c&OpenGL实现计算机图形学：双步绘制直线法绘制菱形
#include <windows.h>
#include <math.h>
#include "glut.h"
int x,y;//用这两个全局变量传递当前窗口的大小。
void init(void)
{
glClearColor(1.0,1.0,1.0,0.0);
glMatrixMode(GL_PROJECTION);
gluOrtho2D(-150.0,150.0,-150.0,150.0);
}
int sign(int x)
{
if(x == 0)
{
return 0;
}
else
{
if(x>0)
return 1;
else
return -1;
}
}
void Doublestep(GLint x0,GLint y0,GLint x1,GLint y1)
{
x0*=y/300;y0*=y/300;x1*=y/300;y1*=y/300;//此行代码用于保持坐标与窗口相对位置不变
GLint d,dx,dy,current_x = x0,current_y = y0,cond;//声明有用的临时变量
dx = abs(x1-x0); dy = abs(y1-y0);
int s_x = sign(x1-x0); int s_y = sign(y1-y0);
cond = 2*dx;
d = 4*dy-dx;
bool is_changed;//标明，象限改变了，dx和dy互相颠倒过了。是改变了的。
if(dy>dx)
{//此时与标准情况正好相反，如果本来x坐标增加，现在变为y坐标增加
int temp = dx;
dx = dy;
dy = temp;
is_changed = true;
}
else
is_changed = false;
for(int i = 1;i<=dx;i+=2)
{
if(d<0)
{ //绘制水平两点，即第一种情况,k<1/4。
glVertex2i(current_x,current_y);//1
if(is_changed)current_y+=s_y;//2
else
current_x+=s_x;
glVertex2i(current_x,current_y);
if(is_changed)current_y+=s_y;//3
else
current_x+=s_x;
}
else
{
if(d<cond)
{ //绘制第二种情况，k=>1/4 && k<2/4
glVertex2i(current_x,current_y);//1
if(is_changed)current_y+=s_y;//2
else
current_x+=s_x;
glVertex2i(current_x,current_y);
current_x+=s_x;current_y+=s_y;//3
}
else if(d<2*cond)
{ //绘制三种情况，k<=2/4 && k<3/4
glVertex2i(current_x,current_y);//1
current_x+=s_x;current_y+=s_y;//2
glVertex2i(current_x,current_y);
if(is_changed)current_y+=s_y;//3
else
current_x+=s_x;
}
else
{ //绘制第四种情况，k>=3/4
glVertex2i(current_x,current_y);//1
current_x+=s_x;current_y+=s_y;//2
glVertex2i(current_x,current_y);
current_x+=s_x;current_y+=s_y;//3
d-=2*dx;//情况4单独减2dx
}
d-=2*dx;//2,3,4情况统一减2dx
}
d+=4*dy;//所有情况统一加4dy;
}
}
void displayfunc(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0,1.0,0.0);
//坐标轴。
glBegin(GL_LINES);
glVertex2i(-x/2,0);
glVertex2i(x/2-1,0);
glEnd();
glBegin(GL_LINES);
glVertex2i(0,-y/2);
glVertex2i(0,y/2);
glEnd();
glColor3f(1.0,0.0,0.0);
glBegin(GL_POINTS);
//菱形的4条边************//*
Doublestep(-100,0,0,-150);//*
Doublestep(100,0,0,-150);//*
Doublestep(100,0,0,150);//*
Doublestep(-100,0,0,150);//*
//***********************//*
glEnd();
glFlush();
}
void myReshapeFunc(GLsizei w,GLsizei h)
{
x = w;y = h;
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
//令坐标系统和窗口大小变化对应，即坐标始终和窗口大小保持1：1，
//否则窗口放大后所画直线将变成虚线，即画点的坐标偏离预期坐标。
gluOrtho2D(-w/2.0+0.5,w/2.0+0.5,-h/2.0+0.5,h/2.0+0.5);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity ();
glClear(GL_COLOR_BUFFER_BIT);
}
int main(int argc, char** argv)
{
glutInit(&argc,argv);
glutInitDisplayMode(GLUT_SINGLE|GLUT_RGB);
glutInitWindowPosition(300,300);
glutInitWindowSize(301,301);
glutCreateWindow("My DrawRhombus Program");
init();
glutReshapeFunc (myReshapeFunc);
glutDisplayFunc(displayfunc);
glutMainLoop();
return 0;
}