Asset Generator

Generate PNG images (Gemini or xAI Grok) and GLB 3D models (Tripo3D) from text prompts. These are paid APIs — every call costs real money. Tools live at ${ASSET_GEN_SKILL_DIR}/tools/; run from the project root and keep runtime-loaded outputs under ${RUNTIME_ASSET_DIR}/.

Models

Grok produces great-looking output but often ignores specific instructions; reach for Gemini when the result must match what you described.

Images

python3 ${ASSET_GEN_SKILL_DIR}/tools/asset_gen.py image \
  --prompt "the full prompt" -o ${RUNTIME_ASSET_DIR}/img/car.png

--model (default grok) · --size (default 1K; Gemini also 512/4K) · --aspect-ratio (default 1:1; also 16:9, 9:16, 4:3, 3:4, 3:2, 2:3).

Image-to-image: pass --image ref.png and the model sees the reference — prompt only for what changes (angle, pose, recolor), don't re-describe appearance. Use this for style families (one hero asset → the rest), variants, and multi-view sets.

Small sprites: minimum generation is 1K, so a 1024px image downscaled to 64px looks muddy. Design display sizes ≥128px, or generate a kit (multiple objects in one 1K image) and slice it with tools/grid_slice.py ... --grid 2x2 --names "a,b,c,d", or prompt for bold flat forms that survive downscaling.

Review every PNG before any GLB conversion — a bad image wastes 30¢+ downstream.

Background removal

Read ${ASSET_GEN_SKILL_DIR}/rembg.md. Key rule: never prompt for a "transparent background" (the generator bakes a checkerboard) — prompt a solid color, then matte it out.

Animated sprites

Recipe: reference → pose → video → extract frames → loop-trim → rembg.

1. Reference (Gemini 1K, neutral pose, solid BG) — anchors everything; review carefully.
2. Pose per action: image-to-image from the reference, prompt only the action.
3. Video from the pose frame: asset_gen.py video --image pose.png --duration 2 -o walk.mp4 (--duration 1–15s, --resolution 720p; cost 5¢/s).
4. Extract: ffmpeg -i walk.mp4 -vsync 0 frames/%04d.png.
5. Loop-trim looping cycles (walk/idle): tools/find_loop_frame.py frames/ returns the loop frame; delete frames past it. Skip for one-shots (attack/death).
6. Batch matte: tools/rembg_matting.py --batch frames/ -o clean/.

Reuse one reference for all of a character's actions. Chaining (feed action A's last frame as action B's start) keeps positional continuity — keep chains ≤2 deep, they drift.

3D models

python3 ${ASSET_GEN_SKILL_DIR}/tools/asset_gen.py glb  --image ref.png -o model.glb     # 30¢ default / 60¢ --quality hd
python3 ${ASSET_GEN_SKILL_DIR}/tools/asset_gen.py rig  --image ref.png -o rigged.glb    # +25¢, biped only
python3 ${ASSET_GEN_SKILL_DIR}/tools/asset_gen.py retarget --rigged rigged.glb \
  --animation preset:biped:walk -o walk.glb                                             # 10¢ per clip

Source image for glb: 3/4 elevated angle, solid white/gray background, matte finish, opaque glass, single centered subject — and do not rembg it (Tripo3D needs the solid bg). rig is biped-only and aborts if the mesh isn't humanoid; quadrupeds use plain glb. retarget reuses the rigged task id — run it once per animation against the same rigged GLB (no re-rigging). Don't assume the preset name survives into the GLB; inspect the imported clip names before wiring playback.

Biped retarget presets (pass as preset:biped:<name>):

afraid agree angry_01/02/03 basketball_shot bow box_01/02/03 cast_a_spell cheer chop
clap climb complain_01/02 cross_body_crunch crossover_dribble cry dance_01..06
defeat_02/03 depressed dig dive dribble fall fire flee_01/02 flip fold_arms
football_catch/save/pass freaky frightened front_kick_01/02 frustrated_01/02 golf
greet_01..04 heart_pose hit_to_body_01/02 hit_to_head/side/stomach hug hurt idle
jump jump_down jump_rope_01/02 laugh_01/02 lift_heavy look_around make_a_call_01/02
pitch_baseball play_mobile_game play_video_game press-up run run_upstairs scared_01/02
scratch shoot shovel sing_01..04 sit slash sob standing_relax surf swagger swim turn
victory_celebration volleyball wait walk warm_up wave_goodbye_01/02

Tripo3D operations (important — avoids double-charging)

• Jobs routinely sit at 99% with empty output for minutes. Let the default timeout run.
• A timeout in glb/rig/retarget does not mean server failure. The task id is already saved in the <output>.tripo.json sidecar. Do not resubmit — that double-charges. Resume for free instead:

  python3 ${ASSET_GEN_SKILL_DIR}/tools/asset_gen.py resume -o model.glb

  Safe to re-run; it no-ops once complete. Delete the sidecar to force a cold start.

Costs

Each generation costs real money, so confirm with the user before generating. Quick reference: texture/simple sprite (Grok) 2¢ · character/ref (Gemini 1K) 7¢ · background 2¢ (Grok) or 10¢ (Gemini 2K) · full 3D asset 37¢ (7¢ image + 30¢ GLB) · rigged character walk/idle/attack ≈ 92¢.

Output and logging

Each command prints JSON to stdout: {"ok": true, "path": "...", "cost_cents": 7}. Progress goes to stderr — redirect it to a temp file and read only on failure to keep context clean:

_log=$(mktemp)
result=$(python3 ${ASSET_GEN_SKILL_DIR}/tools/asset_gen.py image --prompt "..." -o p.png 2>"$_log") || tail -20 "$_log"

Generate independent images in parallel (multiple Bash calls in one message).

Visual pitfalls

Generators and vision checks have weak spatial sense — verify from screenshots when it matters.

• Direction/orientation is unreliable ("facing left" vs "right" often comes out identical). Generate one direction and flip horizontally at runtime rather than paying for the mirror.
• Mixed sizes: image frames are ~1024px, video frames ~720px. Downscale everything to the smallest source before matting (magick in.png -resize 720x720 out.png).
• Playback fps: source videos are ~24fps — drive sprite playback off elapsed time at ~1/24s, and only restart a loop when the animation state actually changes.

Asset manifest (in README.md)

Track every generated asset in README.md with an in-game Size column — without it, coders consistently scale assets wrong:

• 3D models: meters, e.g. 4m long, 1.8m tall, 0.3m
• Textures: tile size, e.g. 2m tile
• Backgrounds: pixel size + behavior, e.g. 1920x1080, fullscreen
• Sprites: display pixels, e.g. 128x128 px