problem in drawing cricle by GL_POINT in opengl

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

C++

#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();
}

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

Posted 13-Oct-13 7:22am

Mohammad Sharify

Updated 13-Oct-13 10:23am

Nelek

v2

Add a Solution

4 solutions

Solution 2

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

C++

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

EDIT: Oh, and also add

C++

glLoadIdentity();

under your glClear(...) call

Posted 12-Nov-13 23:10pm

Singender Holzkuebel

Updated 12-Nov-13 23:13pm

v2

Comments

adiqais 12-Dec-13 0:55am

I did everything at the end it didn't work white screen

Singender Holzkuebel 12-Dec-13 2:53am

Ok, I think i found the bug now.
Replace "glBegin(GL_POINT);" with "glBegin(GL_POINTS);". You are parsing the wrong "GL_POINT" argument, which should be "GL_POINTS".

See my new post for the working code.

adiqais 12-Dec-13 3:10am

where in my code I have glBegin(GL_POINT);
check the below code ...

Singender Holzkuebel 12-Dec-13 3:13am

I used the code from your original post.

Solution 3

C#

#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

Posted 11-Dec-13 18:54pm

adiqais

Solution 4

Working code!

C++

#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 );

  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  //glOrtho(0.0, 500.0, 500.0, 0.0, 1.0, -1.0); //As an example
  glOrtho(-1.0, 1.0, 1.0, -1.0, 1.0, -1.0); //Look up glOrtho to know what this does ;)
  glMatrixMode(GL_MODELVIEW);
}
void display(void)
{
  glClear(GL_COLOR_BUFFER_BIT);
  glLoadIdentity();
  // drawing

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

  glBegin(GL_POINTS);

  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();
}

Your mistakes were:

C++

glBegin(GL_POINT);

"GL_POINT" is used for other OpenGL functions. Valid arguments for glBegin are:
GL_POINTS
GL_LINES
GL_LINE_STRIP
GL_LINE_LOOP
GL_TRIANGLES
GL_TRIANGLE_STRIP
GL_TRIANGLE_FAN
GL_QUADS
GL_QUAD_STRIP
GL_POLYGON

Mistake #2

C++

void init()
{
  ...
}

In your init function you forgot to initialize the projection matrix.
This matrix does all the magic behind converting OpenGL unit coordinates to screen coordinates.

That's it. If you have any question feel free to ask.

Posted 11-Dec-13 21:10pm

Singender Holzkuebel

Updated 11-Dec-13 21:48pm

v2

Comments

adiqais 12-Dec-13 3:50am

I did exactly what you pointed above nothing change, also #include "stdafx.h" error shown

Singender Holzkuebel 12-Dec-13 4:04am

What operating system are you working on?

adiqais 12-Dec-13 4:12am

windows 8

Singender Holzkuebel 12-Dec-13 4:17am

Then you probably have to change your includes to something like:
#include <gl gl.h="">
#include <gl glut.h=""> //Or maybe just glut.h, depends on where your compiler searches for glut.

If stdafx.h can't be found, remove the include.
You should know how to manage your own includes...

adiqais 12-Dec-13 4:22am

I ve tried it all with without include thanks a lot, I ll keep trying

Mohammad Sharify 16-Dec-13 13:57pm

tnx alot,it solved!

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Arashdn · Accepted Answer · 2013-10-13T08:46:00

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

C++

#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();
}

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

C++

#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();
}