Thread: GL_QUADS Problem

  1. #1

    GL_QUADS Problem

    For some reason, whenever I try to make a quad with OpenGL, it always has a clear triangle in it. I included a picture that show an example of it.

  2. #2
    C++ Developer XSquared's Avatar
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    Code please.
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  3. #3
    Code:
    void Render(void)
    {
    	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    
    	glPushMatrix();
    	glTranslatef(-1.0f, -1.0f, 0.0f);
    	glRotatef(SpinX, 1.0, 0.0, 0.0);
    	glRotatef(SpinY, 0.0, 1.0, 0.0);
    	glRotatef(SpinZ, 0.0, 0.0, 1.0);
    	glBegin(GL_TRIANGLES);
    		glColor3f(1.0f, 1.0f, 1.0f);
    		glVertex3f(0.0f, 0.0f, 0.0f);
    		glVertex3f(0.0f, 2.0f, 0.0f);
    		glVertex3f(2.0f, 0.0f, 0.0f);
    		glColor3f(1.0f, 0.0f, 0.0f);
    		glVertex3f(0.0f, 0.0f, 3.0f);
    		glVertex3f(0.0f, 2.0f, 3.0f);
    		glVertex3f(2.0f, 0.0f, 3.0f);
    	glEnd();
    	glBegin(GL_QUADS);
    		glColor3f(0.0f, 1.0f, 0.0f);
    		glVertex3f(0.0f, 0.0f, 0.0f);
    		glVertex3f(0.0f, 0.0f, 3.0f);
    		glVertex3f(2.0f, 0.0f, 0.0f);
    		glVertex3f(2.0f, 0.0f, 3.0f);
    	glEnd();
    	glPopMatrix();
    
    	glutSwapBuffers();
    }

  4. #4
    Pursuing knowledge confuted's Avatar
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    Just looking at that picture... it looks like a shadow.
    Away.

  5. #5
    it's not, because if you rotate the image you can see right through it

  6. #6
    Crazy Fool Perspective's Avatar
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    you are drawing the vertices in the wrong order...

    Code:
    you are doing this...
    
    1----2
        /
       /
      /
    3----4
    
    you need to do this
    
    4--3
       |
       |
    1--2
    edit: ascii art
    Last edited by Perspective; 07-04-2003 at 11:53 PM.

  7. #7
    I guess I should look up the order of vertices again

    thx

  8. #8
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    or turn off culling

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