Canvas editor

How selection works across the GCS, ACS, and LGS canvas editors — one-step selection, additive multi-selection, vertex handle dots, and clearing.

Overview

All three design tools — GCS (General Cross Section), ACS (Advanced Concrete Section), and LGS (Light Gauge Steel) — share the same canvas editor interaction model for selecting geometry. This page covers how selection works; for pan and zoom, see Canvas navigation.

One-step selection

This page describes the Select tool. While a placement or drawing tool is active instead — placing a bar in ACS, or drawing an outline with Draw Polygon or Draw Arc — a canvas click performs that tool’s action rather than changing the selection.

Clicking a vertex, edge, or an arc’s centre handle immediately selects it. There is no prior hover or focus step — the item is selected on the first click.

This is consistent across all tools and modes. Whether you are using the Select tool in ACS, picking geometry in GCS, or clicking nodes in LGS, a single click always produces a selection without any intermediate step.

Plain click — single selection

A plain click (no modifier key) selects one item and replaces any previous selection:

Shift-click — additive multi-selection

Hold Shift while clicking to extend the current selection:

• Shift-click a vertex — adds it to the selection without removing existing items.
• Shift-click an edge — adds that edge.
• Shift-click an arc centre handle — adds it, treated the same as a vertex.

The accumulated selection grows until you click the canvas background (clear) or perform an action that consumes it (such as applying a constraint).

Additive multi-selection is required for constraint authoring in ACS and GCS, where you assemble a combination of vertices and edges before the constraint action bar appears.

Outline stroke weight

Section outlines are drawn at 2 px (pre-zoom). When a vertex or edge on an outline is selected the stroke steps up to 3 px to reinforce the active state. Both weights scale inversely with zoom so the outline reads at a consistent visual thickness regardless of how far in or out you are.

Vertex handle dots

Vertex handles — the small circular dot markers at each outline or polygon vertex — are hidden by default to keep the canvas uncluttered. They are revealed when any of the following is true:

• The mouse is hovering over the outline or polygon.
• A vertex, edge, or an arc centre is currently selected (single-selection or multi-selection).

This means once you have clicked to select something, the handles stay visible until you clear the selection, making it easy to Shift-click additional vertices without moving the mouse back over the outline first.

The handles remain in the canvas at opacity zero when hidden. This means you can click or drag a vertex without hovering first — the grab registers immediately, and the dot appears as you move.

Arc centres are a cross, not a dot. Every arc edge — in ACS on the outline or a freeform void, in GCS on any element — also carries a centre handle, rendered as a small upright cross off the ring itself (never on it, since the centre is not a ring point). The different shape is deliberate: colour alone never distinguishes a selection state on this platform, so the centre needs a non-colour cue that separates it from a ring vertex at a glance. A cross is open geometry, so it stays unmistakable against a round vertex dot at any zoom — and it is the same mark the platform already uses for a centre, as in the centroid and shear-centre crosses on the LGS canvas, and the same centre mark used in drafting practice. Unlike a vertex, a centre has no drag — it is selection-only — so it is hidden (not merely dimmed) and un-clickable whenever hover/selection state would hide it, rather than sitting invisibly clickable the way a draggable vertex handle does.

Clearing the selection

Click anywhere on the canvas background (empty space, not on a vertex, edge, or an arc centre handle) to clear both single-selection and the accumulated multi-selection set. Because a hidden centre handle stops accepting clicks entirely, an arc centre that is currently out of view can never swallow a background click meant to clear the selection.

Keyboard shortcuts

The tool palette on each canvas surface labels every tool button with its keyboard shortcut. Pressing the key activates that tool immediately — no click required.

On macOS, use ⌘ in place of Ctrl for undo and redo. Shortcuts fire whenever the keyboard is not captured by a text input, an open dropdown, or a dialog. The Alt and Meta modifiers are excluded — those belong to browser bindings.

Tool palette overflow

When the canvas centre slot is too narrow to display every tool button at once, surplus tools move into a ⋯ (More tools) dropdown at the right end of the palette rather than wrapping or scrolling. The dropdown opens above the palette and shows each tool’s icon, name, and keyboard shortcut (where one exists).

Two items are always visible regardless of how narrow the canvas gets:

• Select (the first tool in the first group) is pinned and never overflows.
• The currently active tool is always pinned — overflowing the active tool would leave the canvas in a mode with no visible indication of which one.

Keyboard shortcuts continue to work for overflowed tools. The shortcut bindings are held independently of what is on screen, so pressing P (Draw Polygon) or A (Draw Arc) in ACS still activates those tools even when their buttons have moved into the menu.

ACS specifically. ACS has nine palette tools, five of which declare no keyboard shortcut: Edge Pattern, Perimeter Pattern, Individual Bar, Bar Wrap, and Cell Tie. On a narrow canvas — for example, with the left panel wide open, or on a small screen — these may be the first to move into the overflow menu. If you cannot find a tool button, click the ⋯ trigger to reveal it.

Related pages

• Canvas navigation — pan, zoom, status bar, and fit controls.
• Constraint creation — using multi-selection to author geometric constraints in ACS.
• Parametric sketcher — managing constraints, the status chip, and the Constraint List Panel.