在Open ES iPhone应用程序中围绕VBO使用VAO导致调用glDrawElements时出现EXC_BAD_ACCESS

Question

我正在尝试将我的代码提升到一个新的水平.遵循Apple的一些最佳实践,我试图在我的顶点缓冲对象(VBO)周围实现顶点数组对象.我设置我的VBO和VAO像这样:

- (void)setupVBOs {  
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindVertexArrayOES(0);
    {
        glGenVertexArraysOES(1, &directArrayObject);
        glBindVertexArrayOES(directArrayObject);

    //    GLuint texCoordBuffer;
        glGenBuffers(1, &texCoordBuffer);
        glBindBuffer(GL_ARRAY_BUFFER, texCoordBuffer);
        glBufferData(GL_ARRAY_BUFFER, sizeof(DirectVertices), DirectVertices, GL_STATIC_DRAW);

        glVertexAttribPointer(directPositionSlot, 2, GL_FLOAT, GL_FALSE, sizeof(DirectVertex), (GLvoid*)offsetof(DirectVertex, position));
        glEnableVertexAttribArray(directPositionSlot);
        glVertexAttribPointer(texCoordSlot, 2, GL_UNSIGNED_BYTE, GL_FALSE, sizeof(DirectVertex), (GLvoid*)offsetof(DirectVertex, texCoord));
        glEnableVertexAttribArray(texCoordSlot);

        glGenVertexArraysOES(1, &arrayObject);
        glBindVertexArrayOES(arrayObject);

    //    GLuint vertexBuffer;
        glGenBuffers(1, &vertexBuffer);
        glBindBuffer(GL_ARRAY_BUFFER, vertexBuffer);
        glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);

        glVertexAttribPointer(positionSlot, 3, GL_FLOAT, GL_FALSE, sizeof(Vertex), 0);
        glEnableVertexAttribArray(positionSlot);
        glVertexAttribPointer(colorSlot, 4, GL_UNSIGNED_BYTE, GL_FALSE, sizeof(Vertex), (GLvoid*)offsetof(Vertex, Color));
        glEnableVertexAttribArray(colorSlot);

    //    GLuint indexBuffer;
        glGenBuffers(1, &indexBuffer);
        glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexBuffer);
        glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(Indices), Indices, GL_STATIC_DRAW);
    }
    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
    glBindVertexArrayOES(0);
}

我从http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=287977获取,然后像这样使用它:

- (void) render:(CADisplayLink*)displayLink {

    glClearColor(0, 104.0/255.0, 55.0/255.0, 1.0);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glViewport(0, 0, backingWidth, backingHeight);

    [directProgram use];
    glBindVertexArrayOES(directArrayObject);
    glDisable(GL_DEPTH_TEST);

    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, videoFrameTexture);

//  // Update uniform values
    glUniform1i(videoFrameUniform, 0);

    glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

    [program use];
    glBindVertexArrayOES(arrayObject);
    glDisable(GL_TEXTURE_2D);
    glEnable(GL_DEPTH_TEST);

    CC3GLMatrix *projection = [CC3GLMatrix matrix];
    float h = 4.0f * self.frame.size.height / self.frame.size.width;
    [projection populateFromFrustumLeft:-2 andRight:2 andBottom:-h/2 andTop:h/2 andNear:4 andFar:10];
    glUniformMatrix4fv(projectionUniform, 1, 0, projection.glMatrix);

    CC3GLMatrix *modelView = [CC3GLMatrix matrix];
    [modelView populateFromTranslation:CC3VectorMake(sin(CACurrentMediaTime()), 0, -7)];
    currentRotation += displayLink.duration * 90;
    [modelView rotateBy:CC3VectorMake(currentRotation, currentRotation, 0)];
    glUniformMatrix4fv(modelViewUniform, 1, 0, modelView.glMatrix);

    glDrawElements(GL_TRIANGLES, sizeof(Indices)/sizeof(Indices[0]), GL_UNSIGNED_BYTE, 0);

    glBindVertexArrayOES(0);

    BOOL success = [context presentRenderbuffer:GL_RENDERBUFFER];
    if(!success)
        NSLog(@"present failed");
}

对glDrawArrays的调用有效,它填充了我的纹理,然而,对glDrawElements的调用因EXC_BAD_ACCESS而失败.我的着色器程序(我使用两个)包含在我从http://iphonedevelopment.blogspot.com/2010/11/opengl-es-20-for-ios-chapter-4.html获取的GLProgram对象中.

Answer 1

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);从设置功能的末尾删除.

根据规范OES_vertex_array_object,顶点数组对象封装除数组缓冲区绑定¹ 之外的所有状态,因此在绘制时没有绑定元素缓冲区,而您可能想要indexBuffer绑定.通过indexBuffer在绑定远离顶点数组对象时保留绑定,可以确保在返回到顶点数组对象时它会被反弹.

¹如果您想知道为什么在顶点数组对象中没有跟踪数组缓冲区绑定,这可能是因为当从数组中读取顶点数据时不直接使用当前绑定的数组缓冲区 - 而是每个顶点属性都有自己的缓冲区绑定,通过在gl*Pointer调用函数时查看数组缓冲区绑定,由其各自的函数填充.