OpenGL中Bresenham画线算法，就是画不出东西。麻烦大神帮忙看看

[57_Viking]

//------------Bresenham画线算法---------------------
//--------------by D_Viking-------------------------
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<GL/glut.h>



/*Bresenham line-drawing procedure for |m|<1.0 */
void init(void){
	glClearColor(1.0, 1.0, 1.0, 0.0);//Set display-window color to white.
	glMatrixMode(GL_PROJECTION);//Set projection parameters.
	gluOrtho2D(0.0, 550.0, 0.0, 550.0);	
}

void setPixel(GLint x, GLint y){
	glClear(GL_COLOR_BUFFER_BIT | GL_COLOR_BUFFER_BIT);
	
	
	glBegin(GL_POINTS);
	    glColor3f(1, 0, 0);//Set line segment color to green.
	    glVertex2i(x, y);
		glPointSize(9);//绘制前设置点的大小和颜色
	glEnd();
	glFlush();
}

void lineBres(){
	int x0, y0, xEnd, yEnd;
	//scanf_s("%d", &x0); scanf_s("%d", &xEnd); scanf_s("%d", &y0); scanf_s("%d", ¥d);
	x0 = 60; y0 = 300; xEnd = 100; yEnd = 400;
	glClear(GL_COLOR_BUFFER_BIT);//Clear display window.
	
	glColor3f(1, 0, 0);//Set line segment color to green.
	int dx = (int)fabs((float)xEnd - x0), dy = (int)fabs((float)yEnd - y0);
	int p = 2 * dy - dx;
	int twoDy = 2 * dy, twoDyMinusDx = 2 * (dy - dx);
	int x, y;
	/*Determine which endpoint to use as start position.*/

	if (x0 > xEnd){
		x = xEnd;
		y = yEnd;
		xEnd = x0;
	}
	else
	{
		x = x0;
		y = y0;
	}
	setPixel(x, y);
	while (x < xEnd){
		x++;
		if (p < 0)
			p += twoDy;
		else
		{
			y++;
			p += twoDyMinusDx;
		}
		setPixel(x, y);
	}
}

void main(int argc, char** argv){
	glutInit(&argc, argv);//Initialize GLUT.
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);//Set display mode.
	glutInitWindowPosition(50, 100);//Set top-left display-window position.
	glutInitWindowSize(400, 300);//Set display-window width and height.
	glutCreateWindow("Bresenham画线算法");//Create display window.

	init();//Execute initialization procedure.
	glutDisplayFunc(lineBres);//Send graphics to display window.
	
	glutMainLoop();//Display everything and wait.
}

[fly_dragon_fly]

没有设置modelview矩阵, 稍微向z-偏一点