There are a lot of inaccuracies in the article. > "Rasterization starts with a particular pixel and asks, 'What color should this pixel be?' " Nope. Traditio

There are a lot of inaccuracies in the article. > "Rasterization starts with a particular pixel and asks, 'What color should this pixel be?' " Nope. Traditional polygon rasterization just works its way through a drawlist and rasterizes each polygon into a frame buffer (checking against a depth buffer so that things far away don't get drawn in front of things that are nearer). It's only at the end of the drawing process that we can inquire what color a particular pixel is. > "Ray tracing works from the viewing angle and light sources and asks, 'What is the light doing?'" No, ray tracing traces rays out from the eye and figures out what they hit. Path tracing traces rays out from the eye and samples a bunch of random rays when they hit something, to simulate global illumination, soft shadows, and similar effects. Photon mapping literally simulates photons by tracing rays randomly out from the light sources and depositing their hit locations in a data structure. (That's probably the most literal match for the description of figuring out "what the light is doing".) > "Ray tracing works by tracing the path of a light ray as it bounces around a scene. Each time a ray bounces, it mimics real-life light by depositing color from earlier objects it has struck, and also loses intensity. This depositing of color makes the sharp reflections and subtle, realistic color variations that, for certain types of materials and effects, can only be achieved with ray tracing." This is a pretty accurate description of photon mapping. Ray tracing and path tracing work in reverse, by tracing rays from the eye. Since path tracing and photon mapping fundamentally work by tracing rays (i.e. doing ray-intersection tests between rays and objects), it's not completely unreasonable to refer to a path tracer or photon mapping renderer as a ray tracer, but not all ray tracers work the way the article describes. > "Because it mimics light’s real behavior, ray tracing also excels at producing area shadows and ambient occlusion. " You can do area shadows and ambient occlusion in a ray tracer if you're willing to do a lot of random ray sampling, but it's not inherently a characteristic of ray tracing. > "Until now, ray tracing was implemented only in offline rendering due to its intense computational demands. Scenes computed with ray tracing can take many minutes to hours to compute a single frame, twenty-four of which are needed to fill a single second of a film animation." This may be an accurate description of path tracing with enough samples to drive the noise down to a level that's imperceptible, but ordinary ray tracing of non-pathological scenes doesn't usually take that long these days on modern hardware. People have been doing real-time interactive ray tracing for a long time (I recall running Outbound on a Core2 duo laptop about 10 years ago. Framerate was choppy and resolution wasn't great, but it worked). Brigade is a more recent real-time path-tracing rendering engine, and it's been around for years as well. That isn't to say that their demo isn't an impressive technical achievement.