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, 53 insertions, 0 deletions

diff --git a/src/engine/input.hpp b/src/engine/input.hpp
new file mode 100644
index 0000000..764ca96
--- /dev/null
+++ b/src/engine/input.hpp
@@ -0,0 +1,53 @@
+#pragma once
+
+#include <SDL3/SDL.h>
+#include <glm/glm.hpp>
+
+// Simple polling-based input state. Call begin_frame() once per frame,
+// then query state during update.
+
+class Input {
+public:
+    // Call once per frame BEFORE reading any input state.
+    // Processes the SDL event queue and updates internal state.
+    void begin_frame();
+
+    // Keyboard
+
+    bool key_down(SDL_Keycode key) const;
+    bool key_pressed(SDL_Keycode key) const;   // true only on the frame it went down
+    bool key_released(SDL_Keycode key) const;  // true only on the frame it went up
+
+    // Mouse
+
+    glm::vec2 mouse_pos() const;         // in window coordinates
+    glm::vec2 mouse_delta() const;       // movement since last frame
+    float scroll_delta() const;          // vertical scroll (positive = scroll up)
+
+    bool mouse_down(int button) const;   // SDL_BUTTON_LEFT, MIDDLE, RIGHT
+    bool mouse_pressed(int button) const;
+    bool mouse_released(int button) const;
+
+    // Window
+
+    bool quit_requested() const { return quit_; }
+
+private:
+    // Keyboard
+    bool key_state_[SDL_SCANCODE_COUNT] = {};
+    bool key_prev_[SDL_SCANCODE_COUNT] = {};
+    bool key_just_pressed_[SDL_SCANCODE_COUNT] = {};
+    bool key_just_released_[SDL_SCANCODE_COUNT] = {};
+
+    // Mouse
+    glm::vec2 mouse_pos_   = {0.0f, 0.0f};
+    glm::vec2 mouse_prev_  = {0.0f, 0.0f};
+    glm::vec2 mouse_delta_ = {0.0f, 0.0f};
+    float scroll_          = 0.0f;
+    bool  mouse_state_[8]       = {};
+    bool  mouse_prev_state_[8]  = {};
+    bool  mouse_pressed_[8]     = {};
+    bool  mouse_released_[8]    = {};
+
+    bool quit_ = false;
+};