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Can't render quads

Started by lildragon555 May 20, 2011 at 9:26 PM 3 replies 1.4k views

Original Post

May 20, 2011 at 9:26 PM

I attempted to create a simple box just placing points...but for some reason they come out as triangles instead of quads...
Any idea?

//Top
 glBegin(GL_QUADS);
 glVertex3f(0.0f, -4.0f, 0.0f);
 glVertex3f(5.0f, -4.0f, 0.0f);
 glVertex3f(0.0f, -4.0f, -5.0f);
 glVertex3f(5.0f, -4.0f, -5.0f);
 
 //Bottom
 glVertex3f(0.0f, -2.0f, 0.0f);
 glVertex3f(5.0f, -2.0f, 0.0f);
 glVertex3f(0.0f, -2.0f, -5.0f);
 glVertex3f(5.0f, -2.0f, -5.0f);
 
 //Left Side
 glVertex3f(0.0f, -4.0f, 0.0f);
 glVertex3f(0.0f, -4.0f, -5.0f);
 glVertex3f(0.0f, -2.0f, 0.0f);
 glVertex3f(0.0f, -2.0f, -5.0f);
 
 //Right Side
 glVertex3f(5.0f, -4.0f, 0.0f);
 glVertex3f(5.0f, -4.0f, -5.0f);
 glVertex3f(5.0f, -2.0f, 0.0f);
 glVertex3f(5.0f, -2.0f, -5.0f);
 
 //Front Side
 glVertex3f(0.0f, -4.0f, -5.0f);
 glVertex3f(5.0f, -4.0f, -5.0f);
 glVertex3f(0.0f, -2.0f, -5.0f);
 glVertex3f(5.0f, -2.0f, -5.0f);
 
 //Back Side
 glVertex3f(0.0f, -4.0f, 0.0f);
 glVertex3f(5.0f, -4.0f, 0.0f);
 glVertex3f(0.0f, -2.0f, 0.0f);
 glVertex3f(5.0f, -2.0f, 0.0f);
 glEnd();

bluntman

May 20, 2011 at 9:40 PM

All polygons are broken down into triangles before rasterization on the graphics card. So when you switch to wireframe rendering (which I am guessing is how you saw the triangles) you will see the edges of the finally rendered triangles. I believe there is a method to stop these from being rendered by flagging edges on your model for display.

lildragon555

May 20, 2011 at 9:59 PM

All polygons are broken down into triangles before rasterization on the graphics card. So when you switch to wireframe rendering (which I am guessing is how you saw the triangles) you will see the edges of the finally rendered triangles. I believe there is a method to stop these from being rendered by flagging edges on your model for display.

No it isn't in wireframe mode...it's in fill mode...

Brother Bob

May 20, 2011 at 11:14 PM

The vertices of your all your quads are defined in a zig-zag order, like a Z, and not clockwise or counter-clockwise around the quad. The order of your vertices are very important. It should be enough to swap the order of the last two vertices of all quads to at least have the vertices define a proper quad. There may be other problems, such as inconsistent winding order and backface culling, that will break your cube.

lildragon555

May 20, 2011 at 11:49 PM

The vertices of your all your quads are defined in a zig-zag order, like a Z, and not clockwise or counter-clockwise around the quad. The order of your vertices are very important. It should be enough to swap the order of the last two vertices of all quads to at least have the vertices define a proper quad. There may be other problems, such as inconsistent winding order and backface culling, that will break your cube.

Thanks man...didn't know the vertices had to be in order...

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