Features and the timeline

A design in Extrudo is a list of steps, not a lump of geometry. Each step is a feature: a sketch, an extrude, a fillet, a hole. The list is the timeline, along the bottom of the window. The model is what you get by running the steps in order, which is why you can go back, change one and watch the rest follow.

What a feature is

A feature is a tool you ran, with the choices you made: which profile, how far, which edges. Extrudo keeps those choices, not the shape. When you change one, it runs the steps again. That is why a number you edit in step 2 can move a fillet made in step 7.

Each feature is a chip on the timeline, coloured by kind and named after what it is: Sketch1, Extrude1, Fillet1.

The dialog pattern

Nearly every feature tool opens the same kind of dialog, a floating panel at the top right of the view. You can drag it by its title. Nothing is committed until you press OK.

• Pick fields are buttons: Profiles, Faces, Edges, Axis. The one that takes your clicks has an amber outline. Click in the view to add or remove an item, or drag a box. Only what the field accepts lights up. Select things before you choose the tool and the dialog opens with them filled in.
• Expression fields take a number, a unit or an expression: 20, 20 mm, wall * 2.
• Handles in the view do the same job as the fields: an arrow for a distance, an arc for an angle. Drag one, or type straight into the value box beside it. The field follows.
• A live preview shows the result as you change things. New material is tinted blue, a cut is red, and a join is green. If a value can't work, the field shows the message under it and the preview stays on the last good result, dimmed.
• OK commits one undo step and adds the chip. Cancel, or Esc, closes the dialog and changes nothing.

Some tools also have a key (E for Extrude, F for Fillet, H for Hole). Press Q for Press Pull, which opens whichever dialog fits what you selected: a profile extrudes, a face offsets and an edge fillets.

New body, join, cut

Extrude and Revolve have an Operation: New body, Join, Cut or Intersect. You usually don't have to set it. Extrudo proposes one from where the profile is: a profile out in the open makes a new body, one on a face that grows outwards joins that body, and one that goes into the material cuts it. Change it if the guess is wrong.

Each solid is its own body, listed in the browser. If a cut splits a part in two, you get two bodies, and the larger keeps the name and colour.

Editing a feature

Double-click its chip, or right-click it and choose Edit Feature. The dialog opens with the feature's choices. While you edit, the timeline marker shows dashed after the chip and later chips dim, and the model in the view is what the feature would give. OK applies it, and every step after it runs again.

Double-clicking a sketch chip opens the sketch instead.

The timeline

The marker is the amber bar between chips. Features before it are in the model, and features after it are dimmed and not computed. Drag the marker to roll the model back. Focus it and use the arrow keys, Home and End, or use the playback buttons at the left (roll back to start, step back, step forward, roll forward to end). Right-click a chip and choose Roll Back to Here to put the marker just after it.

New features always go in at the marker. Roll back, add a feature, and it lands in the middle of the history, with the later ones recomputed on top. Moving the marker is one undo step.

Reordering. Drag a chip to move it; a line shows where it will land. The line turns red, with the reason, if the move would put a feature before something it uses. A fillet can't move before the extrude that made its edges. Dropping there tells you why in a message, and Esc puts the chip back. Click one chip and Shift-click another to pick a run, and drag any of them to move the lot. Move to End in the menu does the same without dragging.

Suppress and hide. Suppress turns a feature off without deleting it: its chip dims and the model is computed without it. Choose it again to bring it back. Hide hides a sketch's curves in the view without changing the model; its menu is only on the features whose drawn geometry hiding changes (sketches, construction geometry, canvases — a body is hidden with its eye in the browser). Delete removes a feature, but refuses while a later one uses it, and tells you which.

Groups. Pick a run of neighbouring chips, right-click, and choose Group 3 features. A group folds into one chip with a count. Open it with the arrow beside it. F2 renames it, and its menu has Ungroup, Hide and Suppress for the lot. Groups are only for tidiness: they don't change what is computed.

When a reference is lost

A fillet remembers which edge it rounds. If you change an earlier step so that the edge is gone, the fillet can't do its job. Extrudo tells you in three places: the chip gets a ✕ (or a ⚠ when it could carry on, for instance with a reference it had to guess), the status bar counts the errors, and the notification history (the bell at the right end of the status bar) lists them. Hover the chip for the message.

For a ⚠, the chip's menu has Keep Closest Match, which accepts the edge Extrudo picked and stops warning. For a ✕, choose Fix References…: the feature's dialog opens with the lost picks removed and the field waiting for a new one. For a sketch it is Redefine Plane, which asks for a new plane or face.

While you hover the chip, or while Fix References is open, the lost geometry is drawn as a dashed red ghost where it used to be, so you can see what it was and pick its replacement.

Why a name survives an edit

Extrudo doesn't remember a face as "face number 7", because numbers shift whenever something before it changes. It remembers a face by how it came to be: "the end cap of Extrude1" or "the side made by that line of Sketch1". Change the sketch, move the extrude's distance or add a feature in between and that description still finds the same face. When it can't find an exact match it looks for the face most like the one you picked, and warns you so you can accept or fix it. Only when nothing is close does the feature fail.