# "Synchronize" Backface Culling
**URL:** https://discussions.unity.com/t/synchronize-backface-culling/652627
**Category:** Graphics
**Created:** [January 19, 2017, 10:02pm UTC](https://discussions.unity.com/t/synchronize-backface-culling/652627 "2017-01-19T22:02:10Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@mbue](https://discussions.unity.com/u/mbue)
#### Post date: [January 19, 2017, 10:02pm UTC](https://discussions.unity.com/t/synchronize-backface-culling/652627/1 "2017-01-19T22:02:10Z")
I got a quad primitive which some objects in front of it. The quad represents some kind of wall. I want the wall to be visible from one side only, back face culling comes in handy here. 😉
However, as soon as the quad is backface culled, the objects infront of the quad should disappear.
So I’d need something like (Pseudocode):
```csharp
objects.visible = !wall.backfaceCulled
```
I got it working for orthographic projection by going through a manual culling process:
- I calculate the normal of the triangle of the quad
- I use the dot product of that normal with the camera direction and check whether its \> 0.
- If \< 0, the renderer ob the objects in front of the wall are disabled.
It works fine with orthographic projection, however I’m missing something regarding perspective:
The normal of the quad would need to be “distorted” by the projection view as in the following picture:
Yellow shows the calculated normal. If it would follow the blue line, the culling should work fine.
```csharp
// filter is the MeshFilter of my quad
var v0 = filter.mesh.vertices[0];
var v1 = filter.mesh.vertices[1];
var v2 = filter.mesh.vertices[3];
// Local space to world space
var v0World = visibilityParent.transform.TransformPoint(v0);
var v1World = visibilityParent.transform.TransformPoint(v1);
var v2World = visibilityParent.transform.TransformPoint(v2);
// Calc normal
var sideVec1 = v1World - v0World;
var sideVec2 = v2World - v0World;
var normal = Vector3.Cross(sideVec1, sideVec2);
normal.Normalize();
var visible = Vector3.Dot(normal, Camera.main.transform.forward) > 0;
```
Any ideas?
Thank you in advance.
---
### Author:  [@bgolus](https://discussions.unity.com/u/bgolus)
#### Post date: [January 21, 2017, 12:34am UTC](https://discussions.unity.com/t/synchronize-backface-culling/652627/2 "2017-01-21T00:34:23Z")
There’s not really a need to calculate the normal. Assuming you’re using the default quad you can just use [transform.forward](https://docs.unity3d.com/ScriptReference/Transform-forward.html) to get the normal direction (actually going to be -transform.forward). Then for the dot product you want use the world space relative vector from the camera to the quad’s transform rather than camera forward, assuming you’re using a perspective camera and not orthographic.
`var visible = Vector3.Dot(-transform.forward, transform.position - Camera.main.transform.position) > 0.0f;`
That might be backwards.
---
### Author:  [@mbue](https://discussions.unity.com/u/mbue)
#### Post date: [January 23, 2017, 11:11am UTC](https://discussions.unity.com/t/synchronize-backface-culling/652627/3 "2017-01-23T11:11:52Z")
Thank you really much, it works.
I really overcomplicated this. 🙂