DDA绘制算法

Question

我正在使用WinBGIm。

#include <iostream>
#include <cmath>
#include "graphics.h"

void Swap(double &a, double &b)
{
    double x = a;
    a = b;
    b = x;
}

double Round(double number)
{
     return (number >= 0) ? (int)(number + 0.5) : (int)(number - 0.5);
}

void PlotPixel(int x, int y, int color)
{
    const int radius = 1;
    setcolor(color);
    circle(400+x,300-y,radius);
}

void DDALine(double x1, double y1, double x2, double y2, int color)
{
    //Is it really required?
    if(x1>x2 || y1>y2)
    {
        Swap(x1, x2);
        Swap(y1, y2);
    }
    //////////////////////???

    double xi = x1;
    double yi = y1;
    double deltaY = y2 - y1;
    double deltaX = x2 - x1;
    double m  = deltaY / deltaX;

    //Is it really required?
    /*if(x1 == x2)
    {
        m = 2;
    }*/

    if(abs(m)<=1)
    {
        while (xi<=x2)
        {
            yi = yi + m;
            yi = Round(yi);
            PlotPixel(xi, yi, color);
            xi = xi + 1;
        }       
    }
    if(abs(m)>1)
    {
        while (yi<=y2)
        {
            xi = xi + 1/m;
            xi = Round(xi);
            PlotPixel(xi, yi, color);
            yi = yi + 1;
        }   
    }   
}

int main()
{
    int gm=DETECT, gd=DETECT;
    initwindow(1024, 800,"Er");

    DDALine(-200, 0, 200, 0, BLUE);
    DDALine(0, 200, 0, -200, BLUE);
    ///////////////////////////////
    DDALine(-100, -100, -100, -100, WHITE);
    DDALine(-100, -100, -100, 100, WHITE);
    DDALine(-100, -100, 100, -100, WHITE);
    DDALine(-100, -100, 100, 100, WHITE);
    DDALine(-100, 100, -100, -100, WHITE);
    DDALine(-100, 100, -100, 100, WHITE);
    DDALine(-100, 100, 100, -100, WHITE);
    DDALine(-100, 100, 100, 100, WHITE);
    /////////////////////////////
    DDALine(100, -100, -100, -100, WHITE);
    DDALine(100, -100, -100, 100, WHITE);
    DDALine(100, -100, 100, -100, WHITE);
    DDALine(100, -100, 100, 100, WHITE);
    DDALine(100, 100, -100, -100, WHITE);
    DDALine(100, 100, -100, 100, WHITE);
    DDALine(100, 100, 100, -100, WHITE);
    DDALine(100, 100, 100, 100, WHITE);



    getch();
    closegraph();
}

输出：

Answer 1

只画直线或45度线

这里的代码似乎是错误的：

while (xi<=x2) { yi = yi + m; yi = Round(yi); PlotPixel(xi, yi, color); xi = xi + 1; }

您在每一步都舍入yi，这意味着在每一步中，您都要向yi添加0或1。这意味着你只能画直线或45度的线。相反，您应该做的是保持yi不四舍五入，但在圆角位置绘制像素，如下所示：

    while (xi<=x2)
    {
        yi = yi + m;
        PlotPixel(xi, Round(yi), color);
        xi = xi + 1;
    }

当然，另一个循环需要以同样的方式修复。我还建议将m反转一次，而不是每次循环一次。另外，您不需要其他的if语句，它可能只是一个else。全面变动：

if(abs(m)<=1)
{
    while (xi<=x2)
    {
        yi = yi + m;
        PlotPixel(xi, Round(yi), color);
        xi = xi + 1;
    }       
}
else
{
    m = 1/m;
    while (yi<=y2)
    {
        xi = xi + m;
        PlotPixel(Round(xi), yi, color);
        yi = yi + 1;
    }   
}