Recoil and armor

10 files changed, 128 insertions, 35 deletions

diff --git a/CLAUDE.md b/CLAUDE.md
index a2453f7..23aec69 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -155,8 +155,9 @@ See `requirements/milestones.org` for the live checklist. Roughly:
   destruction (stress/collapse/fire).
 - **M4 mostly done:** per-strut HP, cannon (ballistic) + laser (beam/fire) with
   the Forts select-a-weapon-and-aim-in-its-arc UX, direct-vs-splash delivery,
-  fire + spread. Missing: mortar, flak/point-defence, machinegun/sniper
-  (hitscan), guided missiles, EMP, per-shot recoil, metal-per-shot.
+  fire + spread, firing recoil, and the armour material (build mode 4).
+  Missing: mortar, flak/point-defence, machinegun/sniper (hitscan), guided
+  missiles, EMP, metal-per-shot.
 - **M5 mostly done:** reactors + win/loss + restart (R), real resource economy
   (mines on deposits, turbines by height, storage caps, firing costs energy),
   device framework + placement. Two gaps: fire does **not** damage devices, and
diff --git a/data/materials.lua b/data/materials.lua
index 3725aa9..b88a1da 100644
--- a/data/materials.lua
+++ b/data/materials.lua
@@ -1,7 +1,7 @@
 -- Base building materials for the clone.
 --
--- The engine reads the global `Materials` array (in order). Build modes 1/2/3
--- map to entries 1/2/3. Mods under data/mods/ run AFTER this file and may use
+-- The engine reads the global `Materials` array (in order). Build modes 1-4
+-- map to entries 1-4. Mods under data/mods/ run AFTER this file and may use
 -- FindMaterial(name) to tweak these, or table.insert(Materials, ...) to add new
 -- ones. (angle_threshold is in DEGREES; the engine converts to radians.)
 
@@ -17,6 +17,7 @@ Materials =
         flammable = true, burn_rate = 15, spread_time = 2.0,   -- wood: slow burn/spread
         blocks_projectiles = true, blocks_beam = true,         -- solid: stops shells & beams
         half_width = 0.15,
+        cost_metal = 5, cost_energy = 25,               -- Forts wood 0.1 / 0.5
         color = { 1.0, 1.0, 1.0, 1.0 },                 -- white = show texture untinted
         texture = "data/textures/wood.png",
         texture_forts = "forts:materials/wood_panel.tga",
@@ -31,6 +32,7 @@ Materials =
         flammable = true, burn_rate = 22, spread_time = 0.7,   -- burns ~3x faster than wood
         blocks_projectiles = false, blocks_beam = false,       -- shells AND beams pass through (beam still burns it)
         half_width = 0.15,
+        cost_metal = 5, cost_energy = 25,
         color = { 1.0, 1.0, 1.0, 0.45 },                -- translucent
         texture = "data/textures/bgbrace.png",
         texture_forts = "forts:materials/bracing-bg.tga",
@@ -45,10 +47,31 @@ Materials =
         flammable = true, burn_rate = 25, spread_time = 1.0,   -- burns through fast
         blocks_projectiles = false, blocks_beam = false,       -- shells AND beams pass through
         half_width = 0.04,
+        cost_metal = 5, cost_energy = 25,
         color = { 0.72, 0.66, 0.55, 1.0 },   -- tan: tints the cable art, and is
                                              -- the visible rope when it is absent
         texture_forts = "forts:materials/cable.tga",
     },
+    -- Appended LAST on purpose: build modes map to this array by index, so a new
+    -- material goes on the end (key 4) rather than shifting bg-brace and rope.
+    {
+        name = "armour",                                -- the kinetic tank
+        -- Forts armor: 25% stiffer than wood, 2x the mass, HP 400, and it does
+        -- NOT catch fire (its Fire deg/s is n/a). 3 wood (450 HP) still beats
+        -- 1 armour (400 HP), so armour buys durability per strut, not per metal.
+        stiffness = 750, damping = 12, mass = 0.5,
+        max_compression = 0.90, max_expansion = 1.10,   -- same +/-10% as wood
+        angle_threshold = 30, tension_only = false,
+        min_length = 0.4, max_length = 3.0, max_link_length = 6.0,
+        hit_points = 400,
+        flammable = false, burn_rate = 0, spread_time = 0,   -- metal: never burns
+        blocks_projectiles = true, blocks_beam = true,       -- solid
+        half_width = 0.18,                              -- reads chunkier than wood
+        cost_metal = 90, cost_energy = 75,              -- Forts 1.8 / 1.5, i.e.
+                                                        -- 18x wood metal, 3x energy
+        color = { 0.62, 0.66, 0.70, 1.0 },              -- steel (also the fallback)
+        texture_forts = "forts:materials/armor.tga",
+    },
 }
 
