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Correcting Flipped Surface Normals1:48 with Jason Baskin
We have seen how surface normals can influence the appearance of a model to make edges appear smooth or faceted, but when working with game assets it is also important that we make sure our normals have not been flipped or inverted.
Important Commands and Hotkeys:
- Shading>Backface Culling from the camera view activates single-sided display.
- Mesh Display>Reverse from the Main Menu reverses the direction of normals for the selected faces.
We've already seen how surface normals can influence the appearance of a model to
suggest added detail, and make edges appear smooth or faceted.
But when working with game assets,
it's also important that we make sure our normals haven't been flipped or inverted.
Looking at a model in Maya, inverted normals can sometimes be hard to spot.
Because Maya displays all polygon faces as two sided objects.
For example, we can see a basic polygon plane from both the top and bottom view.
But game engines don't typically display both sides of a polygon face.
Because two-sided rendering requires a lot more processing
power from the graphics card.
The back sides of polygons are displayed with solid black shading in Maya.
Which can be a helpful clue that a face is reversed.
But another easy way to confirm that surface normals are oriented correctly
is to activate the single sided display setting by clicking on the check box
next to shading, backface culling in your camera view.
Culling is just a technical term for ignoring or hiding.
And the backface is just the backside of a face, as you might have guessed.
I typically leave backface culling activated as my default setting
whenever I'm creating models that will be used in a game.
Inverted normals are sometimes produced during the extrusion process, and
they can also appear if an object is given a negative scaling value.
Artists often create symmetrical models by building just one side of the model,
then duplicating objects and scaling them to a value of -1 to create a mirror image.
In some cases, this can invert normals.
If you find any inverted normals on a mesh, the fix is very simple.
Just select the problem faces, then go to the main menu and choose mesh display,
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