Question

OpenGL初学者，下面这段代码运行结果为什么不是一个系列点，而只有一个点？请高手指点。多谢。

#include<gl/glaux.h>
#include<GL/glut.h>
#include<gl/GL.h>
void myDisplay(void)
{
float dx,dy,y,k;
int x,x0=0,y0=0;
float x1=200,y1=300;
dx=x1-x0,dy=y1-y0;
k=dy/dx,y=y0;
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0f,0.0f,1.0f);
glPointSize(5.0f);
for(x=x0;x<x1;x++)
{
glBegin(GL_POINTS);
glVertex2d(x,(y+0.5));
glEnd();
y=y+k;
}
glFlush();
}
int main(int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
glutInitWindowPosition(0, 0);
glutInitWindowSize(400, 400);
glutCreateWindow("第一个OpenGL程序");
glutDisplayFunc(&myDisplay);
glutMainLoop();
return 0;
}

Answer 1

窗口的默认大小范围是从-1到1，当然显示不了别的点了。1.需要添加一个控制窗口大小范围的函数，void ChangeSize()。2.在主函数main（）中添加一句glutReshapeFunc(ChangeSize);

显示结果，点比较密集，显示如下

#include<gl/glaux.h>
#include<GL/glut.h>
#include<gl/GL.h>
void myDisplay(void)
{
    float dx,dy,y,k;
    int x,x0=0,y0=0;
    float x1=200,y1=300;
    dx=x1-x0,dy=y1-y0;
    k=dy/dx,y=y0;
    glClearColor(1,1,1,1);//设置背景颜色为白色
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0f,0.0f,1.0f);
    glPointSize(2.0f);
    for(x=x0;x<x1;x++)
    {
        glBegin(GL_POINTS);
        glVertex2d(x,(y+0.5));    
        glEnd();
        y=y+k;
    }
    glFlush();
}

//添加的函数
void ChangeSize(GLsizei w,GLsizei h)
{
	GLfloat aspectRatio;
	GLfloat nRange=400.0f;
	if(h==0)
		h=1;
	glViewport(0,0,w,h);
	aspectRatio=(GLfloat)w/(GLfloat)h;
	
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
 
	 if (w <= h)    
	   glOrtho (-nRange, nRange, -nRange*h/w, nRange*h/w, -nRange*5.0f, nRange*5.0f);
   else 
        glOrtho (-nRange*w/h, nRange*w/h, -nRange, nRange, -nRange*5.0f, nRange*5.0f);
	
	glMatrixMode(GL_MODELVIEW);
	glLoadIdentity();
}


int main(int argc, char *argv[])
{    
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutInitWindowPosition(0, 0);
    glutInitWindowSize(400, 400);
    glutCreateWindow("第一个OpenGL程序");
    glutReshapeFunc(ChangeSize);//添加的语句
    glutDisplayFunc(&myDisplay);
    glutMainLoop();
    return 0;
}