Planar Quads in Blender – Making Faces Flat

I’ve seen a lovely flat shaded rendering style yesterday and while trying to emulate it, I noticed it’s important to have quads actually being flat for flat shaded rendering. As the rendering system splits everything into triangles, having a non-flat quad results in a edge that is visible as both triangles of the quad will have a slightly different shading. To my surprise, no good information on how to make a polygon flat could be found on the net…

The easiest way that I came up with to make a non-axis aligned polygon flat is this:

  1. Change the Transformation Orientation Mode from Global to Normal(combo box next to the transformation gizmo settings)
  2. Change the vertex snapping mode from Increment to Vertex and deactivate it (the little magnet is grayed out, combo box next to it shows two dots on a cube)
  3. Select three vertices that form the final plane you want the quad to lie in.
  4. Press Ctrl+Alt+Space to create a new custom orientation (transformation coordinate system), give it some name and make sure the Overwrite Previous is turned on. The coordinate system’s z-axis will be orthogonal to our defined plane (left part of the screenshot).
  5. Now select the off-plane vertex, press g to translate, and twice z to limit the transformation to the newly created coordinate system’s z axis (notice the blue line in the right part of the screenshot).
  6. Press and hold ctrl and move the mouse cursor over one of the three reference vertices so that the transformation snaps its z-value to that vertex (notice the orange snap circle in the right part of the screenshot).
  7. Release the mouse button and voila, the quad is now perfectly flat.

Since we enabled “Overwrite Previous”, for the next quad one just has to select three vertices, press ctrl+alt+space (overwriting the previously generated coordinate system), g, z, z, hold ctrl and move over a reference vertex (to snap), release, done. Sounds complicated at first but it’s actually very fast to do. Hope that helps


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