UGTK / Toolkit / Libraries Extensions / AnchorsLibrary Completed

Anchor Library

Summary

The Anchor Library sets a RectTransform's anchors from a preset, in one call — the thing Unity only lets you do by hand in the inspector's anchor popup. It is what you need when the layout is decided at runtime: an element that must stick to the top-left on one screen and to the bottom-center on another.

The important part: it preserves the on-screen position and size. Changing anchors by hand normally makes the element jump; here the previous anchoredPosition, sizeDelta and pivot are read first and restored after, so only the anchoring behaviour changes, not the look.

Content

• Modules Dependencies
• Setup
• How To Use
• Testing Scene
• Technical Info

Modules Dependencies

None. A single static extension class, no UGTK reference.

Setup

Nothing to set up: no component, no prefab. Add UGTK.LibrariesExtensions.AnchorsLibrary to your assembly definition references and call the extension method on any RectTransform.

How To Use

targetRectTransform.SetAnchor(E_AnchorPosition.TopLeft);
targetRectTransform.SetAnchor(E_AnchorPosition.MiddleCenter);
targetRectTransform.SetAnchor(E_AnchorPosition.MatchRectTransform);

The presets — the nine classic positions plus one special value:

MatchRectTransform is the "stretch" case: the anchors are collapsed onto the element's current rectangle, so from then on the element scales with its parent instead of keeping a fixed size. It is the programmatic version of Unity's alt+click stretch preset.

Good to know:

• Position and size are preserved, the behaviour is not. After the call the element looks identical but reacts differently to a parent resize — that is the whole point, and also the thing that surprises people.
• A null RectTransform logs an error and returns: no exception, so a wrong reference shows up in the console rather than as a crash.
• It works on the RectTransform, not on the layout. Inside a LayoutGroup the group owns the anchors and will overwrite them at the next rebuild.

Testing Scene

Open Debug/AnchorsLibraryTest.unity. A white square sits in the middle of the canvas, a panel of ten buttons sits bottom right, and AnchorTest carries Mn_AnchorLibraryTest, which is wired to both. Select AnchorTest and right-click the component header: the same presets the buttons apply in play mode are there as context menu entries, so the whole set can be walked with the editor stopped.

What to do, in order:

1. Run Apply preset once. The Output box reports the preset, the two anchors, the size, and how far the element moved.
2. Run Next preset nine times to walk the whole enum.
3. Watch the last line of the report at every step: moved 0 px, resized 0 px.
4. Press Play and use the on-screen buttons instead. They call exactly the same method.
5. Resize the Game view. Now the presets differ: an element anchored to a corner keeps its size and stays glued to that corner, while MatchRectTransform grows and shrinks with the parent.

Step 3 is the whole point. Setting the anchors on their own moves the element, because anchoredPosition and the offsets are measured from the anchor - and the anchor has just moved. The utility measures the rect against the parent first and writes it back afterwards, which is what Unity's own anchor preset widget does.

MatchRectTransform is the odd one out: it turns the element's current rect into anchors and drops the offsets, so it stays exactly where it is and starts scaling with its parent. In the report you can see it as a pair of fractional anchors, (0.47, 0.45) and (0.53, 0.55), instead of a corner.

Technical Info

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© 2026 Marcello De Bonis. All rights reserved

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