CPP►algorithm

DDA画线法（考虑所有情况）

使用了第三方图形库EGEv19.01，C++编写。

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#include <cmath>
#include <graphics.h>
#include <iostream>
using namespace std;
void DDA_Line(int x0, int y0, int x1, int y1)
{
    float dx, dy, k, x, y;
    dx = x1 - x0;
    dy = y1 - y0;
    k = dy / dx;
    if (dx == 0) {
        //因为C++除法操作除数为零时候可能会出现undefined的结果
        //简化后续if判断
        k = 1000;
    }
    x = x0;
    y = y0;
    if (k > 0) {
        if (dx > 0) {
            //k>0且dx>0
            if (dy < dx) {
                //0<k<1，步进方向为x，y增量为k
                for (; x <= x1; ++x) {
                    putpixel(x, int(y + 0.5), BLACK);
                    y += k;
                }
            } else {
                //k>=1，步进方向为y，x增量为1/k
                for (; y <= y1; ++y) {
                    putpixel(int(x + 0.5), y, BLACK);
                    x += 1 / k;
                }
            }
        } else {
            //k>0且dx<0，dy<0，此处判断反向画线
            if (abs(dy) < abs(dx)) {
                //0<k<1，步进方向为x，y增量为-k
                for (; x >= x1; --x) {
                    putpixel(x, int(y + 0.5), BLACK);
                    y -= k;
                }
            } else {
                //k>=1，步进方向为y，x增量为-1/k
                for (; y >= y1; --y) {
                    putpixel(int(x + 0.5), y, BLACK);
                    x -= 1 / k;
                }
            }
        }
    } else {
        if (dx > 0) {
            //k<0且dx>0，dy<0
            if (abs(dy) < abs(dx)) {
                //-1<k<0，步进方向为x，y增量为k
                for (; x <= x1; ++x) {
                    putpixel(x, int(y + 0.5), BLACK);
                    y += k;
                }
            } else {
                //k<=-1，步进方向为y，x增量为1/k
                for (; y >= y1; --y) {
                    putpixel(int(x + 0.5), y, BLACK);
                    x -= 1 / k;
                }
            }
        } else {
            //k<0且dx<0，dy>0，此处判断反向画线
            if (abs(dy) < abs(dx)) {
                //-1<k<0，步进方向为x，y增量为-k
                for (; x >= x1; --x) {
                    putpixel(x, int(y + 0.5), BLACK);
                    y -= k;
                }
            } else {
                //k>=-1，步进方向为y，x增量为-1/k
                for (; y <= y1; ++y) {
                    putpixel(int(x + 0.5), y, BLACK);
                    x += 1 / k;
                }
            }
        }
    }
}

int main()
{
    initgraph(640, 480);

    setbkcolor(WHITE);
    DDA_Line(30, 50, 10, 60); //-1<k<0
    DDA_Line(10, 60, 30, 50);

    DDA_Line(30, 50, 10, 90); //k<-1
    DDA_Line(10, 90, 30, 50);

    DDA_Line(30, 50, 10, 40); //0<k<1
    DDA_Line(10, 40, 30, 50);

    DDA_Line(30, 50, 10, 10); //k>1
    DDA_Line(10, 10, 30, 50);

    DDA_Line(10, 90, 10, 10); //k==0,x==10
    DDA_Line(10, 10, 10, 90);

    DDA_Line(30, 50, 10, 50); //k==0,y==50
    DDA_Line(10, 50, 30, 50);

    getch();

    closegraph();
    return 0;
}