ios - OpenGLES2 iOS 顶点数组对象在 drawElements 上导致错误的访问错误

Question

今天下午，当我从使用 VBO 转向 VAO/VBO 时，我一直在努力说服我的 openGLES2.0 代码正确执行。基本上，我正在按照 Apple 关于 openGLES 的“专家”建议进行工作，并转向使用顶点数组对象是最重要的……

我已经查看了类似的问题和回复 here但这似乎对我没有帮助，除了再次向我保证其他人遇到了类似的问题:(

我的场景是我有大约 500 个矩形纹理在屏幕上移动。没有 VAO，代码一切正常，但是当我定义 USE_VAO(我的常量)时，它在第一次绘制元素调用时崩溃。我显然没有正确理解 VAO ...但我看不到我的方法有错误!

setupBeforeRender 方法在进入渲染循环之前作为设置的最后一部分被调用。

-(void) setupBeforeRender {

glClearColor(0.6, 0.6, 0.6, 1);
glViewport(0, 0, self.frame.size.width, self.frame.size.height);
glEnable(GL_DEPTH_TEST);

glUniform1i(_textureUniform, 0);
glActiveTexture(GL_TEXTURE0); 

glEnableVertexAttribArray(_positionSlot);
glEnableVertexAttribArray(_colorSlot);
glEnableVertexAttribArray(_texCoordSlot);


glGenBuffers(1, &_indexBuffer);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _indexBuffer);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(Indices), Indices, GL_STATIC_DRAW);

}

这是渲染方法

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

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// Model view matrix and projection code removed for clarity

GLsizei stride = sizeof(Vertex);
const GLvoid* colourOffset = (GLvoid *) sizeof(float[3]);
const GLvoid* textureOffset = (GLvoid *) sizeof(float[7]);

 for (my objectToDraw in objectToDrawArray)
 {

    if (objectToDraw.vertexBufferObject == 0)
    {

        #ifdef USE_VAO

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

        glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, stride, 0);
        glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, stride, colourOffset);
        glVertexAttribPointer(_texCoordSlot, 2, GL_FLOAT, GL_FALSE,stride, textureOffset);    

        objectToDraw.vertexBufferObject = [objectToDraw createAndBindVBO];
        objectToDraw.vertexArrayObject = _vao;
        glBindBuffer(GL_ARRAY_BUFFER, 0);
        glBindVertexArrayOES(0);

        #else

        objectToDraw.vertexBufferObject = [objectToDraw createAndBindVBO];

        #endif
    }

   // Texture binding removed for clarity     

    #ifdef USE_VAO

    // This code crashes with EXC_BAD_ACCESS on the glDrawElements  

    glBindVertexArrayOES(objectToDraw.vertexArrayObject);
    glDrawElements(GL_TRIANGLES, sizeof(Indices) / sizeof(Indices[0]), GL_UNSIGNED_SHORT,0);
    glBindVertexArrayOES(0);                

    #else        

    // This path works fine. So turning VAO off works :(

    glBindBuffer(GL_ARRAY_BUFFER, storyTile.vertexBufferObject);
    glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, stride, 0);
    glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, stride, colourOffset);
    glVertexAttribPointer(_texCoordSlot, 2, GL_FLOAT, GL_FALSE, stride, textureOffset);

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

    #endif

} // End for each object

[_context presentRenderbuffer:GL_RENDERBUFFER];

}

最后，我的创建和绑定(bind) VBO 方法如下所示；

-(GLuint) createAndBindVBO {

const float* rgba = CGColorGetComponents([self.colour CGColor]);

Vertex Vertices[] = {
    {{0, 1, 0}, {1, 0, 1, 1}, {0,1}},
    {{0, 0, 0}, {1, 0, 1, 1}, {0,0}},
    {{1, 1, 0}, {1, 0, 1, 1}, {1,1}},
    {{1, 0, 0}, {1, 0, 1, 1}, {1,0}}

};

// Code removed for clarity - sets up geometry and colours    

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

return vertexBuffer;
}

我尝试了各种排列组合，并在代码中加入了 glGetError() 以查看这是否有助于指出问题所在。唉，除了调用 drawElements 时出现 BAD_ACCESS 崩溃外，我没有收到任何错误。

编辑:正如所建议的，不幸的是这也不起作用

objectToDraw.vertexBufferObject = [objectToDraw createVBO];

glGenVertexArraysOES(1,&_vao);
glBindVertexArrayOES(_vao);
glBindBuffer(GL_ARRAY_BUFFER, objectToDraw.vertexBufferObject);

glVertexAttribPointer(_positionSlot, 3, GL_FLOAT, GL_FALSE, stride, 0);
glVertexAttribPointer(_colorSlot, 4, GL_FLOAT, GL_FALSE, stride, colourOffset);
glVertexAttribPointer(_texCoordSlot, 2, GL_FLOAT, GL_FALSE,stride, textureOffset);    

objectToDraw.vertexArrayObject = _vao;
glBindVertexArrayOES(0);

我一定是在用顶点数组对象做一些愚蠢的事情......但是有人能找出问题所在吗？

Answer 1

顶点数组启用标志是 VAO 状态的一部分，因此您需要在绑定(bind) VAO 时使用 glEnableVertexAttribArray 启用顶点属性数组。

发件人:http://www.khronos.org/registry/gles/extensions/OES/OES_vertex_array_object.txt

The resulting vertex array object is a new state vector, comprising all the state values (listed in Table 6.2, except ARRAY_BUFFER_BINDING):

• VERTEX_ATTRIB_ARRAY_ENABLED
• VERTEX_ATTRIB_ARRAY_SIZE,
• VERTEX_ATTRIB_ARRAY_STRIDE,
• VERTEX_ATTRIB_ARRAY_TYPE,
• VERTEX_ATTRIB_ARRAY_NORMALIZED,
• VERTEX_ATTRIB_ARRAY_POINTER,
• ELEMENT_ARRAY_BUFFER_BINDING,
• VERTEX_ATTRIB_ARRAY_BUFFER_BINDING.