constrain

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Modeling - Drawing

Constraining creation with Shift

Holding Shift while placing a point locks it to an axis or forces a true square, with a dotted guide showing the lock.

When you're placing points to build a shape, you often want the next point to land squarely - straight across, straight up, or at a clean right angle from the last one. Holding Shift while you place that point does exactly this: it snaps the point into a constrained position instead of letting it fall wherever the cursor is.

What Shift locks

The constraint is always relative to the previous pending point - the last point you set in the shape you're currently drawing. Shift measures from there, not from the origin or the grid as a whole.

For most tools, holding Shift locks the new point to an axis relative to that previous point. Locus looks at how far you've moved horizontally versus vertically and keeps only the larger direction, zeroing the smaller one - so the point lands on a clean horizontal or vertical line from where you started. This is the placement-time version of the axis lock you get when dragging an existing point with Shift held.

The XY-aligned rectangle is the special case. Holding Shift while you place its second corner forces a true square - it makes the width and height equal (keeping the direction you dragged), so you get a perfect square from the first corner without switching tools. This is the same square you'd otherwise build with the dedicated square tool.

The dotted guide

While the constraint is active, Locus draws a soft dotted guide line from the anchor point through your locked cursor position. It's there so you can see the lock as it happens - and see which axis it caught - before you commit the click. The rubber-band preview of the shape follows the same constraint, so what you see while hovering is what you'll get when you release.

The locked line also finds the geometry it runs into. When it crosses a segment, circle, arc, line or ray near the cursor, the hover shows the crossing marker there and the click lands exactly on that crossing - so a Shift-vertical segment ends on the line it meets, not a hair short of it or past it. The square lock on the XY-aligned rectangle doesn't do this; its corner stays wherever the square puts it.

Which tools it affects

Shift-constrained placement applies to the multi-click tools that drop a free point on a later click - the ones where the next point could go anywhere and a lock is meaningful. That includes segments, lines through points, rays, circles, three-point circles, arcs, ellipses and elliptical arcs, the aligned rectangle (as a square), squares, midpoints, divide, perpendicular bisectors, and the angle bisector in its point mode.

The plain Point tool honors Shift too, but relative to the currently selected point rather than a pending one: with a point selected, hold Shift as you drop the next point and it axis-locks to that selection - the same dotted guide, drawn over the crosshair.

The directed rectangle is a partial case: Shift locks only its second corner. Its third click sets the rectangle's width - a perpendicular distance - which is deliberately left free so you can size it however you like.

Note

Tools that don't place a free point relative to another - select, glider, the radius-value circle, perpendicular, parallel, tangent, and intersection - don't respond to Shift. There's nothing for the constraint to lock, so holding Shift simply does nothing with them.

For the related square shortcut and the tools it ties into, see Rectangles & squares.

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