#version 100

attribute highp vec2 aPosition;

attribute highp vec2 aTexcoord;

//将顶点数组元素都存入一个缓存对象中

    static const float position[] = {

        -1.0f, -1.0f,0.0f,1.0f,//2 顶点位置 2 纹理坐标

        1.0f, -1.0f,1.0f,0.0f,

        -1.0f, 1.0f,0.0f,1.0f,

        1.0f, 1.0f,1.0f,1.0f

    };

    //-----------基于索引绘制

    static const GLushort plane_indices[] =

    {

        0, 1, 2, 3

    };

    glGenBuffers(1, &_index_buffer);

    glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _index_buffer);

    glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(plane_indices), plane_indices, GL_STATIC_DRAW);

    //--------------

    glGenBuffers(1, &_quad_vbo);

    glBindBuffer(GL_ARRAY_BUFFER, _quad_vbo);

    glBufferData(GL_ARRAY_BUFFER, sizeof(position), NULL, GL_STATIC_DRAW);

    glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(position), position);

    glGenVertexArrays(1, &_vao);

    glBindVertexArray(_vao);

    GLint naPosition = mProgram->getAttribLocation("aPosition");

    glEnableVertexAttribArray(0);

    //注意，这里的offset 是内存中大小的偏移，必须准确计算出内存大小偏移量 sizeof

    glVertexAttribPointer(naPosition, 2, GL_FLOAT, GL_FALSE, 4*sizeof(float), (GLvoid*)0);

    GLint naTexcoord = mProgram->getAttribLocation("aTexcoord");

    glEnableVertexAttribArray(1);

    glVertexAttribPointer(naTexcoord, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(float), (const GLvoid*)(2*sizeof(float)));

    glBindVertexArray(0);

    glDisableVertexAttribArray(0);

    glDisableVertexAttribArray(1);