Core concepts

• POP: TouchDesigner's point operator family. A POP holds points and primitives (such as triangles) with attributes such as P (position), N (normal), Cd (colour), v (velocity) and pscale (size). All HRLW solvers speak POP: you steer them with points, and they output points or meshes.
• TOP: TouchDesigner's texture operator family. The path tracer outputs an image, so it is a TOP.
• Info CHOP: right-click an operator and add its Info CHOP to read counters and timings. Channels are listed per chapter and in Appendix B.
• Path tracing: the renderer shoots rays from the camera, bounces them off surfaces and collects light. Shadows, reflections, glass and smoke come out of the physics instead of tricks, at the cost of noise that the denoiser removes. When the camera is still, the image accumulates and gets cleaner; moving anything restarts or reprojects it.
• Solver: the part that moves things each frame (liquid, smoke, bodies).
• Parameter names. Tables give the label as it appears in TouchDesigner. The scripting name (what you type in Python, op('liquid1').par.Maxsubsteps) is the label's words run together, first letter capitalised and the rest lower case (Smoke Weight is Smokeweight, Output to TouchDesigner is Tdoutput). Hover over a parameter or list op('x').pars() to see it. Text in brackets in a label is a hint, not part of the name.
• Greyed-out parameters. A parameter is greyed out when it currently has no effect: the input it needs isn't wired, or another setting turns it off. TouchDesigner's C++ operators can grey parameters out but not hide them.
• Sections in each chapter: Replaces, Quick start, Attributes, Parameters, Advanced.