Boundary and nonboundary edge flags 다각형의 경계선 설정하기

Each vertex of a polygon, separate triangle, or separate quadrilateral specified between a glBegin/glEnd pair is marked as the start of either a boundary or nonboundary edge. If the current edge flag is TRUE when the vertex is specified, the vertex is marked as the start of a boundary edge. If the current edge flag is FALSE, the vertex is marked as the start of a nonboundary edge.

OpenGL에서 선을 그릴때 다각형의 경계선인지 숨겨야할 내부선인지 결정 할 수 있다.

#include <gl/glut.h>
 
void DoDisplay();
 
int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutCreateWindow("OpenGL");
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    glutDisplayFunc(DoDisplay);
    glutMainLoop();
 
    return 0;
}
 
void DoDisplay()
 
{
    glClear(GL_COLOR_BUFFER_BIT);
 
    glPushMatrix();
 
    glTranslatef(-0.5f, 0.0f, 0.0f);
 
    // 첫 번째 선 Nonboundary 지정
    glBegin(GL_TRIANGLES);
    glEdgeFlag(GL_FALSE);   // 경계선 적용 여부를 선택할 선의 시작점 선언 전에 glEdgeFlag()를 호출.
    // Flags edges as either boundary or nonboundary.
    glVertex2f(0.0f, 0.2f);
    glEdgeFlag(GL_TRUE);
    glVertex2f(-0.2f, -0.2f);
    glVertex2f(0.2f, -0.2f);
    glEnd();
 
    glTranslatef(0.5f, 0.0f, 0.0f);
 
    // 두 번째 선 Nonboundary 지정
    glBegin(GL_TRIANGLES);
    glVertex2f(0.0f, 0.2f);
    glEdgeFlag(GL_FALSE);
    glVertex2f(-0.2f, -0.2f);
    glEdgeFlag(GL_TRUE);
    glVertex2f(0.2f, -0.2f);
    glEnd();
 
    glTranslatef(0.5f, 0.0f, 0.0f);
 
    // 세 번째 선 Nonboundary 지정
    glBegin(GL_TRIANGLES);
    glVertex2f(0.0f, 0.2f);
    glVertex2f(-0.2f, -0.2f);
    glEdgeFlag(GL_FALSE);
    glVertex2f(0.2f, -0.2f);
    glEdgeFlag(GL_TRUE);    
    glEnd();
 
    glPopMatrix();
 
    glFlush();
}

Run the program.