生成球體時的空指針

Question

我試圖在opengl es 2.0中創建一個球體，但我得到一個空指針異常。我一直堅持這幾個小時。在檢查logcat後，它似乎找到了幾個頂點，但是索引緩衝區總是直接擊中空指針。

private void generateSphereCoords(float radius, int stacks, int slices) { 
    for (int stackNumber = 0; stackNumber <= stacks; stackNumber++) { 
     for (int sliceNumber = 0; sliceNumber <= slices; sliceNumber++) { 
      float theta = (float) (stackNumber * Math.PI/stacks); 
      float phi = (float) (sliceNumber * 2 * Math.PI/slices); 
      Log.i("theta", String.valueOf(theta)); 
      Log.i("phi", String.valueOf(phi)); 
      float sinTheta = FloatMath.sin(theta); 
      float sinPhi = FloatMath.sin(phi); 
      float cosTheta = FloatMath.cos(theta); 
      float cosPhi = FloatMath.cos(phi); 
      vertices = new float[]{radius * cosPhi * cosTheta, radius * sinPhi * cosTheta, radius * sinTheta}; 
      Log.i("vertexX", String.valueOf(vertices[0])); 
      Log.i("vertexY", String.valueOf(vertices[1])); 
      Log.i("vertexZ", String.valueOf(vertices[2])); 
      // a float is 4 bytes, therefore I multiply the number of vertices by 4. 
      ByteBuffer vbb = ByteBuffer.allocateDirect(vertices.length * 4);// (number of coordinate values * 4 bytes per float) 
      vbb.order(ByteOrder.nativeOrder());// use the device hardware's native byte order 
      vertexBuffer = vbb.asFloatBuffer();// create a floating point buffer from the ByteBuffer 
      vertexBuffer.put(vertices); 
      vertexBuffer.position(0);// set the buffer to read the first coordinate 
     } 
    } 

    for (int stackNumber = 0; stackNumber <= stacks; stackNumber++) { 
     for (int sliceNumber = 0; sliceNumber <= slices; sliceNumber++) { 
      ByteBuffer ibb = ByteBuffer.allocateDirect(vertexCount * 2);// (number of coordinate values * 4 bytes per float) 
      ibb.order(ByteOrder.nativeOrder());// use the device hardware's native byte order 
      indexBuffer = ibb.asShortBuffer();// create a floating point buffer from the ByteBuffer 
      indexBuffer.put((short) ((stackNumber * slices) + (sliceNumber % slices))); 
      indexBuffer.put((short) (((stackNumber + 1) * slices) + (sliceNumber % slices))); 
      indexBuffer.position(0);// set the buffer to read the first coordinate 
     } 
    } 
} 

Answer 1

在循環之外創建頂點緩衝區和索引緩衝區。因爲您正在重新創建每個頂點的頂點緩衝區以及每對索引的索引緩衝區。

private static final int VERTICES_PER_COORD = 3; 
private void generateSphereCoords(float radius, int stacks, int slices) { 

    // Create vertex buffer here: 
    ByteBuffer vbb = ByteBuffer.allocateDirect((stacks + 1) * (slices + 1) * VERTICES_PER_COORD * 4);// (number of coordinate values * 4 bytes per float) 
    vbb.order(ByteOrder.nativeOrder());// use the device hardware's native byte order 
    vertexBuffer = vbb.asFloatBuffer();// create a floating point buffer from the ByteBuffer 

    for (int stackNumber = 0; stackNumber <= stacks; stackNumber++) { 
     for (int sliceNumber = 0; sliceNumber <= slices; sliceNumber++) { 
      float theta = (float) (stackNumber * Math.PI/stacks); 
      float phi = (float) (sliceNumber * 2 * Math.PI/slices); 
      Log.i("theta", String.valueOf(theta)); 
      Log.i("phi", String.valueOf(phi)); 
      float sinTheta = FloatMath.sin(theta); 
      float sinPhi = FloatMath.sin(phi); 
      float cosTheta = FloatMath.cos(theta); 
      float cosPhi = FloatMath.cos(phi); 
      vertices = new float[]{radius * cosPhi * cosTheta, radius * sinPhi * cosTheta, radius * sinTheta}; 
      Log.i("vertexX", String.valueOf(vertices[0])); 
      Log.i("vertexY", String.valueOf(vertices[1])); 
      Log.i("vertexZ", String.valueOf(vertices[2])); 
      // a float is 4 bytes, therefore I multiply the number of vertices by 4. 

      // add this vertex tp the buffer:   
      vertexBuffer.put(vertices);     
     } 
    } 
    vertexBuffer.position(0);// set the buffer to read the first coordinate 

    // Create index buffer here: 
    ByteBuffer ibb = ByteBuffer.allocateDirect((stacks + 1) * (slices + 1) * 2 * 2);// (number of index values * 2 bytes per short) 
    ibb.order(ByteOrder.nativeOrder());// use the device hardware's native byte order 
    indexBuffer = ibb.asShortBuffer();// create a floating point buffer from the ByteBuffer 

    for (int stackNumber = 0; stackNumber <= stacks; stackNumber++) { 
     for (int sliceNumber = 0; sliceNumber <= slices; sliceNumber++) {     
      indexBuffer.put((short) ((stackNumber * slices) + (sliceNumber % slices))); 
      indexBuffer.put((short) (((stackNumber + 1) * slices) + (sliceNumber % slices)));     
     } 
    } 
    indexBuffer.position(0);// set the buffer to read the first index 
}