Remembering coordinates (Push/Pop Matrix ?)

**janemba** · 01-12-2013, 08:07 AM

Hello,
This is my first post so I would like to say Hello for everyone.
In school I'm programming in openlg and I have problem. That's my code:

Code :

int DrawGLScene(GLvoid)									
{	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	
 
 
x=0.0f;
 
for (i = 0; i < 3; i++)
{
 
	if (keys['1'])	a = 1;
 
	if (keys['2'])	a = 2;
 
 		if (a == 1)
		{	
 
		glLoadIdentity();
		glTranslatef(0, 0.0f,-25.0f);
		glRotatef(rtri,0.0f,1.0f,0.0f);
	//	glPushMatrix();
		glTranslatef(x, 0.0f,0.0f);
 
		glBegin(GL_TRIANGLES);								
		glColor3f(1.0f,0.0f,0.0f);						
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);				  
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f,-1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);
		glEnd();
 
		if (x == 0) x = -3;
		else if (x < 0 ) x = 3;
 
 
		rtri+=0.05f;
 
		}
		if (a == 2) 
 	{	
 
		glLoadIdentity();
		glTranslatef(x, 0.0f,-25.0f);
	//	glPopMatrix();
		glRotatef(rtri,0.0f,1.0f,0.0f);
		glBegin(GL_TRIANGLES);								
		glColor3f(1.0f,0.0f,0.0f);						
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);				  
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f,-1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);
 
		glEnd();
 
		if (x == 0) x = -3;
		else if (x < 0 ) x = 3;
 
 
		rtri+=0.05f;
 
		}
}
 
	return TRUE;										
}

Key '1' nad '2' are changing mode and my problem is how to do, to remember coordinates ? When I put key '2' everything is back to position 0, 0, 0 (efects the same like "translatef (0.0f, 0.0f, 0.0f)". I tried to use glPushMatrix and glPopMatrix but it doesn't work (probably I used these functions wrong). Can help me and correct this code ? Is very very importand for me...
Big Thanks.
ps. Sorry for my english... :/

Best Regards

**tonyo_au** · 01-12-2013, 08:38 PM

glPush and glPop save and restore the current select matrix (in you case you want the VIEWMODEL matrix). So you need to select the view model matrix with glMatrixMode(GL_VIEWMODEL) and call glPushMatrix; now do what ever you want to draw your objects; then call glPopMatrix() and you have the original matrix back.

**janemba** · 01-14-2013, 08:55 AM

Thanks for replay.
I understood, but I did something wrong because it isn't working. Can you correct this code, please ?

Code :

int DrawGLScene(GLvoid)									
{	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);	
 
 
x=0.0f;
 
for (i = 0; i < 3; i++)
{
 
	if (keys['1'])	a = 1;
 
	if (keys['2'])	a = 2;
 
 		if (a == 1)
		{	
 
		glLoadIdentity();
		glTranslatef(0, 0.0f,-25.0f);
		glRotatef(rtri,0.0f,1.0f,0.0f);
 
	 	glPushMatrix();
		glTranslatef(x, 0.0f,0.0f);
		glMatrixMode(GL_MODELVIEW);
		glBegin(GL_TRIANGLES);								
		glColor3f(1.0f,0.0f,0.0f);						
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);				  
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f,-1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);
		glEnd();
 
		if (x == 0) x = -3;
		else if (x < 0 ) x = 3;
 
 
		rtri+=0.05f;
 
		}
		if (a == 2) 
 	{	
 
 		glLoadIdentity();
 		glTranslatef(x, 0.0f,-25.0f);
		glPopMatrix();
		glRotatef(rtri,0.0f,1.0f,0.0f);
		glBegin(GL_TRIANGLES);								
		glColor3f(1.0f,0.0f,0.0f);						
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);				 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f( 1.0f,-1.0f, 1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f( 1.0f,-1.0f, -1.0f);				  
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f, -1.0f);					 
		glColor3f(1.0f,0.0f,0.0f);						 
		glVertex3f( 0.0f, 1.0f, 0.0f);					 
		glColor3f(0.0f,0.0f,1.0f);						 
		glVertex3f(-1.0f,-1.0f,-1.0f);					 
		glColor3f(0.0f,1.0f,0.0f);						 
		glVertex3f(-1.0f,-1.0f, 1.0f);
 
		glEnd();
 
		if (x == 0) x = -3;
		else if (x < 0 ) x = 3;
 
 
		rtri+=0.05f;
 
		}
}
 
	return TRUE;										
}

Where I did mistake ?

**tonyo_au** · 01-16-2013, 01:08 AM

Your push and pops are not paired - you push if a == 1 and only pop if it is equal to 2 - this look wrong.

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