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Mirror Symmetry

Mirror Symmetry lets you build symmetric structures in half the time: you do the work on one side of the axis, and Buildopia automatically duplicates every action on the other side. This guide covers how to turn it on, what it affects, and how to use it most effectively.

The Mirror Buttons

Two buttons in the sidebar (and in the top bar during building) control mirroring:

You can enable either axis on its own for a two-sided build, or enable both at once for a full four-way mirror. When both are active, a single block placement near one corner of the grid creates matching blocks at all four corners simultaneously.

Mirror Plane Visuals

When Mirror X or Mirror Z is active, a semi-transparent plane appears in the 3D viewport to show you exactly where the mirror axis sits:

• Mirror X — a blue semi-transparent plane running the full height and length of the grid, centred on the X axis.
• Mirror Z — an orange semi-transparent plane running the full height and width of the grid, centred on the Z axis.

When both axes are on, both planes are visible simultaneously, forming a cross through the centre of the grid. The planes update as you resize the grid, so they always span the exact boundaries of your build.

These visuals make it much easier to judge which side of the axis you're placing on and to spot when a block lands exactly on the centre line — which places only one copy rather than a mirrored pair. The planes don't affect rendering or export; they're editor-only guides.

What Mirror Affects

Mirror symmetry applies to all four tools while it's active:

• Build — placing a block places the mirrored version(s) at the corresponding position(s).
• Erase — erasing a block erases the mirrored version(s) too.
• Paint — painting a block repaints the mirrored version(s) in the same material and tint.
• Cursor (Move, Rotate, Copy, Paste) — every Cursor action is mirrored. Moving a block moves the mirrored block to the corresponding destination; rotating one rotates both (with the rotation direction flipped to remain symmetrical).

Mirrored rotations are automatically reversed where needed — so a Roof slope that faces left on your side will face right on the mirrored side, giving you a correctly oriented symmetric roof without having to set each piece manually.

The Mirror Point

The mirror is always centred on the middle of your grid. For a grid 20 blocks wide (X), the mirror axis is at X=10. Whatever you place at X=3 is mirrored to X=17; whatever you place at X=8 is mirrored to X=12.

Blocks placed exactly on the centre line (if your grid has an odd dimension) are not doubled — they're placed once, since they're their own mirror. For even-dimension grids, there's no single centre cell, so every cell placed near the middle is always matched by a mirror copy.

Building Symmetrically

The most effective workflow for symmetric builds:

1. Set your grid to even dimensions if possible — this avoids ambiguity at the centre line.
2. Enable Mirror X, Mirror Z, or both before you start the symmetric section.
3. Build only one "quadrant" (or half) of your intended structure. The mirrors fill in the rest automatically.
4. Once the symmetric section is done, turn mirrors off before adding asymmetric detail — things like a door that only appears on one side, or furniture that shouldn't be doubled.

Practical Examples

Symmetric building facade: Enable Mirror X. Build the left half of your facade — windows, walls, and decorative elements. The right half appears automatically. When you get to the entrance in the centre, turn Mirror X off and place the door once.

Circular garden bed: Enable both Mirror X and Mirror Z. Place one quarter of your garden layout — paths, flower beds, trees. All four quadrants are filled in simultaneously, giving you a rotationally symmetric garden with a quarter of the effort.

Symmetric roof: Enable Mirror X. Place Sloped roof panels down one side of the roofline. Mirror X fills in the opposite slope automatically, with rotations flipped so both sides slope inward correctly.