User Guide¶

Numbered callout markers and leader lines for technical Blender scenes. This guide covers installation, day-to-day usage, known limits, and troubleshooting.

What's in the package¶

explocallout-1.0.0.zip — the ExploCallout add-on: a small Blender extension that automates numbering, layout, and camera framing from a side panel. Optional, but it's the recommended workflow to use the asset (see "How it works" below). Source included, GPL-licensed — see License.
explocallout.blend — the asset file. It contains one asset: the TO_Callouts Geometry Nodes node group (marked in the Asset Browser under RevealForge › Callouts), plus a small example assembly scene with callouts already applied so you can see the result before touching anything.
blender_assets.cats.txt — the asset catalog definition. Keep it in the same folder as the .blend file so Blender's Asset Browser can read it.
This guide, the license, and the license files.

See Compatibility for the supported Blender versions and how that's been verified.

Installation¶

The add-on is optional, but it's the recommended workflow to get consistent numbering, layout, and camera framing — Option A below. If you'd rather work with the node group directly, Options B and C skip the add-on entirely. They aren't mutually exclusive: you can install the add-on and still append/link the node group into other files.

Option A — Install the add-on (recommended)¶

In Blender, open Edit > Preferences > Get Extensions, click the dropdown next to the search field, and choose Install from Disk.
Select explocallout-1.0.0.zip from the package and confirm. Blender installs and enables the add-on — nothing else to toggle on.
In any 3D Viewport, press N to open the side panel and look for the ExploCallout tab. That's the panel described in "How it works" below.
The add-on needs explocallout.blend (from this same package) to find the TO_Callouts node group. If it's already loaded in your current file (you appended or linked it before), that's used directly. Otherwise it looks for explocallout.blend automatically, in order: the Library field in the panel (if you set one), the add-on's own install folder, the root folder of any Blender asset library you've registered (Option B below — the .blend must sit directly in that folder, not in a subfolder), and finally the folder of the .blend file you currently have open. The simplest setup: put explocallout.blend and blender_assets.cats.txt directly in an asset library's root folder (Option B, step 1-2) and the add-on finds them without any extra configuration. Otherwise, point the panel's Library field at wherever you put explocallout.blend.

Option B — Add as an Asset Library (node group only)¶

Put the .blend file (and blender_assets.cats.txt) in a folder you control, e.g. Documents/BlenderAssets/ExploCallout/.
In Blender, open Edit > Preferences > File Paths > Asset Libraries and click + to add a new library pointing at that folder.
Open the Asset Browser in any 3D Viewport (the icon in the top-left of the editor type dropdown), pick your new library, and you'll see the TO_Callouts node group under RevealForge › Callouts (that's the asset's technical/internal name — it's what the Asset Browser tile shows, distinct from the "ExploCallout" product name on this guide's cover).
Drag the node group onto any mesh object in your scene, or use the Add > Node Group menu inside a Geometry Nodes modifier.

Option C — Append or Link directly (node group only)¶

In the file you're working on, go to File > Append (or Link if you want to keep the asset updated from the source file), navigate into explocallout.blend > NodeTree, and select TO_Callouts.
The node group is now available in your file's Geometry Nodes modifier node group picker.

Append copies the node group into your file (safe, self-contained). Link keeps a live reference to the original .blend file (useful if you want updates to the node group to propagate automatically, but the original file must stay reachable at its path).

How it works¶

With the add-on installed (Option A), the fast path is:

Open the ExploCallout tab in the 3D Viewport's side panel (N).
In the Targets section, leave Scope on its default, Scene, to label every eligible mesh in the scene — or set it to Selected and select just the parts you want to label. Start Index sets the first number used; parts are always numbered in name order, character by character (shown as Order: Name (A-Z), not editable in this version) — so Part10 sorts before Part2. Use zero-padded names (Part01, Part02, ...) to get the numbering you expect.
Click Apply Callouts. In one step, it numbers your parts, builds the anchor points, applies TO_Callouts, adds the numbered labels, and (if Create Preview Camera is checked, on by default in the Camera section) frames a preview camera. Clear Callouts removes everything the add-on generated, if you want to start over.
Adjust Label Distance, Label Spread, Tiers, Marker Radius, Leader Radius, and Text Height in the panel, then click Apply Callouts again to rebuild with the new values.
Drag a label to a better spot in the viewport, then click Sync Leaders — the leader line follows it to the new position.
Click Frame Camera whenever you change the camera preset or aspect ratio, to reframe on the current layout.
Press F12 to render. The add-on never writes a render file on its own — it only sets up the scene for your usual render step.

