Real Windows for Kerbal Space Program 1.12

Features

• Interiors shown through windows. In flight, the windows of every crewed part show its interior (IVA) from outside.
• No configuration, any part. Windows are found automatically from each part's own textures and interior, so stock and modded parts work out of the box.
• Glass windows. Reflections at grazing angles, a sun glint and faint smudges to simulate a glass layer.
• All vessels in view. All vessels within range show their interiors, even when not the active vessel.
• Open hatches look through. With FreeIva installed, an open hatch shows the next part's interior through the hatch.
• Optimized. Interiors are rendered only where a window is actually on screen, only over that area, and the static cabin is cached between camera moves; crew still animate every frame. Alt+F8 switches the mod off and on in flight. Expect around 10-15% less FPS with the mod active. (The stock "Show Interiors" option is about twice as expensive!)

Requires KSP 1.12.x. Optional: FreeIva. Shaders are included for Windows, macOS and Linux; only Windows has been tested in game so far. Licence: GPL v3.

How it works

• Finding the windows (once per part type). The hull is drawn flat into its texture's UV space and read back. Candidate panes are the regions its lightmap or gloss map marks; each is kept only if the IVA, seen from the crew seats, really has an opening behind it. Kept regions take their exact outline from the UV island or the glass-coloured paint, and the result is a cached window mask per texture. Glass sub-meshes and window-named meshes are handled directly. A per-pixel interior probe is the fallback for parts with no usable texture information.
• Keeping interiors aligned. KSP places each interior once, frozen at the design pose and relative to the active vessel. To keep the interiors aligned, it builds the exact rigid map from each part's live transform to its interior's current placement and renders through it. Nothing is moved, so stock IVA is untouched.
• Four passes per frame, from the flight camera:
• the hulls, writing part id, depth, window state and the glass surface;
• the interior shells only, to know whose interior each pixel sees;
• a real camera on the interiors, cropped to the windows' screen area;
• a composite blending interior and glass into the scene where it's a window.
• Caching. The cabin shell and props are rendered into a cached colour and depth image, redrawn only when the view of them changes (or about once a second for lights and screens). Kerbals are drawn over it every frame, depth-tested against the cache.
• Neighbours and inside views. Parts behind open hatches are drawn in the same render, so their interior counts as seen. From inside a part, the composite runs a second time after clouds and atmosphere.