godot-validation

Godot Visual Validation

Validate lesson shaders by applying them to PBR-textured meshes in test-scene/ and capturing A/B screenshot proof.

Test Scene

• Project: D:\code\teach-me\test-scene
• PBR assets: test-scene/assets/polyhaven/ (Barrel_01, Camera_01, Lantern_01 — 1K textures)
• Shaders: test-scene/shaders/ (copied from library/godot-gamedev/reference/code/)
• Screenshot output: test-scene/.scratch/screenshots/

glTF Import Fix

MCP reimport/scan do NOT trigger Godot's scene importer for glTF files. If .gltf.import shows valid=false:

1. Delete the .gltf.import files
2. Run godot --headless --editor --import --quit --path test-scene
3. Restart the editor (quit + relaunch)
4. Then node_create with scene_path will work

Capturing Screenshots to Disk

editor_screenshot returns inline base64 only — cannot save to files. To get files:

1. Run the project (project_run)
2. Use game_eval to position camera, toggle shader, and save:

var img = get_viewport().get_texture().get_image()
img.save_png('user://screenshots/filename.png')

Files land at C:/Users/uosmi/AppData/Roaming/Godot/app_userdata/teach-me-shader-test/screenshots/. Copy to test-scene/.scratch/screenshots/ after capture.

Framing Objects (Fill the Frame)

Calculate camera distance from object AABB so it occupies ~80% of viewport:

var half_fov_tan = tan(cam.fov * 0.5 * PI / 180.0)
var dist = largest_aabb_dimension / half_fov_tan

Position camera at target + offset where offset uses 30° elevation/azimuth:

var elev = 30.0 * PI / 180.0
var azim = 30.0 * PI / 180.0
var offset = Vector3(dist * cos(elev) * sin(azim), dist * sin(elev), dist * cos(elev) * cos(azim))
cam.global_position = target + offset
cam.look_at(target)

MCP Reliability (hard rules — validated 2026-08-26)

The godot-ai MCP has three failure modes that cause silent wrong results:

1. game_eval mutations are for READING, not persisting. Setting rotation_degrees or set_shader_parameter on a running instance is unreliable — changes may not affect the render or reset on the next project_run. Symptom: two different "edits" produce pixel-identical captures. Fix: edit the .tscn on disk (persistent, git-tracked), then project_run picks up saved state. Use game_eval only to capture the viewport and sample pixels.