vse-linear-modifiers

VSE linear modifiers attribute

Pathology witness for the 5.2 removal of Strip.use_linear_modifiers. A COLOR strip is enough; there is no geometry and no gallery still (same class as exit-pre-sidecar, ngon-triangulate).

Follows vse-python and the version-gated assertion shape of gn-modifier-inputs (per-version contract, exit 0 on every matrix leg). Scaffolding matches cross-version-property-delete (check() returns, argparse naive-API flag, FATAL wrapper). That example does not version-branch — del is the same on 4.5 and 5.x — so the gate itself is copied from gn-modifier-inputs, not from del.

What it witnesses: use_linear_modifiers is a bool you can set on a strip on 4.5.11 and 5.1.2. The same getattr/setattr is AttributeError on 5.2.1. hasattr then read never raises on any of the three.

The identifier is Strip, not Sequence. Earlier text here named Sequence.use_linear_modifiers. bpy.types.Sequence does not exist on 4.5.11, 5.1.2 or 5.2.1. The strip types are Strip / ColorStrip, and the attribute is defined on the Strip base (the class chain is ColorStrip → EffectStrip → Strip), so every strip type had it. Anyone searching the API docs for Sequence will not find it.

What failure each check would catch:

• exit 3 — COLOR strip never landed
• exit 4 — attribute missing where the naive/legacy path requires it (--assume-present on 5.2 lands here)
• exit 5 — attribute still present, or getattr silent, on 5.2+
• exit 6 — setattr did not round-trip on 4.5 / 5.1
• exit 7 — the hasattr guard still raised

--assume-present is the falsifier: skip the version gate and demand the 4.5 RNA. It exits 0 on 4.5.11 and 5.1.2 (the old API still works) and 4 on 5.2.1. That is unlike --same-axis, which is red on every binary.

No SMOKE_SKIP. Every matrix leg exercises the contract.

Who hits this

Add-ons, presets and conform scripts that set strip.use_linear_modifiers = True so colour-balance and curve modifiers work in linear space. On 5.2 that line raises AttributeError: 'ColorStrip' object has no attribute 'use_linear_modifiers' (or the matching strip type), and the script stops at the first strip. The RNA description on 4.5 and 5.1 reads:

Calculate modifiers in linear space instead of sequencer's space

The default is False on both. On 5.2.1 there is no replacement property: no identifier containing linear exists on Strip or on the strip modifier (COLOR_BALANCE listed as a representative). Guard the write with hasattr, as guarded_read does for the read. This example does not claim how 5.2 chooses the colour space for strip modifiers; it measures only that the switch is gone from RNA.

Re-verified

Measurement	4.5.11	5.1.2	5.2.1
bpy.types.Sequence exists	no	no	no
Attribute defined on	Strip	Strip	— (removed)
Default	False	False	—
linear-named property on Strip / strip modifier	yes / no	yes / —	no / no
default exit	0	0	0
--assume-present exit	0	0	4

Exiting 0 on 4.5.11 and 5.1.2 under the falsifier is correct by design. The attribute exists there, so the naive read works; the falsifier exists to fail where it was removed.

Observed while re-verifying, outside this contract: on 5.1.2 in background mode, strip.modifiers.new(name=..., type="COLOR_BALANCE") on a COLOR strip created in factory-empty crashes Blender with EXCEPTION_ACCESS_VIOLATION. The same call works on 4.5.11 and 5.2.1. This example never adds a modifier, so its checks are unaffected.

API reference

• bpy.types.Strip (4.5 LTS, where use_linear_modifiers is documented)
• bpy.types.StripModifier

Run

blender --background --python vse_linear_modifiers.py --
blender --background --python vse_linear_modifiers.py -- --assume-present

Exit codes

Per-script sequential checks. 9 is a valid check code; there is no rule against it.

Code	Meaning
0	Success
1	Uncaught exception (FATAL wrapper)
2	argparse / usage
3	COLOR strip was not created
4	use_linear_modifiers missing when required (--assume-present on 5.2)
5	Attribute still present or getattr silent on 5.2+
6	setattr round-trip failed
7	hasattr-guarded read raised

The blender-smoke workflow runs the check on Blender 5.2 LTS and 4.5 LTS (5.1 on the weekly cron, the needs-5.1 PR label, or manual dispatch). Smoke does not pass --assume-present.