 -- Helpers mods can use (mirrors the Forts modding API shape).
diff --git a/data/weapons.lua b/data/weapons.lua
index a6e23d5..98b7464 100644
--- a/data/weapons.lua
+++ b/data/weapons.lua
@@ -15,6 +15,8 @@ Weapons =
         min_fire_angle = -20,         -- firing arc (degrees, rel. to mount) — Forts MinFireAngle
         max_fire_angle = 30,          -- Forts MaxFireAngle
         energy_cost = 120,            -- energy per shot (Forts EnergyFireCost)
+        recoil = 12,                  -- kick shoved back into the firing fort
+                                      -- (Forts Recoil). Tune in the Dev panel.
         texture = "data/textures/weapon_turret.png",
         projectile_texture = "data/textures/projectile_laser.png",
         texture_forts = "forts:weapons/cannon/base.tga",
@@ -31,6 +33,7 @@ Weapons =
         min_fire_angle = -20,         -- Forts laser MinFireAngle -20
         max_fire_angle = 45,          -- Forts laser MaxFireAngle 45
         energy_cost = 200,            -- beam is energy-hungry
+        recoil = 0,                   -- a beam has no kickback
         texture = "data/textures/weapon_turret.png",
         texture_forts = "forts:weapons/beamlaser/base.tga",
     },
diff --git a/requirements/milestones.org b/requirements/milestones.org
index 3aeb4a9..a2cabe8 100644
--- a/requirements/milestones.org
+++ b/requirements/milestones.org
@@ -130,7 +130,8 @@ This is the purely-structural half of Forts destruction (no weapons yet).
       the ground surface is removed (+ explosion puff), taking its edges with it
 - [X] Disconnection -> fall -> destroy: a chunk that loses its path to a
       foundation simply falls under gravity and dies on the ground
-- [X] Materials: wood, background bracing, ropes (tension-only)
+- [X] Materials: wood, background bracing, ropes (tension-only), armour
+      (HP 400, 25% stiffer, 2x mass, never burns -- build mode 4)
 - [X] Per-strut HP pool (separate from stress) -- delivered in M4
 - [X] Fire (damage-over-time, strut-to-strut spread) -- delivered in M4
 
@@ -153,10 +154,13 @@ models (per-strut HP and radius splash) plus fire.
 - [X] Fire system: ignition flag, damage-over-time, spread along the graph,
       burns background bracing faster (the counter to the bg-brace trick)
 
+- [X] Firing recoil: each shot shoves the FIRING structure back along -aim
+      (=BuildGraph::apply_recoil=, per-weapon =recoil= in data/weapons.lua;
+      the beam laser has none). Tunable live in the Dev panel.
+
 Still missing from the vanilla roster / mechanics (see gameplay-gaps.org #5, #8):
 mortar, flak + point-defence, machinegun/sniper (hitscan), guided swarm
-missiles, EMP, and per-shot RECOIL on the firing structure (we apply knockback
-to targets only).
+missiles, EMP, and the per-shot METAL cost (only energy is charged).
 
 * M5: Reactor, Resources & Game Loop  [MOSTLY DONE]
 
@@ -172,7 +176,10 @@ Goal: There's a reactor to destroy, and a real economy to build it with.
       surviving =is_core= device. The collapse path needs devices mounted on
       the graph (see M6 / gameplay-gaps.org #3).
 - [X] Resource system (deferred from M2): mines on metal deposits, wind
-      turbines for energy, generation rates, storage caps, build/fire costs
+      turbines for energy, generation rates, storage caps, build/fire costs.
+      Build costs are now PER-MATERIAL (=cost_metal= / =cost_energy= in
+      data/materials.lua) and enforced -- you cannot place a strut you cannot
+      afford, which is what makes armour's 18x metal price a real choice.
 - [X] Win/lose condition + restart (R key)
 
 * M6: Dummy Fort & Map  [PARTIAL]
diff --git a/research/gameplay-gaps.org b/research/gameplay-gaps.org
index c6d1b17..fb02b4f 100644
--- a/research/gameplay-gaps.org
+++ b/research/gameplay-gaps.org
@@ -35,6 +35,9 @@ Since the first draft of this document we also have:
   restart on R.
 - *Bring-your-own Forts art*: =texture_forts= paths load real sprites from the
   player's own install, falling back to the CC0 placeholders.
+- *Armour* (build mode 4): HP 400, 25% stiffer, 2x mass, never burns.
+- *Per-material build costs*, enforced: you cannot place what you cannot afford.
+- *Firing recoil*: a shot shoves the firing structure back, not just the target.
 
