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, 101 insertions, 0 deletions

diff --git a/src/engine/input.cpp b/src/engine/input.cpp
new file mode 100644
index 0000000..ffa8076
--- /dev/null
+++ b/src/engine/input.cpp
@@ -0,0 +1,101 @@
+#include "engine/input.hpp"
+#include "imgui_impl_sdl3.h"
+
+void Input::begin_frame() {
+    // Save previous state
+    for (int i = 0; i < SDL_SCANCODE_COUNT; i++) {
+        key_prev_[i] = key_state_[i];
+        key_just_pressed_[i]  = false;
+        key_just_released_[i] = false;
+    }
+    mouse_prev_ = mouse_pos_;
+    mouse_delta_ = glm::vec2(0.0f);
+    scroll_ = 0.0f;
+    for (int i = 0; i < 8; i++) {
+        mouse_prev_state_[i] = mouse_state_[i];
+        mouse_pressed_[i]  = false;
+        mouse_released_[i] = false;
+    }
+
+    // Pump SDL events
+    SDL_Event event;
+    while (SDL_PollEvent(&event)) {
+        ImGui_ImplSDL3_ProcessEvent(&event);   // let the dev UI see input too
+        switch (event.type) {
+        case SDL_EVENT_QUIT:
+            quit_ = true;
+            break;
+
+        case SDL_EVENT_KEY_DOWN: {
+            auto sc = event.key.scancode;
+            if (sc < SDL_SCANCODE_COUNT) {
+                if (!key_state_[sc]) key_just_pressed_[sc] = true;
+                key_state_[sc] = true;
+            }
+            break;
+        }
+        case SDL_EVENT_KEY_UP: {
+            auto sc = event.key.scancode;
+            if (sc < SDL_SCANCODE_COUNT) {
+                key_just_released_[sc] = true;
+                key_state_[sc] = false;
+            }
+            break;
+        }
+
+        case SDL_EVENT_MOUSE_MOTION:
+            mouse_pos_ = glm::vec2(event.motion.x, event.motion.y);
+            mouse_delta_ = glm::vec2(event.motion.xrel, event.motion.yrel);
+            break;
+
+        case SDL_EVENT_MOUSE_BUTTON_DOWN:
+            if (event.button.button < 8) {
+                if (!mouse_state_[event.button.button])
+                    mouse_pressed_[event.button.button] = true;
+                mouse_state_[event.button.button] = true;
+            }
+            break;
+        case SDL_EVENT_MOUSE_BUTTON_UP:
+            if (event.button.button < 8) {
+                mouse_released_[event.button.button] = true;
+                mouse_state_[event.button.button] = false;
+            }
+            break;
+
+        case SDL_EVENT_MOUSE_WHEEL:
+            scroll_ = event.wheel.y;
+            break;
+
+        default:
+            break;
+        }
+    }
+}
+
+bool Input::key_down(SDL_Keycode key) const {
+    return key_state_[SDL_GetScancodeFromKey(key, nullptr)];
+}
+
+bool Input::key_pressed(SDL_Keycode key) const {
+    return key_just_pressed_[SDL_GetScancodeFromKey(key, nullptr)];
+}
+
+bool Input::key_released(SDL_Keycode key) const {
+    return key_just_released_[SDL_GetScancodeFromKey(key, nullptr)];
+}
+
+glm::vec2 Input::mouse_pos() const   { return mouse_pos_; }
+glm::vec2 Input::mouse_delta() const { return mouse_delta_; }
+float Input::scroll_delta() const    { return scroll_; }
+
+bool Input::mouse_down(int button) const {
+    return button < 8 && mouse_state_[button];
+}
+
+bool Input::mouse_pressed(int button) const {
+    return button < 8 && mouse_pressed_[button];
+}
+
+bool Input::mouse_released(int button) const {
+    return button < 8 && mouse_released_[button];
+}