Mirror

A mirror folds a projector’s beam — useful for short-throw rigs, snorkel-style installations, and any case where the physical projector body can’t sit on the optical axis. The mirror is a property of the projector, not a separate scene object: Mapping Matter models the reflection geometry, shows the folded beam path, and warns when the projector overshoots the mirror.

Enable the mirror

Select the projector you want to fold.
In the projector’s Properties panel, expand the Mirror collapsible.
Toggle Mirror on. A mirror plate appears attached to the projector, sized to the beam by default.
Drag the mirror plate in the viewport to position it between the projector and the surface; drag the projector’s target point to aim the folded beam.

Suggested mirror for UST lenses

If the active lens has a large fixed optical offset — typical of ultra-short-throw lenses, where the image projects steeply off-axis — the projector sidebar shows a UST lens — add a fold mirror? hint banner with an Add suggested mirror button. Click it and Mapping Matter picks a fold-mirror placement (offset, 45° starter pitch, plate size) that bends the chief ray onto the projector’s current target. From there you can fine-tune position, rotation and dimensions like any other mirror. The banner only appears while no mirror is enabled; once you add one, manually or via the button, it goes away.

When the mirror is selected, the gizmo target rotates the mirror itself rather than the projector — this lets you tilt the mirror without changing the projector’s pose.

Beam footprint on the plate

While the mirror is enabled, Mapping Matter draws the projector’s beam footprint as an amber quad on the plate itself — exactly where the rays land (visible on the plate in the clip above). This makes it easy to size and position the plate against the optical surface without leaving the viewport. The amber tint stays visible even when the plate flips red for overshoot, so you can read both signals at once.

The mirror sidebar’s Scale mirror to fit button resizes the plate to the smallest dimensions that contain every frustum corner — useful when the default plate size is too generous or has been shrunk past the beam. Dimensions round up to the next 10 mm so a numerical residual doesn’t leave the overshoot tint flickering on the edge.

Beam overshoot warning

If the projector beam falls outside the mirror plate boundary, Mapping Matter tints the overshooting beam red and the mirror plate edges that are clipped. Resize the mirror in its Properties (or use Scale mirror to fit) or reposition the projector to clear the warning.

Mirror properties

In the projector’s Properties panel, under the Mirror section:

Product — pick a manufacturer mirror from the catalogue (loads body mesh and dimensions), or use a generic flat plate.
Width / Height — physical dimensions of the mirror plate.
Offset — X / Y / Z offset from the projector body.
Rotation — pitch / yaw / roll relative to the projector.

Changes update the folded beam path in real time.

Limitations

Mapping Matter simulates a single, perfectly flat, 100% reflective mirror. Brightness loss from real mirrors should be accounted for separately when reading the photometric outputs.
Mirror assemblies in the catalogue are reference geometry — confirm dimensions and mounting with the manufacturer before relying on them on-site.