OpenGL中GL_POINT绘制冰柱的问题 [英] problem in drawing cricle by GL_POINT in opengl

问题描述

我想用GL_POINT在opengl中绘制一个小钉，这里有我的代码:

I want draw a cricle in opengl by GL_POINT and there is my code:

#include "stdafx.h"
#include <glut.h>
#include <math.h>

const float PI =3.141592653;
void init()
{
	glClearColor(1,1,1,0);
	glShadeModel(GLU_FLAT);
	glPointSize( 6.0 );
}
void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT);
	// drawing

	float x,y;
	glColor3f(0,0,1);
	
		glBegin(GL_POINT);
	
		for ( float angle = 0; angle <= 2*PI; angle+=0.1)
	{
		x =( .3) * cos (angle);
		y =( .3) * sin (angle);

		glVertex2f(x,y);
		
	}
	
	
	glEnd();

	glutSwapBuffers();
}
void main(int argc , char * argv[])
{
	glutInit(& argc , argv);
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);

	// Window of drawing
	glutInitWindowSize(500,500);
	glutInitWindowPosition(100 , 100);
	glutCreateWindow("my first program");
	init();
	glutDisplayFunc(display);
	glutMainLoop();
}

但是当我运行程序时，我只会看到一个白色的窗口！，如果您有解决此问题的想法，请帮助我.
tnx:)

but when I run program I just see a white window!,if you have idea to solve it pliz help me.
tnx :)

推荐答案

您必须将glBegin和glEnd块放入循环中:

Hi ,
You must put glBegin and glEnd blocks inside the loop:

#include <glut.h>
#include <math.h>

const float PI =3.141592653;
void init()
{
    glClearColor(1,1,1,0);
    glShadeModel(GLU_FLAT);
    glPointSize( 6.0 );
}
void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    // drawing

    float x,y;
    glColor3f(0,0,1);



    for ( float angle = 0; angle <= 2*PI; angle+=0.1)
    {
        x =( 0.3) * cos (angle);
        y =( 0.3) * sin (angle);
        glBegin(GL_POINTS);
        glVertex2f(x,y);
        glEnd();

    }




    glutSwapBuffers();
}
void main(int argc , char * argv[])
{
    glutInit(& argc , argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);

    // Window of drawing
    glutInitWindowSize(500,500);
    glutInitWindowPosition(100 , 100);
    glutCreateWindow("my first program");
    init();
    glutDisplayFunc(display);
    glutMainLoop();
}

如果将点大小更改为default，并在循环中使用更多步骤，则圆圈会更好:

The circle will be nicer , if you change point size to default , and use more steps in loop:

#include <glut.h>
#include <math.h>

const float PI =3.141592653;
void init()
{
    glClearColor(1,1,1,0);
    glShadeModel(GLU_FLAT);
    //glPointSize( 6.0 );
}
void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    // drawing

    float x,y;
    glColor3f(0,0,1);



    for ( float angle = 0; angle <= 2*PI; angle+=0.01)
    {
        x =( 0.3) * cos (angle);
        y =( 0.3) * sin (angle);
        glBegin(GL_POINTS);
        glVertex2f(x,y);
        glEnd();

    }




    glutSwapBuffers();
}
void main(int argc , char * argv[])
{
    glutInit(& argc , argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);

    // Window of drawing
    glutInitWindowSize(500,500);
    glutInitWindowPosition(100 , 100);
    glutCreateWindow("my first program");
    init();
    glutDisplayFunc(display);
    glutMainLoop();
}

我很确定它没有用，因为您没有设置投影矩阵.
将此代码放入您的init函数中:

I''m pretty sure it doesn''t work because you didn''t set up your projection matrix.
Put this code inside your init function:

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 500.0, 500.0, 0.0, 1.0, -1.0); //As an example
glMatrixMode(GL_MODELVIEW);

哦，还要在您的glClear(...)调用下添加

Oh, and also add

glLoadIdentity();

#include <glut.h>
//#include <glu.h>
#include <math.h>

const float PI = 3.141592653;

void init(void)
{
    glClearColor(1,1,1,0);
    glShadeModel(GLU_FLAT);
    glPointSize(6.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0, 500.0, 500.0, 0.0, 1.0, -1.0);
    glMatrixMode(GL_MODELVIEW);
    /**glBegin(GL_POINTS);
    //drawing circle with points
    glClearColor(1,1,1,0);
    glShadeModel(GLU_FLAT);
    glPointSize(6.0);
    //glVertex2f(1.0f,0.2f);
    //glVertex2f(0.5f,-0.5f);
    glEnd;*/
}


void display(void)
{

    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    //drawing
    float x,y;
    glColor3f(0,0,1);

    for(float angle = 0; angle<=2*PI; angle+=0.1)
    {
    x =(0.3)*cos (angle);
    y=(0.)*sin (angle);
    glBegin(GL_POINTS);
    glVertex2f(x,y);
    glEnd;
    }//endFor

    glutSwapBuffers();
    /**glColor3f(1.0,0.0,0.0);
    glVertex3f(1.0f,1.0f,1.0f);
    glColor3f(1.0,0.0,0.0);
    glVertex3f(-1.0f,-1.0f,0.0f);*/

}
void main(int argc, char** argv)
{
    int mode = GLUT_RGB | GLUT_DOUBLE;
        //int mode = GLUT_SINGLE depend of parity of your card
    glutInit(& argc, argv);
    glutInitDisplayMode(mode);//function initializing display mode

    glutInitWindowSize(500,500);// size of window width & height pixel

    glutInitWindowPosition(100,100);//(0,0) left bottom corner position

    glutCreateWindow ("First Project");

    init();

    glutDisplayFunc(display);//name of the Object/Function
    //gluSphere x = new gluSphere();
    glutMainLoop();
    //return 0;
}//endmain

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