editor: tile paint and collision strokes are one undo step, no collision option for tiles (visual-only model copy in the build), freed gl buffers and stale pick ids, export level as gltf/glb with textures and vertex colours

docs/manual/06-geometry.md

@@ -267,6 +267,8 @@ used in the level** hides unused ones. Click a model to make it the current one,
 Painting onto a tile at the same height **swaps its model** instead of stacking a second tile.
 New tiles copy the vertex colours of an existing tile with the same model.
 
+One drag is one undo step: **Ctrl+Z** brings back all tiles a stroke painted over, erased or swapped.
+
 > **Tip:** Prefer swapping, moving or hiding original tiles over erasing them. Object scripts can
 > address tiles by their number, and erasing a tile shifts the numbers of all later tiles. The
 > status bar warns you when you erase an original tile.
@@ -326,7 +328,15 @@ change all tiles** (paint the model, every tile using it changes) or **Shared mo
 this tile** (the painted tile gets its own copy of the model first).
 
 Brushes have one material per face class (top, sides, bottom); tile models are painted per
-polygon. Tile collision cannot be switched off – paint it 30 or hide the tile instead.
+polygon. A painting drag is one undo step.
+
+### Tiles without collision
+
+To make a tile only visual, select it and tick **No collision** (Inspector, section **Build**; works
+for several selected tiles at once). The built level then uses a copy of the tile's model without
+collision polygons: the llama walks through the tile (a wall) or falls through it (a floor). Other
+tiles of the same model keep their collision. In the editor the tile no longer shows collision
+lines, and checks such as "no floor under the player start" ignore it.
 
 The layer **Invisible collision volumes** draws invisible walls, invisible blocks and colliders
 translucent red so you can see them while editing.

docs/manual/07-meshes.md

@@ -7,7 +7,7 @@ collision and lit vertex colours, and its textures are packed onto texture pages
 
 The **library** works the other way round: it saves geometry from any level (original tiles,
 brushes and meshes, with their textures) so you can insert it into other levels. And **Export
-selection as OBJ** takes level geometry to Blender.
+selection as OBJ** takes level geometry to Blender, **Export level as glTF** the whole level.
 
 ## Supported files
 
@@ -178,6 +178,28 @@ it in Blender, then **File → Import mesh** it back (round trip).
 > **Note:** The exported textures are game data – fine for your own editing, please don't share
 > them.
 
+## Export the level as glTF
+
+**File → Export level as glTF…** writes the whole level – tiles, brushes and meshes – as one glTF
+2.0 file for Blender or any 3D viewer:
+
+* **.glb** (binary) or **.gltf** (text, everything in one file), chosen by the file type,
+* the level's texture pages as PNG pictures inside the file, the game's vertex colours
+  (light and shade) as vertex colours, transparent and double-sided parts as such,
+* unlit materials, so viewers show the baked colours like the game.
+
+| Option | Meaning |
+|---|---|
+| **Object models** | also the models of placed objects (coins, characters …) as the viewport shows them |
+| **Leave out hidden items** | items hidden in the editor (**H**) are not exported |
+| **Game orientation** | mirrors the level so that Blender and viewers show it the same way round as the game. Off: the same axes as the OBJ export and **Import mesh**, so the file can be imported again unchanged |
+
+Tiles with **Exclude from build** are left out. 1 unit is 1 cell.
+
+![glTF export dialog and the exported village read back by Import mesh](img/geo_gltf_export.jpg)
+
+> **Note:** The exported textures are game data – fine for your own use, please don't share them.
+
 ## Tips for good meshes
 
 * Model at the right scale: 1 cell is one grid square, the llama is about 0.6 cells tall. Use

docs/manual/19-shortcuts.md

@@ -157,6 +157,7 @@ Every menu command with its shortcut and a short description.
 | Import texture… |  | Import PNG/JPG images as textures (colour reduction, blend class, packing) |
 | Export level WAD… |  | Build the level and save the game file (.wad) somewhere |
 | Export selection as OBJ… |  | Mesh, UVs, vertex colours, textures (PNG) and collision for Blender |
+| Export level as glTF… |  | The whole level with textures and vertex colours as .glb / .gltf (Blender, viewers) |
 | Close editor | **Ctrl+Q** | Close the editor |
 
 ### Edit menu