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Cohen-Sutherland 編碼裁剪演算法 C 語言完整實作

編輯：關於C

演算法原理

將平面分為 9 區域，以 4-bit 編碼表示端點位置（左/右/下/上）。依據編碼快速判斷線段完全內部/外部/需裁剪，再透過參數方程求交點迭代裁剪。

完整程式碼（Turbo C 圖形庫）

#include <stdio.h>
#include <graphics.h>

#define LEFT   1
#define RIGHT  2
#define BOTTOM 4
#define TOP    8
#define FALSE  0
#define TRUE   1

int get_code(float x, float y,
             float xmin, float ymin, float xmax, float ymax) {
    int code = 0;
    if (y > ymax) code |= TOP;
    else if (y < ymin) code |= BOTTOM;
    if (x > xmax) code |= RIGHT;
    else if (x < xmin) code |= LEFT;
    return code;
}

void Line_Clipping(float x1, float y1, float x2, float y2,
                   float xmin, float ymin, float xmax, float ymax) {
    int draw = FALSE, done = FALSE;
    int code1 = get_code(x1, y1, xmin, ymin, xmax, ymax);
    int code2 = get_code(x2, y2, xmin, ymin, xmax, ymax);
    float x, y;
    int code;

    while (!done) {
        if ((code1 | code2) == 0) { draw = TRUE; done = TRUE; }
        else if (code1 & code2) { done = TRUE; }
        else {
            code = code1 ? code1 : code2;
            if (code & TOP) {
                y = ymax;
                x = x1 + (y - y1) * (x2 - x1) / (y2 - y1);
            } else if (code & BOTTOM) {
                y = ymin;
                x = x1 + (y - y1) * (x2 - x1) / (y2 - y1);
            } else if (code & RIGHT) {
                x = xmax;
                y = y1 + (x - x1) * (y2 - y1) / (x2 - x1);
            } else if (code & LEFT) {
                x = xmin;
                y = y1 + (x - x1) * (y2 - y1) / (x2 - x1);
            }

            if (code == code1) {
                x1 = x; y1 = y;
                code1 = get_code(x1, y1, xmin, ymin, xmax, ymax);
            } else {
                x2 = x; y2 = y;
                code2 = get_code(x2, y2, xmin, ymin, xmax, ymax);
            }
        }
    }
    if (draw) { setcolor(8); line((int)x1, (int)y1, (int)x2, (int)y2); }
}

int main(void) {
    float x1=76, y1=40, x2=60, y2=80;
    float xmin=50, xmax=80, ymin=50, ymax=70;
    int gdriver = DETECT, gmode;
    initgraph(&gdriver, &gmode, "C:\\TURBOC2");
    setcolor(5);
    line((int)x1, (int)y1, (int)x2, (int)y2);
    rectangle((int)xmin, (int)ymin, (int)xmax, (int)ymax);
    getch();
    cleardevice();
    setcolor(8);
    rectangle((int)xmin, (int)ymin, (int)xmax, (int)ymax);
    Line_Clipping(x1, y1, x2, y2, xmin, ymin, xmax, ymax);
    getch();
    closegraph();
    return 0;
}