Cooking is the term used for computing or calculating the operators of networks. Middle-click on a node to see how long it last cooked, and how many times it cooked since you started TouchDesigner.
TouchDesigner will cook a node only when it needs to - it doesn't cook every node every frame.
When you see the wires between nodes animating, it means the upstream node is cooking, the downstream node(s) may or may not be cooking.
Dialogs -> Performance Monitor will show you what has cooked in one frame. Making your synth run at 30 or 60 frames per second involves minimizing the number of nodes that cook.
What Causes Cooking
For a node to cook two things need to be true. The node needs to have a cook request (something asking it to cook), and it needs to have a reason to cook.
Things that cause a cook request:
- A node connected to that node's output wants to cook.
- A node referencing that node via a parameter wants to cook.
- A viewer is looking at the node's data.
- The opcook Command.
Things that give a node a reason to cook.
- One of that node's inputs has cooked.
- A node it points to via a parameter has cooked.
- One of the node's parameters change.
- Specific scripting commands are run on the node.
- The result of an expression may have changed.
- A variable the node refers to changes values.
- A node that one of its parameter's expressions points to has cooked.
- The node is time dependent, that is to say each frame it can output different data, even if none of its inputs or parameters change (like the Time Slice CHOP).
- A user interacts with it, but only if it is a Panel Component.
When a node receives a cook request, it requests that all of its inputs cook, which may or may not cause them to cook. If any of them cook, then it has been given a reason to cook, and it'll cook. If none of them cook then it'll check for other possible reasons to cook. If none of those are present, it won't cook (and you won't see it in the Performance Monitor).
For example, if you are looking at the viewer for a default Constant CHOP (one channel with no expressions), that node is constantly getting cook requests (every time the UI redraws for example), but it never cooks, because it has no reason to cook.
The Order of Cooking
TouchDesigner is a "pull system". A common misconception with cooking in TouchDesigner is that cooking starts upstream and moves downstream. For example if you have Constant CHOP connected to a Math CHOP, most people assume if you change a value in the Constant CHOP then the Math CHOP is forced to cook. This is incorrect. Almost all operators will only cook when something is interested in their data. What this means in our example is that while changing a parameter in the Constant CHOP will make it 'dirty', it won't cook until someone asks for its data. So the Constant CHOP won't cook until the Math CHOP asks for its data. The Constant CHOP may cook for other reasons, like if its viewer is on (ie. the user is asking to see its data).
Some nodes, specifically nodes like the Movie Out TOP, Touch Out OPs and other *Out OPs will cook every frame, regardless of any of their inputs or parameters changing. This behavior ensures that the recipient of their output (a movie, a network pipe, etc.) gets a continuous stream of data.
Other nodes, if asked to cook, will cook even if none of their inputs or parameters have changed. These are mainly special nodes like the Render TOP, and *In OPs (like the Touch In and Pipe In CHOPs, but not In CHOPs and In SOPs). The nodes have so many possible input changes to monitor (for the Render TOP: materials, geometry position, geometry render flags, etc.) that instead of trying to figure out if they should cook, they just do. Always cooking saves computation cycles 99% of the time for these nodes, as most of the time something is changing in the rendered scene.
See also: Null CHOP