#include #include "stdlib.h" void init (void) { glClearColor (1.0, 1.0, 1.0, 0.0); // 指定清空颜色（背景色）为白色 glMatrixMode (GL_PROJECTION); //指定投影矩阵 gluOrtho2D (0.0, 400.0, 0.0, 400.0); //指定二维坐标系中被显示的区域 } typedef struct tEdge { int yUpper; float xIntersect, dxPerScan; struct tEdge * next; } Edge; struct dcPt { //dcPt 实际上是一个点的结构体 int x; int y; }; void setPixel(GLint x, GLint y){ glBegin(GL_POINTS); glVertex2i(x, y); glEnd(); } /* Inserts edge into list in order of increasing xIntersect field. */ void insertEdge (Edge * list, Edge * edge) { Edge * p, * q = list; p = q->next; while (p != NULL) { if (edge->xIntersect < p->xIntersect) p = NULL; else { q = p; p = p->next; } } edge->next = q->next; q->next = edge; } /* For an index, return y-coordinate of next nonhorizontal line */ int yNext (int k, int cnt, dcPt * pts) { int j; if ((k+1) > (cnt-1)) j = 0; else j = k + 1; while (pts[k].y == pts[j].y) if ((j+1) > (cnt-1)) j = 0; else j++; return (pts[j].y); } /* Store lower-y coordinate and inverse slope for each edge. Adjust and store upper-y coordinate for edges that are the lower member of a monotically increasing or decreasing pair of edges */ void makeEdgeRec (dcPt lower, dcPt upper, int yComp, Edge * edge, Edge * edges[]) { edge->dxPerScan = (float) (upper.x - lower.x) / (upper.y - lower.y); edge->xIntersect = lower.x; if (upper.y < yComp) edge->yUpper = upper.y - 1; else edge->yUpper = upper.y; insertEdge (edges[lower.y], edge); } void buildEdgeList (int cnt, dcPt * pts, Edge * edges[]) { Edge *edge; dcPt v1, v2; int i, yPrev = pts[cnt - 2].y; v1.x = pts[cnt-1].x; v1.y = pts[cnt-1].y; for (i=0; i if (v1.y != v2.y) { /* nonhorizontal line */ edge=(Edge *) malloc (sizeof (Edge)); if (v1.y < v2.y) /* up-going edge */ makeEdgeRec (v1, v2, yNext (i, cnt, pts), edge, edges); else /* down-going edge */ makeEdgeRec (v2, v1, yPrev, edge, edges); } yPrev = v1.y; v1 = v2; } } void buildActiveList (int scan, Edge * active, Edge * edges[]) { Edge * p, * q; p = edges[scan]->next; while (p) { q = p->next; insertEdge (active, p); p = q; } } void fillScan (int scan, Edge * active) { Edge * p1, * p2; int i; p1 = active->next; while (p1) { p2 = p1->next; for (i=p1->xIntersect; i setPixel ((int) i, scan); p1 = p2->next; } } void deleteAfter (Edge * q) { Edge * p = q->next; q->next = p->next; free (p); } /* Delete completed edges. Update 'xIntersect' field for others */ void updateActiveList (int scan, Edge * active) { Edge * q = active, * p = active->next; while (p) if (scan >= p->yUpper) { p = p->next; deleteAfter (q); } else { p->xIntersect = p->xIntersect + p->dxPerScan; q = p; p = p->next; } } void resortActiveList (Edge * active) { Edge * q, * p = active->next; active->next = NULL; while (p) { q = p->next; insertEdge (active, p); p = q; } } void scanFill (int cnt, dcPt * pts) { Edge *edges[400], * active; int i, scan; for (i=0; i<400; i++) { edges[i] = (Edge *) malloc (sizeof (Edge)); edges[i]->next = NULL; } buildEdgeList (cnt, pts, edges); active = (Edge *) malloc (sizeof (Edge)); active->next = NULL; for (scan=0; scan<200; scan++) { buildActiveList (scan, active, edges); if (active->next) { fillScan (scan, active); updateActiveList (scan, active); resortActiveList (active); } } /* Free edge records that have been malloc'ed ... */ } void myDisplay (void) { glClear (GL_COLOR_BUFFER_BIT); // 清空显示窗口 glColor3f (1.0, 0.0, 0.0); // 指定前景色（当前绘制颜色）为蓝色 dcPt pts[] = {250,50,550,150,550,400,250,250,100,350,100,100,120,30}; glBegin(GL_LINES); glVertex2i(180,15); //Specify line-segment geometry. glVertex2i(10,145); glEnd(); scanFill (7,pts); glFlush ( ); // 使绘制立即反映到屏幕上 } void main(int argc, char *argv[]) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE); glutInitWindowPosition(100, 100); glutInitWindowSize(400, 400); glutCreateWindow("扫描线算法！"); init(); glutDisplayFunc(&myDisplay); glutMainLoop(); }下载本文
