画线算法 [DDA] [中点画线] [Bresenham]

[DDA] [中点画线] [Bresenham]

画线要用到的坐标系区域表示：

逐点比较算法流程：

Bresenham的算法流程图：

Code：

#include<GL/glut.h>#include<math.h>#pragma comment(linker,"/subsystem:\&;windows\&; /entry:\&;mainCRTStartup\&;")//DDA画法（依据斜率）void DDA(int x1,int y1,int x2,int y2){int k,i;float x,y,dx,dy;if(abs(x2-x1) < abs(y2-y1)) //斜率的绝对值大于1，每次沿y方向加减一个单位//以大的为准，应该是精度高呗k = abs(y2-y1);else k = abs(x2-x1);dx = float(x2-x1)/k;dy = float(y2-y1)/k;//〒_〒，这点写错了，float是必须的，要不整除会变成0，纠结我好长时间x = float(x1);y = float(y1);glColor3f(1.0f,1.0f,0.0f);glPointSize(5);for(i=0;i<k;i++){glBegin(GL_POINTS);glVertex2i((int)(x+0.5),(int)(y+0.5));glEnd();x += dx;y += dy;}}//中点画线算法（模拟/逐点比较）void MidPointLine(int x1,int y1,int x2,int y2){int a,b,dt1,dt2,d,x,y;a = y1 – y2;b = x2 – x1;d = a + a + b;//为了避免小数，这里取2倍dt1 = a + b + a +b;dt2 = a + a;x = x1;y = y1;glColor3f(1.0f,0.0f,0.0f);glBegin(GL_POINTS);glVertex2i(x,y);glEnd();while(x < x2){if(d < 0){x++;y++;d += dt1;}else{x++;d += dt2;}glBegin(GL_POINTS);glVertex2i(x,y);glEnd();}}//Bresenham画线算法（插值法）void Bresenham(int x1,int y1,int x2,int y2){int x,y,dx,dy,d,d1,d2,inc,temp;dx = x2 – x1;dy = y2 – y1;if(dx*dy >= 0)inc = 1;elseinc = -1;glColor3f(0.0f,1.0f,0.0f);if(abs(dx) > abs(dy)){if(dx < 0)//将2a,3a区域的直线变换到1a,4a区域{temp = x1;x1 = x2;x2 = temp;temp = y1;y1 = y2;y2 = temp;dx = -dx;dy = -dy;}d = 2 * dy – dx;d1 = 2 * dy;d2 = 2 * (dy – dx);x = x1;y = y1;glBegin(GL_POINTS);glVertex2i(x,y);glEnd();while(x < x2){x++;if(d < 0)d += d1;else{y += inc;d += d2;}glBegin(GL_POINTS);glVertex2i(x,y);glEnd();}}else{if(dy < 0)//将3b,4b区域的直线变换到1b,2b区域{temp = x1;x1 = x2;x2 = temp;temp = y1;y1 = y2;y2 = temp;dx = -dx;dy = -dy;}d = 2 * dx -dy;d1 = 2 * dx;d2 = 2 * (dx-dy);x = x1;y = y1;glBegin(GL_POINTS);glVertex2i(x,y);glEnd();while(y < y2){y++;if(d < 0)d += d1;else{x += inc;d += d2;}glBegin(GL_POINTS);glVertex2i(x,y);glEnd();}}}void myDisplay(void){glShadeModel(GL_FLAT);//GL_FLAT为默认mode，可省略/*void glShadeModel(GLenum mode)mode取值为GL_FLAT,则多边形的颜色取决于最后一个点。mode取值为GL_SMOOTH，则多边形被分割为多个三角形，然后进行平滑着色。glShadeModel(GL_FLAT):用指定多边形最后一个顶点时的当前颜色作为填充多边形的纯色，唯一例外是GL_POLYGON图元，它采用的是第一个顶点的颜色。glShadeModel(GL_SMOOTH):从各个顶点给三角形投上光滑的阴影，为各个顶点指定的颜色之间进行插值*/glClearColor(0.0f,1.0f,1.0f,0.0f);glClear(GL_COLOR_BUFFER_BIT);DDA(300,100,0,0);//调用DDA函数画线，黄色的~MidPointLine(0,0,400,200); //红色的Bresenham(0,0,100,300);//绿色的glFlush();}void Reshape(int w,int h){glViewport(0,0,(GLsizei)w,(GLsizei)h);//调整像素矩形，用于绘制整个窗口glMatrixMode(GL_PROJECTION); //这三个函数调整绘图坐标，使左下角位置为(0,0),右上角位置为(w,h)glLoadIdentity(); gluOrtho2D(0.0,(GLdouble)w,0.0,(GLdouble)h); }/*Reshape函数：在GLUT内部，，将给该函数传递两个参数：窗口被移动或修改后的宽度和高度，单位为像素*/int main(int argc,char * argv[]){glutInit(&argc,argv);glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);glutInitWindowPosition(300,100);glutInitWindowSize(450,450);glutCreateWindow("DRAWLINE in different ways");glutDisplayFunc(myDisplay);glutReshapeFunc(Reshape);//该函数用于重新建立用作新渲染画布的矩形区域，定义绘制物体时使用的坐标系glutMainLoop();return 0;}

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