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Render Asset Thumbnail

Renders a 500x500 PNG preview for the currently selected asset datablock (Collection, Object, Material, or Geometry Nodes) and assigns it as that datablock's custom asset preview. The operator drives Blender's viewport OpenGL render with an auto-framed camera and, when the selection covers multiple asset-marked collections, renders each one in turn with isolation so they do not overlap.

bl_idname: iops.assets_render_asset_thumbnail Mode: Object Context: VIEW_3D Modal: no HUD: no

Overview

Blender's built-in "Generate Preview" for asset datablocks uses a fixed camera angle and tight framing that often clips or under-fills the thumbnail, and it does not handle collection-instance empties well. This operator replaces that workflow with a configurable pass: pick a view direction (current 3D viewport, 3/4 right/left, front, side), a focal length, a framing margin preset, and let it render. Collection-instance empties are framed against the geometry they spawn via the dependency graph, not their tiny display gizmos.

When a selection spans several asset-marked collections, the operator enters a batch mode that isolates each collection (local view, falling back to per-object hide_viewport), renders, assigns the preview, and restores state — one thumbnail per asset in a single invocation. A header-text progress indicator runs on every 3D viewport during the batch.

The render output is a temporary PNG in the system temp dir under iops_thumb/; the file is unlinked after the preview is loaded onto the datablock.

Usage

  • Selection: at least one asset datablock reachable from the active selection. For COLLECTION mode this is asset-marked collections found from the selection (batch path) or context.collection. For OBJECT / MATERIAL / GEOMETRY modes the active object is used (MATERIAL / GEOMETRY additionally require a MESH).
  • Context: must run from a VIEW_3D — the operator needs a 3D viewport for both framing and render.opengl.
  • Invocation: no default keymap binding. Run via F3 search ("Render Active Asset Thumbnail"), the Assets pie (iops.call_pie_assets), or any custom binding you add.

Steps:

  1. Select the asset(s) in the 3D viewport or outliner.
  2. Run the operator.
  3. Adjust Render For, Camera View, Lens, Distance, framing style, and alpha in the F6 redo panel — undo and re-execute as needed.

Properties

Name Type Default Description
render_for Enum COLLECTION Target type. Items: OBJECT (Object), COLLECTION (Collection), MATERIAL (Material), GEOMETRY (Geometry Nodes).
camera_view Enum CURRENT View direction. Items: CURRENT (Current View — read from active 3D viewport region_3d), THREE_QUARTER_RIGHT (3/4 Right), THREE_QUARTER_LEFT (3/4 Left), FRONT, SIDE.
thumbnail_lens Float 90.0 Focal length in mm. Min 1.0, max 200.0. Used directly for the temp camera and as the viewport space.lens during viewport render.
persp_distance Float (FACTOR) 1.0 Camera distance multiplier on top of the auto-fit distance. Min 0.1, max 5.0, soft range 0.5–2.0.
use_framing Bool True Auto-frame the asset to fill the thumbnail. When off, the current viewport view is used as-is.
framing_style Enum TIGHT Padding preset: TIGHT (5%, multiplier 1.05), BALANCED (16%, 1.16 — matches Blender asset style), LOOSE (30%, 1.30), CUSTOM (use frame_margin).
frame_margin Float (FACTOR) 0.16 Custom margin multiplier added to 1.0. Min 0.0, max 0.5, soft range 0.05–0.35. Only used when framing_style = CUSTOM.
use_alpha Bool True Render with transparent background (RGBA + film_transparent). When off: RGB with solid background.
toggle_overlays Bool True Hide viewport overlays during the render and restore afterward.

Notes

  • Render is fixed to 500x500 PNG. Resolution / file format / color mode / film_transparent are saved before and restored after the render — your scene render settings are not modified persistently.
  • Saved-and-restored viewport state per render: view_perspective, view_distance, view_location, view_rotation, space.lens, overlays, and shading.show_background.
  • The viewport OpenGL path is tried first; if no 3D viewport region_3d is available the operator falls back to a temporary camera (IOPS_Thumbnail_Cam) plus render.opengl(write_still=False) with a temp_override onto the first VIEW_3D area.
  • Save path tries three strategies in order: Image.save_render, Image.save after setting filepath, and finally a pixel-copy into a fresh bpy.data.images.new image that gets .save()'d. Output is unlinked from disk after ed.lib_id_load_custom_preview loads it onto the datablock.
  • Batch COLLECTION mode (triggered when find_asset_collections_from_selection returns one or more asset-marked collections) isolates each collection via view3d.localview. If local view cannot be entered, per-object hide_viewport is used with a keep-alive set that includes the target collection plus, recursively, every collection referenced via a collection-instance empty inside it. LayerCollection.exclude / hide_viewport and eye-icon hide_set state are never touched.
  • Linked datablocks (datablock.library is not None) are skipped silently in the non-batch path; the operator reports a warning if no local asset datablocks remain.
  • Collection-instance empties are framed against depsgraph-spawned geometry via compute_combined_bound_box walking depsgraph.object_instances, falling back to raw bound boxes only when no framable geometry is found.
  • Header text on all 3D viewports shows IOPS Thumbnail i/N: rendering '<name>'... during batch progress, plus a cursor progress bar through wm.progress_begin/update/end. Per-asset success/failure is also printed to the console with the [IOPS Thumbnail] prefix.
  • bl_options = {"REGISTER", "UNDO"} — supports F6 redo, but the preview assignment side-effect is not undoable in the usual sense; rerunning the operator overwrites the preview.