Rotations- help?

Hi All-
I am new to OpenGL and was wondering if anyone could offer some suggestions. I coded up a pyramid (rectangular base, triangular sides) by plotting all the vertices and currently each side is a different color. Hypothetically, we start with a red side and as it rotates it should go away in the back and then come back up as it makes the full 360. However, when I used glRotate it looks fine at first, but before the pyramid does a full rotation the front side somehow becomes transparent and I can see that red face in the back before it comes around. To avoid this problem, I thought I might be able to move the “camera” around, to view different parts of the pyramid to simulate a rotation instead of using glRotate. Any help is greatly appreciated! Thanks :slight_smile:

  • check you request a depth buffer (aka. zbuffer).
  • check all triangles are CCW (counterclockwise) from the visible side.

Hey, thanks! For your second tip, do you mean check that the order I coded the triangles are CCW? / What’s the reasoning behind that?

Another problem that arose was that the faces were rotating individually and not as a single pyramidal object, so is that another pro for just moving the “camera” around instead of directly calling glRotate?

ZbuffeR said that vertices in your triangles must be specified in CCW order, reason behind that is backface culling. Quick reference: http://en.wikipedia.org/wiki/Back-face_culling ,
You can change this setting by calling glFrontFace ( http://www.opengl.org/documentation/specs/man_pages/hardcopy/GL/html/gl/frontface.html )

To rotate whole object, call glRotatef before drawing that object.

ps. Sorry about my poor English.

Alternatively, you can disable backface culling(glDisable(GL_CULL_FACE)), but for larger scenes you should have it on as it improves performance.