View source for Smoothing groups

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[[File:Smoothing groups smoothing example.jpg|thumb|400px|right|The cylinder on the left is not smoothed.<br> The cylinder in the middle is smoothed with the default [[Lightmap#Scale|lightmap scale]] of 16.<br> The cylinder on the right is smoothed with a [[Lightmap#Scale|lightmap scale]] of 8.]]

'''Vertex Smoothing''' simply uses [[Vertex normal]]s ([[vector]]s) as if they were [http://en.wikipedia.org/wiki/Surface_normal Surface normals] to generate a kind of ''pseudo-''[http://en.wikipedia.org/wiki/Subdivision_surface subdivision surface] for the Lighting shader to work with. This is also known as {{w|phong shading}}, not to be confused [[phong materials|phong reflections]].

When a number of adjacent surfaces are assigned to the same [[Smoothing group]], the ''Rendering Engine'' will "soften" the light and shadow across each vertex or edge shared by the group. This makes the geometry seem smoother when viewed from most angles. It does not soften the profile or silhouette of the object.

{{tip|On lightmapped surfaces, smooth shading will be more effective on higher-resolution lightmaps; see right.}}
{{tip|Edges sometimes must have contiguous texture [[UV]]s for smooth shading to have a noticeable effect, particularly on vertex-lit geometry.}}
{{bug|In {{src13|4}} and possibly other engine branches, [[smoothing groups]] are not properly written for [[func_detail|detail brush]] faces. This is fixed in the {{slammin|2}}, {{mapbase|2}}, and {{gmod|2}} versions of VBSP, and code for this fix can be found in [https://github.com/ValveSoftware/source-sdk-2013/pull/391 pull request 391 on GitHub].
{{workaround|If stock compilers must be used, increasing the auto-smoothing threshold to 47 ({{code|-smooth 47}}) can help. Alternatively, use [[func_brush]].}}}}
{{modernImportant|Hammer's smoothing groups only affect [[brush]]es, not [[displacement]]s! Displacements which are sewn together are always shaded smooth; this can be worked around by having the vertices of the base brush faces not be aligned, manually aligning the displacement vertices together instead of sewing.}}

==Guidelines==
* Brush geometry must be manually assigned to a Smoothing Group in Hammer. Model geometry smoothing data is configured in the [[model editor]] before [[SMD export]].

==Auto Smoothing==
* In at least some games, VRAD will auto smooth angles (between faces without smoothing groups) which are less than or equal to the {{code|-smooth}} parameter (default 45).
{{modernConfirm|When was this added? {{src13}} and {{csgobranch}} have this, but {{src07}} does not.}}
[[File:AutoSmoothing.png|thumb|600px|left|Brushes of 45 degrees or less will be auto smoothed.]]{{clr}}

==See also==
* [[Hammer_Smoothing_Groups_Dialog|Smoothing Groups in Hammer]]
* [[Model_Creation_Overview#Editing_Hard.2FSoft_Edges|Smoothing Groups in XSI]]
[[Category:Modeling]][[Category:Level Design]]