c语言实现扫描线填充算法并给出代码

扫描线填充算法是一种用于计算机图形学中的多边形填充方法。它的基本思路是将多边形沿着 y 轴方向分成若干条线段，然后对每条线段进行处理。具体实现过程如下：

1. 扫描线初始化：找出多边形的最高点和最低点，然后依次扫描每一行，从上往下扫描。

2. 建立边表：扫描多边形的每条边，建立边表，包括边的起点、终点、斜率等信息。

3. 建立活性边表：对于每一个扫描线，建立一个活性边表，表示当前扫描线与多边形相交的边。

4. 填充像素：对于每一个扫描线，从左到右扫描活性边表，确定相邻两条边的交点，将这些点之间的像素填充。

下面是 C 语言实现扫描线填充算法的代码：

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

struct Edge {
    int y_upper;  // 边的上端点
    float x_inter;  // 边与扫描线的交点
    float slope_inverse;  // 边的斜率的倒数
};

void add_edge(struct Edge *edges, int *num_edges, int y_upper, float x_inter, float slope_inverse) {
    int i = *num_edges;
    while (i > 0 && y_upper < edges[i - 1].y_upper) {
        edges[i] = edges[i - 1];
        i--;
    }
    edges[i].y_upper = y_upper;
    edges[i].x_inter = x_inter;
    edges[i].slope_inverse = slope_inverse;
    (*num_edges)++;
}

void fill_polygon(int *poly_points, int num_points, int color) {
    struct Edge edges[num_points], edge;
    int num_edges = 0;
    int y, i, j, x1, y1, x2, y2;
    for (i = 0; i < num_points; i++) {
        x1 = poly_points[2 * i];
        y1 = poly_points[2 * i + 1];
        x2 = poly_points[(2 * i + 2) % (2 * num_points)];
        y2 = poly_points[(2 * i + 3) % (2 * num_points)];
        if (y1 == y2) continue;
        if (y1 > y2) {
            int temp = y1;
            y1 = y2;
            y2 = temp;
            temp = x1;
            x1 = x2;
            x2 = temp;
        }
        edge.y_upper = y2 - 1;
        edge.x_inter = x1 + (float)(y_upper - y1) / (y2 - y1) * (x2 - x1);
        edge.slope_inverse = (float)(x2 - x1) / (y2 - y1);
        add_edge(edges, &num_edges, edge.y_upper, edge.x_inter, edge.slope_inverse);
    }
    int scan_line_y = edges[0].y_upper;
    while (scan_line_y >= edges[num_edges - 1].y_upper) {
        int num_intersections = 0;
        float intersections[num_points];
        for (i = 0; i < num_edges; i++) {
            if (scan_line_y < edges[i].y_upper) continue;
            if (edges[i].slope_inverse == 0) continue;
            intersections[num_intersections++] = edges[i].x_inter;
        }
        sort(intersections, intersections + num_intersections);
        for (i = 0; i < num_intersections; i += 2) {
            int x_start = intersections[i];
            int x_end = intersections[i + 1];
            for (j = x_start; j < x_end; j++) {
                putpixel(j, scan_line_y, color);
            }
        }
        scan_line_y--;
        for (i = 0; i < num_edges; i++) {
            if (scan_line_y < edges[i].y_upper) {
                edges[i].x_inter += edges[i].slope_inverse;
            }
        }
    }
}

int main() {
    int poly_points[] = {100, 100, 200, 50, 300, 100, 250, 200, 150, 200};
    int num_points = sizeof(poly_points) / sizeof(int) / 2;
    int color = YELLOW;
    initwindow(640, 480);
    fill_polygon(poly_points, num_points, color);
    getch();
    closegraph();
    return 0;
}

注意：该代码仅供参考，实际应用中仍需根据具体情况进行调整和优化。