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books/free-programming-books-subjects.md

@@ -316,9 +316,13 @@ Books that cover a specific programming language can be found in the  [BY PROGRA
 * [Learning Modern 3D Graphics Programming](https://web.archive.org/web/20150225192611/http://www.arcsynthesis.org/gltut/index.html) - Jason L. McKesson (draft)
 * [Notes for a Computer Graphics Programming Course](https://www.cs.csustan.edu/~rsc/CS3600F00/Notes.pdf) - Dr. Steve Cunningham (PDF)
 * [OpenGL](http://www.songho.ca/opengl/index.html) - Concepts and illustrations
+* [Physically Based Rendering, Third Edition: from Theory to Implementation](https://www.pbr-book.org) - Matt Pharr, Wenzel Jakob, Greg Humphreys
+* [Ray Tracing Gems](https://www.realtimerendering.com/raytracinggems/rtg/index.html) - Eric Haines, Tomas Akenine-Möller
+* [Ray Tracing Gems II](https://www.realtimerendering.com/raytracinggems/rtg2/index.html) - Adam Marrs, Peter Shirley, Ingo Wald
 * [Ray Tracing in One Weekend](https://raytracing.github.io) - Peter Shirley (HTML)
 * [ShaderX series](http://www.realtimerendering.com/resources/shaderx/) - Wolfgang Engel
 * [Tutorials for modern OpenGL](http://www.opengl-tutorial.org)
+* [Virtual Reality](http://lavalle.pl/vr/) - Steven M. LaValle
 * [WebGL Insights](http://webglinsights.com) - Patrick Cozzi, et al.