  
     + "void main() {" + 
     " gl_Position = uMVPMatrix * vPosition;" + 
     "}"; 

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

// Store our data in float buffer. 
private final FloatBuffer mCubePositions; 
private final FloatBuffer mCubeColors; 
private final FloatBuffer mCubeNormals; 

// Bytes per float. 
private final int mBytesPerFloat = 4; 

/** Size of the position data in elements. */ 
private final int mPositionDataSize = 3;  
/** Size of the color data in elements. */ 
private final int mColorDataSize = 4; 
/** Size of the normal data in elements. */ 
private final int mNormalDataSize = 3; 

private final int mProgram; 
private int mPositionHandle; 
private int mColorHandle; 
private int mNormalHandle; 
private int mMVPMatrixHandle; 

final float[] cubePositionData = 
    {... 
    }; 

    final float[] cubeColorData = 
    {... 
    }; 

    final float[] cubeNormalData = 
    {... 
    }; 

/** 
* Sets up the drawing object data for use in an OpenGL ES context. 
*/ 
public Cube() { 
    // prepare shaders and OpenGL program 
    int vertexShader = MyGLRenderer.loadShader(
      GLES20.GL_VERTEX_SHADER, 
      vertexShaderCode); 
    int fragmentShader = MyGLRenderer.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);     // create OpenGL program executables 

    // Initialize the buffers. 
    mCubePositions = ByteBuffer.allocateDirect(cubePositionData.length * mBytesPerFloat) 
    .order(ByteOrder.nativeOrder()).asFloatBuffer();  
    mCubePositions.put(cubePositionData); 
    mCubePositions.position(0); 

    mCubeColors = ByteBuffer.allocateDirect(cubeColorData.length * mBytesPerFloat) 
    .order(ByteOrder.nativeOrder()).asFloatBuffer();  
    mCubeColors.put(cubeColorData); 
    mCubeColors.position(0); 

    mCubeNormals = ByteBuffer.allocateDirect(cubeNormalData.length * mBytesPerFloat) 
    .order(ByteOrder.nativeOrder()).asFloatBuffer();  
    mCubeNormals.put(cubeNormalData); 
    mCubeNormals.position(0); 
} 

public void draw(float[] mMVPMatrix) { 
    // Add program to OpenGL environment 
    GLES20.glUseProgram(mProgram); 

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

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

    mNormalHandle = GLES20.glGetAttribLocation(mProgram, "aNormal"); 

    // get handle to shape's transformation matrix 
    mMVPMatrixHandle = GLES20.glGetUniformLocation(mProgram, "uMVPMatrix"); 

    // Apply the projection and view transformation 
    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0); 

    // Pass in the position information 
    mCubePositions.position(0); 
    GLES20.glVertexAttribPointer(mPositionHandle, mPositionDataSize, 
      GLES20.GL_FLOAT, false, 0, mCubePositions); 
    GLES20.glEnableVertexAttribArray(mPositionHandle); 

    // Pass in the color information 
    mCubeColors.position(0); 
    GLES20.glVertexAttribPointer(mColorHandle, mColorDataSize, 
      GLES20.GL_FLOAT, false, 0, mCubeColors); 
    GLES20.glEnableVertexAttribArray(mColorHandle); 

    // Pass in the normal information 
    mCubeNormals.position(0); 
    GLES20.glVertexAttribPointer(mNormalHandle, mNormalDataSize, 
      GLES20.GL_FLOAT, false, 0, mCubeNormals); 
    GLES20.glEnableVertexAttribArray(mNormalHandle); 

    // Pass in the combined matrix. 
    GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mMVPMatrix, 0); 

    // Draw the cube. 
    GLES20.glDrawArrays(GLES20.GL_TRIANGLES, 0, 36); 

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

來源

2014-09-18 TheLastBert

你的頂點着色器代碼偏出分配一個值到v_Color不同變量，這導致沒有顏色被傳遞從頂點着色器到片段着色器。你需要在這個頂點着色器代碼添加到main()功能：

v_Color = aColor;

還有是不匹配的名字aPosition聲明之間，然後使用名爲vPosition一（不確定）變量。

我強烈建議您檢查着色器編譯的結果，並在失敗時研究錯誤。 glGetShaderiv()和glGetShaderInfoLog()是你的朋友。

來源

2014-09-19 05:33:36

使用glDrawArrays繪製OpenGL ES的立方體

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