中点法画圆_2021秋季《计算机图形学》_基于《计算机图形学（第四版）》D.H.&M.P.B...

工具：vscode+glfw

自己写的非常丑陋的代码

// g++ circle.cpp -o test libglfw3dll.a libopengl32.a
// .\test

#include <bits/stdc++.h>
#include <GL/gl.h>
#include "glfw3.h"

#define N 1000

using namespace std;

void processInput(GLFWwindow *window)
{
    if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}

void DrawBresenhamCircle(float r)
{
    float x0 = 0, y0 = r;
    float p = (3-2*r)/1000;
    float x = x0, y = y0;
    for(int i = 0; x<=y && i<1000; i++)
    {
        glBegin(GL_POINTS);
        glVertex2f(x, y);
        glVertex2f(y, x);
        glVertex2f(x, -y);
        glVertex2f(-y,x);
        glVertex2f(-x, y);
        glVertex2f(y, -x);
        glVertex2f(-x, -y);
        glVertex2f(-y, -x);
        if(p>=0)
        {
            p += (4000*(x-y) +10)/1000;
            x+=0.001;
            y-=0.001;
        }
        else
        {
            p += (4000*x+6)/1000;
            x += 0.001;
        }
        glEnd();
    }
}

int main()
{

    if (!glfwInit()) return -1;

    GLFWwindow* window;

    window = glfwCreateWindow(960, 960, "TestOpenGL", NULL ,NULL); //创建窗口对象

    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    while (!glfwWindowShouldClose(window))
    {
        processInput(window);

        //int r; cin>>r;
        DrawBresenhamCircle(1);

        glfwSwapBuffers(window);

        glfwPollEvents();
    }

    glfwTerminate();
    
    return 0;
}

从书上抄的漂亮代码

// g++ Circle_class.cpp -o test libglfw3dll.a libopengl32.a
// .\test

#include <bits/stdc++.h>
#include <GL/gl.h>
#include "glfw3.h"

using namespace std;


class screenPt
{
    private:
        GLint x, y;
    public:
        ScreenPt()
        {
            x = y = 0;  // 默认在原点
        }

        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)  // 自定义画点函数
{
    glBegin(GL_POINTS);
        glVertex2f((float)(xCoord)/1000, (float)(yCoord)/1000);
    glEnd;
}

void circleMidpoint(GLint xc, GLint yc, GLint radius)  // 将圆心坐标和半径传入
{
    screenPt circPt;

    GLint p = 1-radius;

    circPt.setCoords(0, radius);  // 起始位置在圆的最上端

    void circlePlotPoints(GLint, GLint, screenPt);  // 在每个八分之一圆弧起点画一个点
    circlePlotPoints(xc, xc, circPt);

    while (circPt.getx()<=circPt.gety())
    {
        circPt.incrementx();
        if(p<0)
            p += 2*circPt.getx()+1;
        else
        {
            p += 2*(circPt.getx()-circPt.gety())+5;
            circPt.decrementy();
        }
        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 processInput(GLFWwindow *window)
{
    if(glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
        glfwSetWindowShouldClose(window, true);
}


int main()
{
    if (!glfwInit()) return -1;

    GLFWwindow* window;

    window = glfwCreateWindow(960, 960, "MidPointCircle", NULL ,NULL); //创建窗口对象

    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    while (!glfwWindowShouldClose(window))
    {
        processInput(window);

        circleMidpoint(0, 0, 500);

        glfwSwapBuffers(window);

        glfwPollEvents();
    }

    glfwTerminate();
    
    return 0;
}

漂亮但是有一些小问题。由于glfw窗口坐标区间为(-1,1)，所以画点时需要对数据进行/N的处理（可理解为归一化）。由于精度问题，连接处容易产生空缺，画出这样的赛博朋克圆

但在助教的电脑上跑出来就是完整的圆，很离谱，实验课解决。