Blender Camera Framing

Blender camera framing

Use scripts/camera_framing.py when a named subject must be wholly visible in the scene camera. The helper uses evaluated world bounds, the active render dimensions and pixel aspect, and Blender's own camera frame. It does not guess from an object's dimensions or from one generic field-of-view angle.

Read references/framing-contract.md before changing the helper or composing a custom framing transaction.

Choose the correct kind of framing

• Render-camera framing changes a Camera object and works in interactive or background Blender. Use this skill for a render, export, shot, or reproducible camera result.
• Viewport framing changes RegionView3D in one visible VIEW_3D area. bpy.ops.view3d.view_selected requires an area/region override, does not work in background mode, and does not fit the scene camera. Use it only to prepare an interactive screenshot and restore selection afterward.

Never report viewport framing as proof that the render camera sees the subject.

Inspect before fitting

1. Name the Camera object and every subject root explicitly. Decide whether descendants and evaluated instances belong to the subject.
2. Inspect the current frame, render resolution percentage, pixel aspect, camera type, lens or orthographic scale, sensor fit, shift, constraints, and clipping.
3. Choose a per-edge image margin. 0.08 means every evaluated bound point must land inside UV [0.08, 0.92] on both axes.
4. Preserve the current viewing direction unless the user supplied a view. view_from is the world direction from target toward camera, not camera toward target.
5. Use the evaluated bounds center as target by default. An optional existing Empty can provide a deliberate off-center look target. Creating or moving an Empty is an explicit behavior, never an implicit side effect.

Execute through Blender MCP

Use the provider's Python-execution tool. Prepend MCP_CONFIG, then append the complete helper source in the same call:

MCP_CONFIG = {
    "camera_name": "CAM-product",
    "object_names": ["GEO-product"],
    "margin": 0.08,
    "include_descendants": True,
    "include_instances": True,
    "set_scene_camera": True,
}
# Append the complete contents of scripts/camera_framing.py here.

The helper detects MCP_CONFIG, performs one bounded transaction, and prints one blender.camera-frame/v1 JSON object. Do not send only the path: the Blender MCP process may not share the agent's filesystem. Do not add sleeps, viewport operators, a render, or a save to this transaction.

For caller-owned offline work, run Blender directly:

blender --background scene.blend --python scripts/camera_framing.py -- \
  --camera CAM-product --objects GEO-product GEO-label --margin 0.08 \
  --include-descendants --include-instances --set-scene-camera

Add --save-as /absolute/caller-owned/output.blend only when the user requested that derivative. The helper never overwrites the input file implicitly.

Validate the result

Require all of the following in the returned JSON:

• ok and verification.fits are true;
• no requested name is missing and at least one evaluated bound was used;
• verification.outside_count and behind_count are zero;
• projected U/V extrema remain inside the declared safe UV rectangle;
• fitted near/far clips enclose the reported camera-depth range;
• the camera type, effective render dimensions, pixel aspect, target, and evaluated object/instance counts match the request.

Then render one inexpensive representative image and inspect it. Bounds fitting proves geometric inclusion, not a pleasing composition, unobstructed subject, correct depth of field, or adequate negative space. Refine view direction, target, lens, and margin deliberately; rerun the helper after each optics or resolution change.

As an independent final check, run blender-python-execution's scripts/scene_audit.py against the same roots, margin, descendant policy, and instance policy. Deliberately distinct fitting and audit implementations reduce the chance that one algebra or selection bug certifies itself.

Failure rules

• Missing objects, an empty-only subject, non-finite bounds, a zero view vector, a missing requested target Empty, unsupported camera projection, or explicit clips that exclude the subject are hard failures.
• Transform-affecting camera constraints are rejected by default. Remove or deliberately manage them in a separate transaction; do not fight their evaluated result silently.
• If camera shift plus margin places the optical axis outside the safe frame, choose a smaller shift/margin or a different explicit composition.
• If Geometry Nodes or collection instances are important, inspect the reported instance count and render a control. Instance discovery is dependency-graph best effort and is reported separately from direct evaluated objects.
• Refit at each required animation sample when the subject, target, camera parent, modifier output, or render settings animate.