Use Check Layout after an Apply or Frame Camera (it needs an active camera to measure against, and reports an error if there isn't one) to look for overlapping labels or anything outside a 5% safe-area margin — it reports the number of overlapping label pairs, shows the safe-area status in the panel, and selects the labels at fault (a piece outside the safe area only shows up in the warning message, not in the selection).

TO_Callouts itself does the actual geometry work: it takes a cloud of anchor points (one per part you want to label) and, for each anchor, generates a small marker (an icosphere) and a leader line running out to a label position. The add-on builds that point cloud, applies the node group, and creates the numbered text objects (with a camera-facing constraint) for you — see "Without the add-on" below if you'd rather build all of that by hand.

The bundled example scene shows the result end-to-end for a 6-piece mounting bracket assembly — open it, select the objects, and inspect the modifier stack and the anchor points object to see a working reference.

Without the add-on¶

If you installed the node group without the add-on (Option B or C), the same result is possible, but every step below is manual. TO_Callouts expects a label_offset vector attribute on the anchor points — a vector from the anchor to where you want the label to sit.

There are two starting points — pick one, the steps that follow differ:

Starting from the example scene's points object (duplicate):

Duplicate the example scene's anchor point object (Object > Duplicate). It already carries the label_offset attribute and the TO_Callouts Geometry Nodes modifier — you don't add either again (see "Starting from scratch" below for why re-adding the attribute is a mistake on a duplicate). Edit its vertices and label_offset values for your own parts, keeping the transform rule in step 2.
Keep this points object's own transform at the default — Location (0, 0, 0), Rotation 0, Scale 1 (Object > Apply > All Transforms if you moved it). Mesh vertex coordinates are always in the object's local space; with an identity transform, local space and world space line up, so a vertex placed at a part's world position (snap to origin, Shift+S > Selection to Cursor with the 3D cursor at the part's origin) is stored correctly. If you ever give this object its own location/rotation, you'll need to place vertices in its local space instead, not world space — easiest to just leave the transform at default and avoid the conversion entirely.

Starting from scratch (a plain mesh, single vertex per part):

Create a new mesh object with one vertex per part, placed at each part's world position (same transform rule as step 2 above).
Add a label_offset attribute and set each point's value with a short script, from the Scripting workspace's Python console (with the points object selected): python import bpy obj = bpy.context.object attr = obj.data.attributes.get("label_offset") if attr is None: attr = obj.data.attributes.new(name="label_offset", type="FLOAT_VECTOR", domain="POINT") attr.data[0].vector = (0.3, 0.0, 0.2) # repeat per point index, one call per vertex Each vector points away from the part center toward where you want its number to sit; attr.data[i] follows the same vertex order as the points object's vertices. Use attributes.get(...) first, not attributes.new(...) directly — on a fresh object it's a no-op (the attribute doesn't exist yet), but calling new on an object that already has a label_offset attribute (e.g. a duplicate of the example points object) creates a second, differently-named attribute that TO_Callouts never reads.
Add the TO_Callouts node group as a Geometry Nodes modifier on that points object, and adjust Marker Radius / Leader Radius to match your scene scale.

Either way, finish with:

Add a numbered text object (Text object, Add > Text) at each label position, with a Track To constraint pointing at your camera, so labels always face it.

Presets and framing¶

With the add-on, the panel's Camera section is a built-in preset picker: choose Hero (3/4), Overhead (3/4), or Flank (3/4), pick an Aspect (16:9, 9:16, or Scene to match your current render resolution), and click Frame Camera to (re)position the preview camera for that combination. Run it again any time you change a setting or move labels, to reframe on the current layout.

