Per Pixel Lighting

[dainja556]

I'm just curious what "Per Pixel Lighting" affects.  I toggle it, but can't notice any difference.

Would someone mind explaining what that option does?  It does seem to make a noticeable impact on my framerate.

I found this post: http://www.x-plane.com/blog/2009/05/per-pixel-lighting-isnt-free/

It talks about per pixel lighting, but I'm still not certain what visual difference it makes.

[Jack Skieczius]

Let me try and sum this up for you.

Per pixel lighting, and vertex lighting, are the two ways to light a 3d object. That is being very basic of course, but for this explanation that will do.

When you have per-pixel lighting turned on, each pixel on your screen, is being sampled for lighting. This means the rendering engine has to draw a ray or line from the camera to the pixel then to the light and figure out the angle of the polygon to the light, and then return a value which gives you your shading. Today most computers have no problem rendering per pixel lighting what soever, but back 10 years ago, that wasn't so.

Back then the standard was vertex lighting which only samples light from the vertexes, or points that make of the polygon mesh inside the 3d space. the lighting sampled is then shaded over the polygons like a gradient. Vertex lighting is very fast for this reason but offten it wont look as good, infact most of the time it will look rather horible unless the mesh you are looking at has a large number of vertexes in it.

Take a look at this wiki page to see a visual exsample of what vertex lighting looks like: http://en.wikipedia.org/wiki/Gouraud_shading

hope that helped.

[dainja556]

Yea, that's a very good explanation.  Thanks!

Does X-Plane use vertex shading by default (when per-pixel is disabled), or does it use something else?

I was having a hard time telling the difference between the default and the per-pixel, perhaps that's because I was using a high-poly aircraft.

[-TheoGregory]

To see normals maps applied on an aircraft, you need to have per pixel lighting on. And we all know how cool normal maps are

[dpny]

Fly over water with per-pixel on, and then off. You will notice an enormous difference.