 * MISSING — grouped by system, each with the in-game reference
 
@@ -100,9 +103,12 @@ swarm missiles (guided), missile launcher, 20mm cannon, cannon, flak
 (beam). Notable *mechanics* we lack: point-defence (shoot down incoming shells),
 guided/tracking projectiles, hitscan (machinegun/sniper), EMP disable.
 
-** 6. Building materials we lack
-=materials/building_materials.lua=: *armour* (HP 400, +25% stiffness, 2x mass —
-kinetic tank), *door* (openable/closable, blocks then opens for your own fire),
+** 6. Building materials we lack  [PARTIAL — armour landed]
+DONE: *armour* (HP 400, +25% stiffness, 2x mass, does not burn, 18x wood's metal
+cost) is build mode 4. The rest of this list still stands.
+
+=materials/building_materials.lua=: *door* (openable/closable, blocks then opens
+for your own fire),
 *energy shield* (reflects beams/plasma, warmup), *metal beam*, *camo*, *solar*
 (energy on the strut), *fuse* (relays fire slowly). We have wood/bg/rope only.
 Doors and shields are real tactical mechanics (open to shoot, shield vs lasers).
@@ -117,8 +123,10 @@ Doors and shields are real tactical mechanics (open to shoot, shield vs lasers).
 - Cannon/weapons cost energy+metal PER SHOT (EnergyFireCost) — firing is
   resource-limited, not just reload-limited. DONE for energy (=energy_cost= per
   weapon); the per-shot METAL cost is still missing.
-- Recoil/kickback pushes the fort (we apply knockback to targets only, not
-  recoil to the firing structure — Forts Recoil 600000, KickbackMean 40).
+- Recoil/kickback pushes the fort — DONE: each shot applies a velocity kick to
+  the firing structure along -aim (=BuildGraph::apply_recoil=), separate from the
+  knockback dealt to targets. Per-weapon =recoil= in data, tunable in the Dev
+  panel; the beam laser has none.
 - Spotters: sniper reveals targets and guides swarm missiles.
 - Fire-clearance: a weapon won't fire if its own structure blocks the muzzle
   (MinFireClearance) — prevents shooting through your own fort.
@@ -148,8 +156,9 @@ Mapping the above onto the (already-reordered) milestones:
 | Resource economy (mine/turbine/store) | M5        | DONE (no mine2/turbine2/store) |
 | Per-shot energy cost                  | M4        | DONE (metal-per-shot missing)  |
 | Devices framework (mount on struts)   | M5/M6     | not mounted on strut graph     |
-| Armour + Door + Shield materials      | M4/M7     | data-driven, small each        |
-| Firing recoil on the shooter          | M4        | small, faithful, not started   |
+| Armour material                       | M4/M7     | DONE (build mode 4)            |
+| Firing recoil on the shooter          | M4        | DONE (per-weapon, in data)     |
+| Door + Shield materials               | M7        | need mechanics, not just data  |
 | More weapons (mortar/flak/mg/missile) | M4        | point-defence + guided are new |
 | Repair + Recycle                      | M7        | resource-cost actions          |
 | Tech tree + Upgrades                  | post-v0.1 | big; build-order strategy      |
@@ -159,21 +168,19 @@ Mapping the above onto the (already-reordered) milestones:
 
 * Smallest high-value next steps (concrete)
 
-Items 1 and 2 of the original list (reactor + win/loss, real resources) are DONE;
-what follows is the refreshed queue.
+Reactor + win/loss, real resources, armour and firing recoil are all DONE; what
+follows is the refreshed queue.
 
