OC Theme Block

Every character stands somewhere, and the "somewhere" does half the mood work. OC Theme Block is the ComfyUI-OC-Generator node that answers the where: 304 environment, atmosphere, background, and lighting options - the biggest catalog in the pack. Airport, alley, aquarium, autumn, backlit at dusk, an Alps backdrop - pick one and the correct tag appears in your prompt without a single misspelling.

It's the pack's theme slot, covering ten subgroups: 季节 (seasons), 天气 (weather), 自然景观 (natural scenery), 氛围 (atmosphere), 室外 (outdoors), 城市 (city), 室内 (indoors), 浴室 (bathroom), 背景 (background), and 光照 (lighting). That's a wide net - it's the node you reach for when the setting matters as much as the character, and it's deliberately the first block in the pack's prompt order. Theme goes at the front of the assembled prompt, before species, body, and outfit, because the model builds the scene around it.

Controls, in the pack's standard shape

If you've touched any OC block, this is familiar territory:

• mode - fixed keeps your pick; randomize samples within the current group; increment/decrement step through the pool using the optional step size. The stepping modes are great here - you can sweep a character through ten backgrounds in ten runs.
• option - the static dropdown over the full 304-option catalog.
• group - narrows the active pool to one subgroup (say, 光照 if you only want lighting conditions).

Optional enabled (mute without deleting) and seed (reproducible randomize). Outputs are oc_block, prompt_preview, and debug_text; wire oc_block into OC Generator and it slots the theme tag first, with against backlight at dusk reading just as it should.

The familiar trap, plus one nuance

The static-dropdown/group mismatch applies here too - select an option outside your group and the node silently falls back to the first valid item in that group, flagged only in debug_text (requested option not in current group; fallback applied.). With ten groups and 304 options, that's the highest-probability confusion in the whole pack. The nuance for theme specifically: many groups overlap semantically (a city street could sit under 城市 or 室外), so a fallback is more likely to land somewhere visually adjacent - which makes it easier to miss.

Install

Same light story as every node in this pack: no models, no pip dependencies, JSON tag data shipped in-repo.

cd ComfyUI/custom_nodes
git clone https://github.com/Zhuozhuo-219/ComfyUI-OC-Generator

Or search "ComfyUI-OC-Generator" in ComfyUI Manager, install, restart. It shows up under OC Generator → Blocks. One standing reminder: this builds prompt text, so point the result at an anime SDXL checkpoint (Illustrious, NoobAI, Pony) where these scene tags are part of the model's vocabulary.