//生成一个纹理，将纹理 id 赋值给 m_TextureId
glGenTextures(1, &m_TextureId); 

//将纹理 m_TextureId 绑定到类型 GL_TEXTURE_2D 纹理
glBindTexture(GL_TEXTURE_2D, m_TextureId);

//设置纹理 S 轴（横轴）的拉伸方式为截取
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); 
//设置纹理 T 轴（纵轴）的拉伸方式为截取
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

//设置纹理采样方式
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

//加载 RGBA 格式的图像数据
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_RenderImage.width, m_RenderImage.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[0]);

#version 300 es                                     
precision mediump float;                            
in vec2 v_texCoord;                                 
layout(location = 0) out vec4 outColor;             
uniform sampler2D s_TextureMap; //声明采用器                     
void main()                                         
{
  // texture() 为内置的采样函数，v_texCoord 为顶点着色器传进来的纹理坐标
  // 根据纹理坐标对纹理进行采样，输出采样的 rgba 值（4维向量）                                                  
  outColor = texture(s_TextureMap, v_texCoord);      
}                                                   

// 生成纹理，编译链接着色器程序
void TextureMapSample::Init()
{
    //create RGBA texture
    glGenTextures(1, &m_TextureId);
    glBindTexture(GL_TEXTURE_2D, m_TextureId);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glBindTexture(GL_TEXTURE_2D, GL_NONE);

    char vShaderStr[] =
            "#version 300 es                            \n"
            "layout(location = 0) in vec4 a_position;   \n"
            "layout(location = 1) in vec2 a_texCoord;   \n"
            "out vec2 v_texCoord;                       \n"
            "void main()                                \n"
            "{                                          \n"
            "   gl_Position = a_position;               \n"
            "   v_texCoord = a_texCoord;                \n"
            "}                                          \n";

    char fShaderStr[] =
            "#version 300 es                                     \n"
            "precision mediump float;                            \n"
            "in vec2 v_texCoord;                                 \n"
            "layout(location = 0) out vec4 outColor;             \n"
            "uniform sampler2D s_TextureMap;                     \n"
            "void main()                                         \n"
            "{                                                   \n"
            "  outColor = texture(s_TextureMap, v_texCoord);     \n"
            "}                                                   \n";

    m_ProgramObj = GLUtils::CreateProgram(vShaderStr, fShaderStr, m_VertexShader, m_FragmentShader);
    if (m_ProgramObj)
    {
        m_SamplerLoc = glGetUniformLocation(m_ProgramObj, "s_TextureMap");
    }
    else
    {
        LOGCATE("TextureMapSample::Init create program fail");
    }

}

// 加载图像数据、纹理坐标和顶点坐标数据，绘制实现纹理映射
void TextureMapSample::Draw(int screenW, int screenH)
{
    LOGCATE("TextureMapSample::Draw()");

    if(m_ProgramObj == GL_NONE || m_TextureId == GL_NONE) return;
    GLfloat verticesCoords[] = {
            -1.0f,  0.5f, 0.0f,  // Position 0
            -1.0f, -0.5f, 0.0f,  // Position 1
            1.0f, -0.5f, 0.0f,  // Position 2
            1.0f,  0.5f, 0.0f,  // Position 3
    };

    GLfloat textureCoords[] = {
            0.0f,  0.0f,        // TexCoord 0
            0.0f,  1.0f,        // TexCoord 1
            1.0f,  1.0f,        // TexCoord 2
            1.0f,  0.0f         // TexCoord 3
    };

    GLushort indices[] = { 0, 1, 2, 0, 2, 3 };

    //upload RGBA image data
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, m_TextureId);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, m_RenderImage.width, m_RenderImage.height, 0, GL_RGBA, GL_UNSIGNED_BYTE, m_RenderImage.ppPlane[0]);
    glBindTexture(GL_TEXTURE_2D, GL_NONE);

    // Use the program object
    glUseProgram (m_ProgramObj);

    // Load the vertex position
    glVertexAttribPointer (0, 3, GL_FLOAT,
                            GL_FALSE, 3 * sizeof (GLfloat), verticesCoords);
    // Load the texture coordinate
    glVertexAttribPointer (1, 2, GL_FLOAT,
                            GL_FALSE, 2 * sizeof (GLfloat), textureCoords);

    glEnableVertexAttribArray (0);
    glEnableVertexAttribArray (1);

    // Bind the RGBA map
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, m_TextureId);

    // Set the RGBA map sampler to texture unit to 0
    glUniform1i(m_SamplerLoc, 0);

    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, indices);

}