无法绘制Bresenham，OpenGL

#include <GL/glut.h>

void drawLine(int x0, int y0, int x1, int y1) {
    int dx = abs(x1 - x0);
    int dy = abs(y1 - y0);
    int sx = (x0 < x1) ? 1 : -1;
    int sy = (y0 < y1) ? 1 : -1;
    int err = dx - dy;

    while (true) {
        glBegin(GL_POINTS);
        glVertex2i(x0, y0);
        glEnd();

        if (x0 == x1 && y0 == y1) break;

        int e2 = 2 * err;
        if (e2 > -dy) {
            err -= dy;
            x0 += sx;
        }
        if (e2 < dx) {
            err += dx;
            y0 += sy;
        }
    }
}

void display() {
    glClear(GL_COLOR_BUFFER_BIT);

    glColor3f(1.0, 1.0, 1.0);
    drawLine(100, 100, 400, 300);

    glFlush();
}

int main(int argc, char** argv) {
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("Bresenham Line");
    glClearColor(0.0, 0.0, 0.0, 0.0);
    gluOrtho2D(0, 500, 0, 500);
    glutDisplayFunc(display);
    glutMainLoop();

    return 0;
}