Tutorial for shadow mapping: http://www.paulsprojects.net/tutorials/smt/smt.html
Resources about shadow techniques:
- generalities: http://www.peroxide.dk/papers/realtimesoftshadows.pdf
- generalities: Algorithms for Real-Time Rendering of Soft Shadows – http://www.csse.canterbury.ac.nz/research/reports/HonsReps/2007/hons_0705.pdf
- listing: http://www.nvidia.com/object/doc_shadows.html
- cascade shadow map: http://developer.download.nvidia.com/SDK/10.5/opengl/src/cascaded_shadow_maps/doc/cascaded_shadow_maps.pdf
- volume lights: http://developer.download.nvidia.com/SDK/10.5/direct3d/Source/VolumeLight/doc/VolumeLight.pdf
- percentage closer soft shadows:
- http://developer.download.nvidia.com/SDK/10.5/direct3d/Source/PercentageCloserSoftShadows/doc/PercentageCloserSoftShadows.pdf
- http://developer.download.nvidia.com/shaderlibrary/docs/shadow_PCSS.pdf
- variance shadow mapping: http://developer.download.nvidia.com/SDK/10.5/direct3d/Source/VarianceShadowMapping/Doc/VarianceShadowMapping.pdf
- Opacity Shadow Maps in Crystal Space, tagged PSSM: https://volumetricshadows.wordpress.com/tag/pssm/
- stencil vs pssm: http://www.conitec.net/beta/shadows_c.htm