Initial import: LibreForts (M0-M5 in progress)

Open-source Forts clone: custom C++20 engine + data-driven (Lua) 2D physics
artillery RTS.

- Building: node/strut graph on a stiff mass-spring solver (canon Forts model),
  triangulation rigidity, axial + 30-degree angle-stress breaking, cascading
  collapse, fire (DoT + spread), ground destroys debris.
- Weapons (M4): cannon (ballistic) + laser (beam/ignite) with select-and-aim-in-
  arc UX; splash / beam damage; bg-brace passthrough.
- Devices + economy (M5): reactors + win/loss + restart, mines/turbines/battery,
  metal deposits, storage caps, per-shot energy cost.
- Data-driven via Lua/sol2 with a layered mod loader; enemy-fort scenario mod.
- Renderer: SDL3 + textures + ImGui dev UI. stb_image + ImGui vendored.
- Assets: CC0 placeholders only; real game art loaded at runtime from the user's
  own install via forts: paths (bring-your-own; nothing copyrighted committed).

See README.md / CLAUDE.md and research/ + requirements/ for detail.

1 files changed, 32 insertions, 0 deletions

diff --git a/src/game/build_system.hpp b/src/game/build_system.hpp
new file mode 100644
index 0000000..0bf615d
--- /dev/null
+++ b/src/game/build_system.hpp
@@ -0,0 +1,32 @@
+#pragma once
+
+// Material types for building.
+enum class Material : int {
+    Wood          = 0,
+    Background    = 1,
+    Rope          = 2,
+    COUNT         = 3,
+};
+
+struct MaterialInfo {
+    const char* name;
+    float half_w, half_h;   // half-size of placed piece
+    float metal_cost;
+    float energy_cost;
+    float r, g, b;          // color
+    float alpha;            // 1.0 = opaque, 0.4 = semi-transparent
+    bool  blocks_projectiles;
+};
+
+inline MaterialInfo material_info(Material m) {
+    switch (m) {
+    case Material::Wood:
+        return {"Wood", 1.0f, 0.4f, 10.0f, 5.0f, 0.55f, 0.35f, 0.15f, 1.0f, true};
+    case Material::Background:
+        return {"BgBrace", 1.0f, 0.4f, 5.0f, 3.0f, 0.45f, 0.40f, 0.30f, 0.4f, false};
+    case Material::Rope:
+        return {"Rope", 0.0f, 0.0f, 3.0f, 2.0f, 0.15f, 0.12f, 0.10f, 1.0f, false};
+    default:
+        return {"???", 1.0f, 0.4f, 0.0f, 0.0f, 1.0f, 0.0f, 1.0f, 1.0f, true};
+    }
+}