전체코드

#include <sb7.h>
#include <math.h>

class singlepoint_app : public sb7::application
{
    void init()
    {
        static const char title[] = "OpenGL SuperBible - Single Point";

        sb7::application::init();

        memcpy(info.title, title, sizeof(title));
    }

    virtual void startup()
    {
        static const char * vs_source[] =
        {
            "#version 410 core                                                 \n"
            "                                                                  \n"
            "layout (location = 0) in vec4 offset;                             \n"
            "                                                                  \n"
            "void main(void)                                                   \n"
            "{                                                                 \n"
            "    const vec4 vertices[] = vec4[](vec4( 0.25, -0.25, 0.5, 1.0),  \n"
            "                                   vec4(-0.25, -0.25, 0.5, 1.0),  \n"
            "                                   vec4( 0.25,  0.25, 0.5, 1.0)); \n"
            "                                                                  \n"
            "    // Add 'offset' to our hard-coded vertex position             \n"
            "    gl_Position = vertices[gl_VertexID] + offset;                 \n"
            "}                                                                 \n"
        };

        static const char * fs_source[] =
        {
            "#version 410 core                                                 \n"
            "                                                                  \n"
            "out vec4 color;                                                   \n"
            "                                                                  \n"
            "void main(void)                                                   \n"
            "{                                                                 \n"
            "    color = vec4(0.0, 0.8, 1.0, 1.0);                             \n"
            "}                                                                 \n"
        };
		
        program = glCreateProgram();
        GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
        glShaderSource(fs, 1, fs_source, NULL);
        glCompileShader(fs);

        GLuint vs = glCreateShader(GL_VERTEX_SHADER);
        glShaderSource(vs, 1, vs_source, NULL);
        glCompileShader(vs);

        glAttachShader(program, vs);
        glAttachShader(program, fs);

        glLinkProgram(program);

        glGenVertexArrays(1, &vao);
        glBindVertexArray(vao);
    }

    virtual void render(double currentTime)
    {
        static const GLfloat green[] = { 0.0f, 0.25f, 0.0f, 1.0f };
        glClearBufferfv(GL_COLOR, 0, green);

        glUseProgram(program);

        GLfloat attrib[] = { (float)sin(currentTime) * 0.5f,
                             (float)cos(currentTime) * 0.6f,
                             0.0f, 0.0f };

        glVertexAttrib4fv(0, attrib); // 1번째 파라미터 쉐이더의 layout (location = 0) 와 대칭

        glDrawArrays(GL_TRIANGLES, 0, 3);
    }

    virtual void shutdown()
    {
        glDeleteVertexArrays(1, &vao);
        glDeleteProgram(program);
    }

private:
    GLuint          program;
    GLuint          vao;
};

DECLARE_MAIN(singlepoint_app)

설명

    virtual void render(double currentTime)
    {
        static const GLfloat green[] = { 0.0f, 0.25f, 0.0f, 1.0f };
        glClearBufferfv(GL_COLOR, 0, green);

        glUseProgram(program);

        GLfloat attrib[] = { (float)sin(currentTime) * 0.5f,
                             (float)cos(currentTime) * 0.6f,
                             0.0f, 0.0f };

        glVertexAttrib4fv(0, attrib); // 1번째 파라미터 쉐이더의 layout (location = 0) 와 대칭

        glDrawArrays(GL_TRIANGLES, 0, 3);
    }

render 함수내

        GLfloat attrib[] = { (float)sin(currentTime) * 0.5f,
                             (float)cos(currentTime) * 0.6f,
                             0.0f, 0.0f };

        glVertexAttrib4fv(0, attrib); // 1번째 파라미터 쉐이더의 layout (location = 0) 와 대칭 

부분을 보면 0값은 

static const char * vs_source[] =
        {
            "#version 410 core                                                 \n"
            "                                                                  \n"
            "layout (location = 0) in vec4 offset;                             \n"
            "                                                                  \n"
            "void main(void)                                                   \n"
            "{                                                                 \n"
            "    const vec4 vertices[] = vec4[](vec4( 0.25, -0.25, 0.5, 1.0),  \n"
            "                                   vec4(-0.25, -0.25, 0.5, 1.0),  \n"
            "                                   vec4( 0.25,  0.25, 0.5, 1.0)); \n"
            "                                                                  \n"
            "    // Add 'offset' to our hard-coded vertex position             \n"
            "    gl_Position = vertices[gl_VertexID] + offset;                 \n"
            "}                                                                 \n"
        };

layout (location = 0) in vec4 offset; 의 offset 변수 인덱스번호를 의미 한다.