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sujandasmahapatra

OpenGL rotating 2 objects 1 remains static problem opengl

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I want to rotate 2 objects out of 3. One object should remain static. But it’s not happening. Please help. I using glPushMatrix() and glPopMatrix() for the objects that I want to rotate.

 

void CopenGLCoordView::DrawScene(CDC *pDC)
{
    wglMakeCurrent(pDC->m_hDC, m_hrc);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
 
    drawLine();
 
    glLoadIdentity();
    glPushMatrix();
    glRotatef(rot[0], 1.0f, 0.0f, 0.0f);
    glRotatef(rot[1], 0.0f, 1.0f, 0.0f);
    glRotatef(rot[2], 0.0f, 0.0f, 1.0f);
    drawAxes();
    glPrintX("X");
    glPrintY("Y");
    glPrintZ("Z");
    glPopMatrix();
 
    
 
    glFlush();
    SwapBuffers(pDC->m_hDC);    
    wglMakeCurrent(NULL, NULL);
}

 

With the above code nothing is rotating. I want the drawLine() line should be static while the axis and x,y,z should rotate. Please help how can I achieve this?..Thanks Sujan

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blueshogun96    2264

My initial guess is that you might want to call glPushMatrix before glLoadIdentity.  Tbh, I don't think you even need that extra call to glLoadIdentity, unless your drawing function is modifying the model view matrix before returning.  I assume you are properly updating your rotation vector per frame?

 

Also, I'm curious as to what your implementation of drawAxes() looks like, that is, if it has a significant amount of code inside of it.

 

Shogun.

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void CopenGLCoordView::drawAxes()
{
 
    CDC* pDC = GetDC();
    wglMakeCurrent(pDC->m_hDC, m_hrc);
    glBegin(GL_LINES);
    glVertex3f(0.0f, 0.0f, 0.0f); // origin of the line
    glVertex3f(5.0f, 0.0f, 0.0f); // ending point of the 
    glEnd();
       glBegin(GL_LINES);
    glVertex3f(0.0f, 0.0f, 0.0f); // origin of the line
    glVertex3f(0.0f, 5.0f, 0.0f); // ending point of the 
    glEnd();
       glBegin(GL_LINES);
    glVertex3f(0.0f, 0.0f, 0.0f); // origin of the line
    glVertex3f(0.0f, 0.0f, 5.0f); // ending point of the 
    glEnd();
    wglMakeCurrent(NULL,NULL); 
    ReleaseDC(pDC);
}
 
void CopenGLCoordView::drawLine()
{
    CDC* pDC = GetDC();
    wglMakeCurrent(pDC->m_hDC, m_hrc);
    glBegin(GL_LINES);
        glVertex3f(10,0,0);
        glVertex3f(20,0,0);
    glEnd();
    wglMakeCurrent(NULL,NULL);
 
}

These are my drawaxes and drawLine code. Now my drawscene looks like this

 
void CopenGLCoordView::DrawScene(CDC *pDC)
{
    wglMakeCurrent(pDC->m_hDC, m_hrc);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
 
    drawLine();
 
    glPushMatrix();
    glLoadIdentity();
    glRotatef(rot[0], 1.0f, 0.0f, 0.0f);
    glRotatef(rot[1], 0.0f, 1.0f, 0.0f);
    glRotatef(rot[2], 0.0f, 0.0f, 1.0f);
    drawAxes();
    glPrintX("X");
    glPrintY("Y");
    glPrintZ("Z");
    glPopMatrix();
 
    
 
    glFlush();
    SwapBuffers(pDC->m_hDC);    
    wglMakeCurrent(NULL, NULL);
}

 

I have made the glPushMatrix() before glLoadIdentity().......Nothing is rotating...I want only the axes should rotate, line remains fixed in space. Pls help.

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If I put drawLine below the transformation the everything is rotating axes and line both, check below the code. How can I make only the axis should rotate and line remains fixed. Please help.

 

void CopenGLCoordView::DrawScene(CDC *pDC)
{
    wglMakeCurrent(pDC->m_hDC, m_hrc);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    
    glEnable(GL_DEPTH_TEST);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
 
    glPushMatrix();
    glLoadIdentity();
    glRotatef(rot[0], 1.0f, 0.0f, 0.0f);
    glRotatef(rot[1], 0.0f, 1.0f, 0.0f);
    glRotatef(rot[2], 0.0f, 0.0f, 1.0f);
    drawAxes();
    glPrintX("X");
    glPrintY("Y");
    glPrintZ("Z");
    glPopMatrix();
 
    drawLine();
 
    glFlush();
    SwapBuffers(pDC->m_hDC);    
    wglMakeCurrent(NULL, NULL);
}

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blueshogun96    2264

Hmm, this is a tough one.  It should be working as far as I can tell, but it's not...

