1. 实验目的
练习直线和圆的光栅扫描线算法。
2. 实验内容和要求
按要求完成以下两个作业。提交纸质实验报告，同时提交实验报告和源代码的电子版。
(I). 利用Bresenham直线扫描算法绘制任意直线段。输入为起点坐标(x0,y0)和终点坐标(x1,y1)以及线宽w,利用Bresenham算法计算离散的近似像素点，并在OpenGL窗口中绘制该线段。要求绘制至少五条线段，具有不同的斜率，不同的起点和终点，不同的线宽。
不允许直接调用GL_LINES来实现。
(II). 利用中点画圆算法绘制圆。输入为圆心(xc,yc)和圆的的半径r，利用中点画圆算法计算离散的近似像素点，并在OpenGL窗口中绘制。要求绘制至少四个圆，构成一个图案，比如奥迪车标或五环。
建议：为了实现坐标点和像素的一一对应，建议坐标轴的范围和窗口像素宽高一致，比如：glutInitWindowSize(800, 600);//像素宽800，高600
坐标系设定为：gluOrtho2D(-400, 400, -300, 300);//坐标轴x方向宽为800，y方向高为600
3.实验结果
（1）划线：程序源代码

#include "pch.h"
#include<stdlib.h>
#include<GL/glut.h>
#include<math.h>

void init(void) {
    
	glClearColor(1.0, 1.0, 1.0, 1.0);

	glMatrixMode(GL_PROJECTION);
	gluOrtho2D(-400.0, 400.0, -300.0, 300.0);
}

//通过描点来划线。
void setPixel(int x, int y, int w) {
    
	int m = w / 2, n = w - m;
	glColor3f(1, 0, 0);
	for (int i = -m; i < n; i++) {
    
		glBegin(GL_POINTS);
		glVertex2i(x + i, y);
		glEnd();
	}

}
void lineBres(int x0, int y0, int xEnd, int yEnd, int w) {
    
	int dx = fabs(xEnd - x0), dy = fabs(yEnd - y0);
	int x, y, p, twoDy, twoDyMinudDx, m, f;
	m = dy / dx;
	//斜率小于一
	if (m == 0) {
    
		p = 2 * dy - dx;     //p0
		twoDy = 2 * dy;
		twoDyMinudDx = 2 * (dy - dx);    //当pk<0时，调用twoDy；当pk>0时，调用twoDyMinudDx
		if (x0 > xEnd) {
    
			x = xEnd;
			y = yEnd;
			xEnd = x0;
			f = 0;
		}
		else {
    
			x = x0;
			y = y0;
			f = 1;
		}
		setPixel(x, y, w);
		while (x < xEnd) {
    
			x++;
			if (p < 0)
				p += twoDy;
			else {
    
				if (yEnd > y0&&f == 0 || yEnd < y0&&f == 1)      //多次试验，总结出来，说不出来
					y--;
				else
					y++;
				p += twoDyMinudDx;
			}
			setPixel(x, y, w);
		}
	}
	else {
    
		p = 2 * dx - dy;     //p0
		twoDy = 2 * dx;
		twoDyMinudDx = 2 * (dx - dy);    //当pk<0时，调用twoDy；当pk>0时，调用twoDyMinudDx
		//斜率绝对值大于一
		if (y0 > yEnd) {
    
			x = xEnd;
			y = yEnd;
			yEnd = y0;
			f = 0;
		}
		else {
    
			x = x0;
			y = y0;
			f = 1;
		}
		setPixel(x, y, w);
		while (y < yEnd) {
    
			y++;
			if (p < 0)
				p += twoDy;
			else {
    
				if (xEnd > x0&&f == 0 || xEnd < x0&&f == 1)      //多次试验，总结出来，说不出来
					x--;
				else
					x++;
				p += twoDyMinudDx;
			}
			setPixel(x, y, w);
		}
	}
}

