Baking hangs on Applying Materials

[esonx3]

Describe the Bug
crash report

To Reproduce
Steps to reproduce the behavior:

1. select your object before making any generations and click "Bake textures"
2. blender hangs on "Applying Materials to Object".

NOTE! This also happens (randomly?) after a generation have completed successfully

Expected Behavior
new material is applied to the selected object

Actual Behavior
blender hangs on Applying Materials

System Information:

• Blender Version: 4.5
• StableGen Version: 0.1.0
• Operating System: win 10
• ComfyUI Installation: e.g., Standard local install
• GPU: NVIDIA RTX 3080

[sakalond]

Yeah, I also get this sometimes with baking. I will have to look into it. So far I wasn't able to find the cause.

[coolguy42]

For me this issue still happens but only when I have the "material properties" tab open. With any other tab open it works totally fine. Of course that's the most common tab to have open when diagnosing baking issues.. Blender 4.5.4

[sakalond]

It's possible there is some bug. But I mostly rewrote the baking as I will be adding PBR texturing soon, so it's possible I also fixed this bug by doing that.

Probably wait for the release and then test again, if it's still there I will take a closer look.

[xjxxjx1017]

According to Claude Code:
In blender 4.5, setting engine to the current engine in use will cause it to hang.

Here is the .md file that I recorded during the fix in my local code. I guess the actual fix is in Layer 2, the other one might be irelavent.

===============

Bug: Blender Freezes Permanently at "Applying Material to …" During Bake Textures

Date: 2026-04-14
Blender: 4.5.5
File: render_tools.py

---

Symptom

Running Bake Textures in StableGen caused Blender to freeze permanently. The status bar showed "Applying Material to {object name}" and Blender never recovered — required force-quit.

---

Root Cause

The freeze had two layers:

Layer 1 — Infinite retry loop (silent exception)

The modal operator's apply_material phase called add_baked_material() with no try/except. If that function raised any exception, _current_index was never incremented, so every subsequent 0.1 s timer tick retried the same failing object — creating an infinite silent loop that appeared as a freeze.

Two bugs inside add_baked_material could trigger this:

• obj.data.uv_layers[0].name — IndexError if the object had no UV layers
• for node in nodes: nodes.remove(node) — mutating a live Blender collection during iteration (undefined behavior)

Layer 2 — Cycles engine reload on no-op assignment (confirmed root cause)

After baking completes, the cleanup code unconditionally restored the render engine:

bpy.context.scene.render.engine = self.original_engine  # e.g. 'CYCLES'

When the scene was already using Cycles before baking started, this assigned 'CYCLES' to a property that was already 'CYCLES'. In Blender 4.5, writing to render.engine always fires an engine reload callback — even when the value is unchanged. This Cycles reinitialisation hung the main thread permanently.

The same no-op assignment also existed in execute() when switching to Cycles for baking.

---

Diagnosis Method

Added numbered print() checkpoints throughout add_baked_material() and the cleanup code, then watched Blender's System Console (Window → Toggle System Console) in real time. The last line printed before the freeze was:

[StableGen DEBUG] CLEANUP - restoring render engine to 'CYCLES'

This pinpointed the exact hanging line.

---

Fixes Applied

Location	Change
modal() ~line 5360	Wrapped add_baked_material() call in try/except so _current_index always increments, breaking any infinite retry loop
add_baked_material() node clear	for node in nodes: nodes.remove(node) → nodes.clear()
add_baked_material() UV access	Added guard: obj.data.uv_layers[0].name if obj.data.uv_layers else ""
add_baked_material() image loads	Added check_existing=True to all 7 bpy.data.images.load() calls to avoid redundant disk I/O
add_baked_material() polygon loop	for poly in obj.data.polygons: poly.material_index = mat_index → foreach_set() bulk assignment
modal() cleanup	bpy.context.scene.render.engine = self.original_engine → guarded with if bpy.context.scene.render.engine != self.original_engine (primary freeze fix)
execute()	bpy.context.scene.render.engine = 'CYCLES' → guarded with if bpy.context.scene.render.engine != 'CYCLES'

[sakalond]

Thanks, I will look into it. Sounds reasonable, and easy to fix.