BGE missing faces on the mesh

Okay, so it’s all good until I turn on the game engine. Usually, I can flip the normals and it’s all better. But it only makes it worse. Can anyone tell me why this happens?

Try fliping only those faces, not all.

Instead of just flipping all the normals, re-calculate them all (ctrl + N)

I have had a very hard time fixing a broken model before, the best advice I can give, is to check your render with a “grid” texture now and then, and try and see when you go wrong and how, sometimes decimate does this to me, sometimes I “split” a model, and then fix that half, and then mirror, and do remove doubles

I believe in the properties panel (press the N key in the 3D view), under the display options, you can enable backface culling for the viewport. Not sure if you need to be in solid mode for this to work, but it should make it more obvious which faces you need to fix without constantly restarting the game engine.

Definitely looks like a problem with normals. Hint for fixing: go to your 3d viewport of your model. Go to edit mode, press ‘n’ key to bring up a side menu, scroll down to ‘Mesh Display’ dropdown, there’s a ‘normals’ subheading, click ‘display face normals as lines’. This will allow you to at a glance see which normals are pointing the wrong way. Now, when you’ve found the normals that are facing the wrong way, press ‘t’ key to open another side menu and you’re looking for ‘Mesh tools’ dropdown. There’s a subheading called ‘normals’ once again, and you’re looking for the button called ‘flip direction’

Thanks for the help guys. I tried everything, but eventually I figured it out. I needed to recalculate then flip normals. ( It wouldn’t do it for any other combination, don’t know why)