void lineSegment(void) {
    
	glClear(GL_COLOR_BUFFER_BIT);
	glColor3f(0, 0, 0);
	//坐标轴
	glBegin(GL_LINES);
	glVertex2i(0, -250);
	glVertex2i(0, 250);
	glVertex2i(-300, 0);
	glVertex2i(300, 0);
	glEnd();
	glBegin(GL_TRIANGLES);        //三个点一组
	glVertex2i(-10, 250);             //坐标
	glVertex2i(0, 260);             //坐标
	glVertex2i(10, 250);             //坐标
	glVertex2i(300, 10);             //坐标
	glVertex2i(310, 0);             //坐标
	glVertex2i(300, -10);             //坐标
	glEnd();
	lineBres(10, 10, 100, 200, 3);
	lineBres(10, 10, 200, 100, 4);
	lineBres(-10, 10, -100, 200, 5);
	lineBres(-10, 10, -200, 100, 6);
	lineBres(-10, -10, -200, -100, 6);
	lineBres(-10, -10, -100, -200, 5);
	//lineBres(-50, 0, 200, -300 ,3);   //通过这个慢慢总结出来 xEnd>x0&&f==0
	//lineBres(0, 0, -100, 100 ,3);    //通过这个慢慢总结出来 xEnd<x0&&f==1
	lineBres(10, -10, 200, -100, 4);
	lineBres(10, -10, 100, -200, 3);
	glFlush();
}

void main(int argc, char** argv) {
    
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
	glutInitWindowPosition(100, 100);
	glutInitWindowSize(800, 600);
	glutCreateWindow("Bresenham算法划线");
	init();
	glutDisplayFunc(lineSegment);
	glutMainLoop();
}

运行结果：

（2）画圆程序源代码

**#include"pch.h"
#include<GL/glut.h>
#include<stdio.h>
#include"iostream"

void init(void) {
    
	glClearColor(1.0, 1.0, 1.0, 1.0);

	glMatrixMode(GL_PROJECTION);
	gluOrtho2D(-400.0, 400.0, -300.0, 300.0);
}

class screenPt {
    
private:
	GLint x, y;
public:
	sreenPt() {
    
		x = y = 0;
	}
	void setCoords(GLint xCoordValue, GLint yCoordValue) {
    
		x = xCoordValue;
		y = yCoordValue;
	}
	GLint getx()const {
    
		return x;
	}
	GLint gety()const {
    
		return y;
	}
	void incrementx() {
    
		x++;
	}
	void decrementy() {
    
		y--;
	}
};

void setPixel(GLint xCoord, GLint yCoord) {
    
	glColor3f(0, 0, 0);
	glBegin(GL_POINTS);
	glVertex2i(xCoord, yCoord);
	glEnd();
}

void circleMidpoint(GLint xc, GLint yc, GLint radius) {
    
	screenPt circPt;

	GLint p = 1 - radius;
	circPt.setCoords(0, radius);
	void circlePlotPoints(GLint, GLint, screenPt);
	circlePlotPoints(xc, yc, circPt);
	while (circPt.getx() < circPt.gety()) {
    
		circPt.incrementx();
		if (p < 0)
			p += 2 * circPt.getx() + 1;
		else {
    
			circPt.decrementy();
			p += 2 * (circPt.getx() - circPt.gety()) + 1;
		}
		circlePlotPoints(xc, yc, circPt);
	}
}

void circlePlotPoints(GLint xc, GLint yc, screenPt circPt) {
    
	setPixel(xc + circPt.getx(), yc + circPt.gety());
	setPixel(xc - circPt.getx(), yc + circPt.gety());
	setPixel(xc + circPt.getx(), yc - circPt.gety());
	setPixel(xc - circPt.getx(), yc - circPt.gety());
	setPixel(xc + circPt.gety(), yc + circPt.getx());
	setPixel(xc - circPt.gety(), yc + circPt.getx());
	setPixel(xc + circPt.gety(), yc - circPt.getx());
	setPixel(xc - circPt.gety(), yc - circPt.getx());
}

void lineSegment(void) {
    
	glClear(GL_COLOR_BUFFER_BIT);
	circleMidpoint(0, 100, 100);
	circleMidpoint(-80, 190, 20);
	circleMidpoint(80, 190, 20);
	circleMidpoint(0, 50, 50);
	circleMidpoint(-40, 99, 10);
	circleMidpoint(40, 99, 10);
	circleMidpoint(0, 90, 8);
	glFlush();
}

void main(int argc, char** argv) {
    
	glutInit(&argc, argv);
	glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
	glutInitWindowPosition(100, 100);
	glutInitWindowSize(800, 600);
	glutCreateWindow("Bresenham算法画圆");

	init();
	glutDisplayFunc(lineSegment);

	glutMainLoop();
}
**

运行结果