 

May I ask why you set and unset the OpenGL context in every draw call?  It isn't necessary and it's not very efficient.  You should only set it once per thread.  If you are using only one thread, then only set your context after initialization, and unset it during uninitialization.  I don't know if glPush/PopMatrix() functions work if the OpenGL context isn't set, so I'd recommend not doing this in every single one of your draw calls.

 

Shogun.

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__SKYe    1784

First of all, you only create and set the OpenGL context ONCE when you create the window. You don not want to bind and unbind the OpenGL context every frame.

 

Second, you don't use glFlush() and SwapBuffers()in the same application.

If you created your window using double buffering, then you call only SwapBuffers(). If you didn't create it using double buffering, then you use glFlush().

 

Then, do you ever set a projection matrix in your application?

Something like:

//For 2D

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, 0, width, height);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

//For 3D

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glluPerspective(45.0f, (float)width / height, 0.1f, 100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

You have to set a projection matrix before you draw stuff.

 

After this you don't have to use glLoadIdentity() again, you should use glPushMatrix() and glPopMatrix() to apply transformations to the objects drawn within those calls.

 

Here's some things:

 

//You should call this every frame. Everything that is drawn MUST be called every frame

void CopenGLCoordView::drawAxes()
{
 
    //Do NOT bind the DC every frame, this is only done once when you create the window
    //CDC* pDC = GetDC(); DO NOT
    //wglMakeCurrent(pDC->m_hDC, m_hrc);

    //You don't need to make a glBegin() glEnd() for each line. You can call glBegin(GL_LINES) and glEnd() once
    //and OpenGL knows that every glVertex3f() pairs form a line
    glBegin(GL_LINES);
    glVertex3f(0.0f, 0.0f, 0.0f); // origin of the line
    glVertex3f(5.0f, 0.0f, 0.0f); // ending point of the 

    glVertex3f(0.0f, 0.0f, 0.0f); // origin of the line
    glVertex3f(0.0f, 5.0f, 0.0f); // ending point of the 

    glVertex3f(0.0f, 0.0f, 0.0f); // origin of the line
    glVertex3f(0.0f, 0.0f, 5.0f); // ending point of the 
    glEnd();

    //Again, don't release the context every frame
    //wglMakeCurrent(NULL,NULL); 
    //ReleaseDC(pDC);
}
void CopenGLCoordView::drawLine()
{
    //Again, don't bind the context every frame
    //CDC* pDC = GetDC();
    //wglMakeCurrent(pDC->m_hDC, m_hrc);

    //In a perspective matrix, this line might end up out of the screen
    glBegin(GL_LINES);
        glVertex3f(10,0,0);
        glVertex3f(20,0,0);
    glEnd();

    //No unbinding context here
    //wglMakeCurrent(NULL,NULL);
 
}
void CopenGLCoordView::DrawScene(CDC *pDC)
{
    //Once again, this is a no no
    //wglMakeCurrent(pDC->m_hDC, m_hrc);

    //This correct, as long as you created your window with a depth buffer.
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);    

    //Depth testing is only used for 3D, but if you're drawing 3D, then it is correct
    glEnable(GL_DEPTH_TEST);

    //Here you should set you're projection matrix
    //that could be
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    //Substitute width & height by your window's width & height
    gluPerspective(45.0f, (float)width / height, 0.1f, 100.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    //Also, maybe you'll want to use a gluLookAt() here to set the camera's position
    //If you're not familiar with this function, then you may want to look it up on Google
    gluLookAt(0.0f, 5.0f, 10.0f, 0.0f, 0.0f, 0.0f, 0.0f, 1.0f, 0.0f);
 
    //Every thing drawn within this call and the next glPopMatrix(), will not affect the modelview matrix
    glPushMatrix();

    //This glLoadIdentity is unnecessary
    //glLoadIdentity();

    //This rotations will only affect the drawAxes() call (and the Prints if it matters)
    glRotatef(rot[0], 1.0f, 0.0f, 0.0f);
    glRotatef(rot[1], 0.0f, 1.0f, 0.0f);
    glRotatef(rot[2], 0.0f, 0.0f, 1.0f);
    drawAxes();
    glPrintX("X");
    glPrintY("Y");
    glPrintZ("Z");
    glPopMatrix();
 
    //The rotations above will NOT affect this call
    drawLine();
 
    //Again, use glFlush() if you're window does not support double buffering
    glFlush();

    //Or use SwapBuffers() if it does. Don't use both
    SwapBuffers(pDC->m_hDC);   

    //Once again, do not do this here 
    //wglMakeCurrent(NULL, NULL);
}

 

 

Quite honestly, you don't seem to have an understanding of OpenGL. You might want to perhaps using GLUT to learn, before of jumping to Win32 and OpenGL.

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