opengl vbo, ibo 등을 위한 함수 설명 및 ibo 그려보기

index buffer object를 그리기 위해 glDrawElements를 찾다가 stackoverflow에 좋은 글이 있었다.

stackoverflow.com/a/2949191 (Creative Commons BY-SA, Jonathan Hartley)

 

glDrawElements를 사용해보기 위해 아래 코드로 ㄷ자 모양을 그려보았다.(빈 공간이 -z 방향을 향하도록)

 

 

#include  

GLfloat vertex[] = { 
    0.0, 0.0, 0.0, 
    1.0, 0.0, 0.0, 
    1.0, 1.0, 0.0, 
    0.0, 1.0, 0.0, 
    0.0, 0.0, 1.0, 
    1.0, 0.0, 1.0, 
    1.0, 1.0, 1.0, 
    0.0, 1.0, 1.0 
}; 

GLfloat color[] = { 
    0.3f, 0.4f, 0.2f, 
    0.3f, 0.4f, 0.2f, 
    0.3f, 0.4f, 0.2f, 
    0.3f, 0.4f, 0.2f, 
    0.3f, 0.4f, 0.2f, 
    0.3f, 0.4f, 0.2f, 
    0.3f, 0.4f, 0.2f, 
    0.3f, 0.4f, 0.2f 
}; 

GLfloat normal[] = { 
    -1, 0, 0, 
    1, 0, 0, 
    0, 0, -1 
}; 

GLubyte index[] = { 
    0, 4, 7, 3, 
    1, 2, 6, 5, 
    4, 5, 6, 7 
}; 

void displayAxis(float t) { 
    glBegin(GL_LINE_LOOP); 
    glColor3f(t, 0.0, 0.0); 
    glVertex3f(0.0, 0.0, 0.0); 
    glVertex3f(t, 0.0, 0.0); 
    glEnd(); 
    glBegin(GL_LINE_LOOP); 
    glColor3f(0.0, t, 0.0); 
    glVertex3f(0.0, 0.0, 0.0); 
    glVertex3f(0.0, t, 0.0); 
    glEnd(); 
    glBegin(GL_LINE_LOOP); 
    glColor3f(0.0, 0.0, t); 
    glVertex3f(0.0, 0.0, 0.0); 
    glVertex3f(0.0, 0.0, t); 
    glEnd(); 
} 
void displayFaces() { 
    glEnableClientState(GL_VERTEX_ARRAY); 
    glEnableClientState(GL_COLOR_ARRAY); 
    glVertexPointer(3, GL_FLOAT, 0, vertex); 
    glColorPointer(3, GL_FLOAT, 0, color); 
    glNormalPointer(3, 0, normal); 
    glDrawElements(GL_POLYGON, 4, GL_UNSIGNED_BYTE, index); 
    glDrawElements(GL_POLYGON, 4, GL_UNSIGNED_BYTE, &index[4]); 
    glDrawElements(GL_POLYGON, 4, GL_UNSIGNED_BYTE, &index[8]); 
    glDrawElements(GL_POLYGON, 4, GL_UNSIGNED_BYTE, &index[12]); 
} 
void display(void) 
{ 
    glMatrixMode(GL_MODELVIEW); 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    glLineWidth(2.0); 

    glPushMatrix(); 

    gluLookAt(5.0, 5.0, 5.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0); 

    displayAxis(5.0); 
    displayFaces(); 

    glPopMatrix(); 
    glFlush(); 
} 

void reshape(int x, int y) 
{ 
    glViewport(0, 0, x, y); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    gluPerspective(100.0, (GLdouble)x / (GLdouble)y, 5.0, 30.0); 
} 

void idle(void) 
{ 
    display(); 
} 

int main(int argc, char** argv) 
{ 
    glutInit(&argc, argv); 
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); 
    glutInitWindowSize(800, 600); 
    glutCreateWindow("opengl"); 

    glutDisplayFunc(display); 
    glutReshapeFunc(reshape); 
    glutIdleFunc(idle); 
    glutMainLoop(); 
    return 0; 
}