Darkplaces lighting

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Darkplaces engine uses combined lighting model. Several lighting methods are implemented to give best results at cases they are aimed for.

Light models

Darkplaces using several lighting models, most of them are set globally:

• Phong lighting model - generic and default lighting model
• Fake light - a developer-only mode which is forced on non-lit maps (ones which was compiled and didnt get LIGHT phase). This is infinite realtime light that is cast from eye position.
• Cel shading - a phong lighting model with altered shading.
• Fullbright - no lighting applied

Light methods and effects

There is 4 lighting methods used in Darkplaces:

• Vertex lighting - static lighting, aimed at big counts of simple surfaces
• Lightmaps - static lighting, aimed at surfaces that receives shadows from static objects
• Lightgrid - static lighting, aimed at moving entities
• Realtime lighting - full dynamic lighting (each light is a separate pass), aimed at switchable and moving lightsources that lights moving entities

Additionaly, Darkplaces supports a number of lighting effects:

• Coronas - aimed to simulate glow around lights, which looks good on small and medium size lights
• Planar shadows - each entity cast one shadow on the floor (or by global vector)
• Customized modellight - lightgrid-sampled model lighting could be replaced with QuakeC
• Fog - global fog and global volumeric fog (with height set) are suppored

Shadow mapping vs Stencil shadows

Stencil shadow volumes is a shadow rendering method Darkplaces used in pre-2010. Since 2010 shadow mapping was implemented by Eihrul.

Shadowmapping have a number of advantages over shadow volume rendering and is considered to replace it:

• It is faster to render (especially on complex area maps)
• Takes less CPU time (as construction of shadow volumes is not required)
• Distance-based LOD (far lights rendered with lower shadowmap resolution)
• Shadow edges are not sharp

Comparison of different lighting methods

Task	Vertex lighting	Lightmap	Lightgrid	Realtime lighting
Details	Low	Medium	Low	High
Render speed	Fastest	Fast	Fastest	Slow
Precomputation time	Short	Long	Medium	N/A
RAM usage	Low	High	Low	Low
Shadows	No	Yes	No	Yes
Penumbra	N/A	Yes	N/A	Partial
Number of lights	Large	Large	Large	Small
Surface-based effects
Bumpmapping	Yes	Yes	Yes	Yes
Specular	Yes	Yes	Yes	Yes
Cubemap filters	No	Partial	No	Yes
Per-light diffuse/ambient/specular scale	No	No	No	Yes
Non-point 'area' lights	Yes	Yes	Yes	No
Light styles	No	No	No	Yes
Moving lights	No	No	No	Yes
Global illumination
Precomputation time	Long	Very long	Long	N/A
Rendering speed	N/A	N/A	N/A	Slow
Quality	High	High	High	Low
Used to light
Map surfaces	Yes	Yes	No	Yes
Static BModels	Yes	Yes	Optional	Yes
Moving/rotating BModels	No	No	Optional	Yes
Animated models	No	No	Yes	Yes

Console variables

 r_shadow_realtime_world : Enabled realtime lighting of world lights (stored in external .rtlights file)

 r_shadow_realtime_dlight : Enabled realtime lighting of dynamic lights (created by entities)

 r_shadow_* : A group of cvars to control realtime lighting

 r_shadow_shadowmapping : Enables shadowmapping which replaces default shadow volume-based lighting

 r_shadow_shadowmapping_* : A group of cvars to control shadowmapping

 r_shadows_* : A group of cvars to control planar shadows

 r_showlighting : Show areas lit by dynamic lightsources. Useful for finding out why some areas of the map render slowly (bright orange = lots of passes, slow)

 r_showshadows : Show areas covered by shadow volumes. Useful for finding out why some areas of the map render slowly (bright blue = lots of passes, slow). Only matters if using shadow volumes.