Aspect and your render resolution. Whenever the add-on frames the preview camera — clicking Frame Camera, or Apply Callouts with Create Preview Camera on (the default) — choosing 16:9 or 9:16 also sets your scene's render resolution to a fixed 1280x720 or 720x1280 and makes the preview camera the active camera. If you're rendering at a specific resolution (e.g. 4K) and don't want it overwritten, choose Scene instead, which reads and keeps your current render resolution. Turning off Create Preview Camera skips this entirely on Apply (no camera framed, no resolution change); any preview camera from an earlier Apply is removed too, so set your own scene camera as active before rendering.

The example scene demonstrates the Hero (3/4) angle. All three presets avoid a flat profile view, which tends to compress leader lines and cause label overlap:

Hero (3/4) — classic three-quarter product angle, moderate elevation.
Overhead (3/4) — steep top-down angle, good for flat/plan-style parts.
Flank (3/4) — three-quarter from the opposite side, same elevation as hero (useful when the hero angle occludes a part you need visible).

Without the add-on, camera framing is a manual step, same as any other camera placement in Blender — the three angles above are still a good starting point. For output framing, both 16:9 (landscape, e.g. video/slides) and 9:16 (portrait, e.g. social/vertical video) work well with this node group — keep at least a 5% margin from the frame edges for both geometry and labels so nothing gets clipped at render time (the add-on's Check Layout button checks this margin for you).

Known limits¶

Readability depends on your own label layout — there's a practical ceiling. The node group's marker/leader geometry scales with anchor count — we verified clean results up to 50 anchors during development and haven't pushed past that. But since you choose where each label sits (the label_offset per anchor, cf. "How it works" above), the real-world ceiling is about how tightly your own layout packs leader lines, not something the node group manages for you. As a rule of thumb, once more than about 20 leader lines converge on a small assembly, visually tracing "which line goes to which part" gets hard for a human viewer even if nothing technically overlaps. For larger assemblies, consider labeling in groups/zones rather than one single dense cluster.
No flat "profile" camera preset. A near-0-degree elevation angle flattens the ring layout into a near-straight line and risks label collisions — stick to a 3/4-style angle (see above).
Apply Callouts rebuilds everything from scratch, every time. Clicking Apply Callouts deletes and regenerates every marker, leader line, and label — including any you dragged into a custom position with Sync Leaders. There's no way to change one setting and keep your manual moves; the next Apply always starts over. Do your slider adjustments first, drag labels into their final spots last, and only click Apply Callouts again after that if you change a setting — otherwise you'll lose the manual moves.
Realize (bake) and manual label moves don't combine in this version. If Realize (bake) geometry is on, the leader-line geometry is converted to a fixed mesh at the next Apply Callouts, and Sync Leaders becomes unavailable (greyed out) afterwards — there's nothing live left to update. Turning Realize on always requires one more click on Apply Callouts to actually perform the bake, and that Apply wipes any manual label moves you made first (previous point) — there's no way around this in this version. So: if you want the baked, static geometry, accept the computed (non-dragged) label positions and turn Realize on before your last Apply. If you want your own manual label positions, leave Realize off — Sync Leaders will keep working, but the leader-line geometry stays live (not baked).
The numbered text is regular Blender text objects, not procedural Geometry Nodes text. This is intentional — it keeps text billboarding and inspection simple and reliable. With the add-on, clicking Apply Callouts regenerates and renumbers the whole set automatically. What's still a manual step (or your own script) is adding or duplicating a single extra label without a full re-apply — e.g. splitting one part into two callouts by hand.
File formats. The package ships as a native .blend asset. To export to .glb/.gltf/.fbx, duplicate the object first, then Convert to Mesh on the duplicate before exporting (exporters don't always preserve live Geometry Nodes modifiers, and Convert to Mesh replaces the live modifier with a static mesh on whichever object you run it on) — not a distributed conversion step in this version.

Troubleshooting¶

I found a part that doesn't get a callout / labels overlap in my scene. With the add-on: the anchor is the part's own object origin, not a vertex — double-check (a) the part is a mesh object with its origin placed where you want the callout to point (Object > Set Origin if it's off), and (b) if Scope is set to Selected, that the part is actually selected. Without the add-on (manual flow, see Without the add-on above): double-check (a) the anchor points object has a real vertex at the part's intended anchor world position, and (b) your label_offset vector isn't pointing toward another part's label position. The example scene is the reference for a known-good setup.

For anything not covered here, see FAQ or Contact / Help.