-1. *Armour material*: data-only addition to =data/materials.lua= (Forts armour is
-   HP 400, +25% stiffness, 2x mass). The material system already has every field
-   it needs, and =materials/armor.tga= is a TGA, so =texture_forts= picks up the
-   real sprite for free. Cheapest real gameplay depth available.
-2. *Firing recoil*: apply an impulse to the FIRING structure, not just the target
-   (Forts Recoil 600000, KickbackMean 40). The knockback machinery already
-   exists; this is a few lines and makes combat feel like Forts.
-3. *Mount devices on the strut graph*: attach devices to nodes so cutting the
+1. *Mount devices on the strut graph*: attach devices to nodes so cutting the
    supports drops them. Unlocks the second victory path in #1 and makes reactors
-   killable by collapse, which is a signature Forts moment.
-4. *Door material*: toggles =blocks_projectiles= so you can open to shoot and
+   killable by collapse, a signature Forts moment. This one root cause blocks
+   three separate gaps, so it buys the most per unit of work.
+2. *Fire damages devices*: Forts burns devices at 2.5 hp/s, 5x the 0.5 hp/s it
+   does to struts. We do not damage devices with fire at all.
+3. *Door material*: toggles =blocks_projectiles= so you can open to shoot and
    close to tank. Needs a small mechanic, not just data.
-5. *Mortar or flak*: the next weapons. Flak brings a genuinely new mechanic
+4. *Mortar or flak*: the next weapons. Flak brings a genuinely new mechanic
    (point-defence intercepting incoming shells); mortar is a high-arc,
    high-building-damage counterpart to the cannon.
+5. *Per-shot metal cost*: firing charges energy but not metal (Forts charges
+   both). A one-line data + deduction change.
diff --git a/src/engine/app.cpp b/src/engine/app.cpp
index d5001c1..2108316 100644
--- a/src/engine/app.cpp
+++ b/src/engine/app.cpp
@@ -226,6 +226,7 @@ void App::run() {
         if (input.key_pressed(SDLK_1)) { cur_mat = 0; selected_cannon = -1; place_dev = -1; }
         if (input.key_pressed(SDLK_2)) { cur_mat = 1; selected_cannon = -1; place_dev = -1; }
         if (input.key_pressed(SDLK_3)) { cur_mat = 2; selected_cannon = -1; place_dev = -1; }
+        if (input.key_pressed(SDLK_4)) { cur_mat = 3; selected_cannon = -1; place_dev = -1; }
         if (input.key_pressed(SDLK_5)) { place_dev = turbine_i; selected_cannon = -1; }
         if (input.key_pressed(SDLK_6)) { place_dev = mine_i;    selected_cannon = -1; }
         if (input.key_pressed(SDLK_7)) { place_dev = battery_i; selected_cannon = -1; }
@@ -279,6 +280,10 @@ void App::run() {
                         wpn.splash_damage, wpn.splash_radius, wpn.knockback,
                         wpn.projectile_radius, 6.0f, wpn.fire_chance });
                 }
+                // Recoil: shove the firing structure back along -aim. Radius
+                // picks up the nodes the weapon is sitting on.
+                graph.apply_recoil(c.x, c.y, 1.5f,
+                                   -std::cos(c.aim), -std::sin(c.aim), wpn.recoil);
                 c.cooldown = wpn.reload;
                 energy -= wpn.energy_cost;
             }
@@ -333,22 +338,29 @@ void App::run() {
         // ---- Finish edge placement ---- (add_link enforces the length rules
         //      and subdivides a long drag into segments)
         if (placing && !input.mouse_down(SDL_BUTTON_LEFT)) {
+            const auto& m = graph.materials[cur_mat];
+            // Per-material cost, and you must be able to afford it. Without the
+            // affordability check an expensive material (armour) would be free
+            // whenever you are broke, since resources are clamped back to 0.
+            bool can_pay = metal >= m.cost_metal && energy >= m.cost_energy;
             int target = graph.find_nearest_node(wx, wy, 0.5f);
             if (target >= 0 && target != drag_node) {
-                if (graph.add_link(drag_node, target, cur_mat) > 0) {
-                    metal -= 5.0f; energy -= 25.0f;
+                if (can_pay && graph.add_link(drag_node, target, cur_mat) > 0) {
+                    metal -= m.cost_metal; energy -= m.cost_energy;
                 }
             } else if (drag_node >= 0 && drag_node < (int)graph.nodes.size()) {
                 bool foundation = graph.is_on_ground(wy);
                 float ny = foundation ? graph.ground_level : wy;
                 // Length guard first, so a rejected link leaves no orphan node.
-                const auto& m = graph.materials[cur_mat];
                 float dlen = std::hypot(wx - graph.nodes[drag_node].x,
                                         ny - graph.nodes[drag_node].y);
-                if (dlen >= m.min_length && dlen <= m.max_link_length) {
+                // A foundation node costs extra on top of the strut.
+                bool pay_all = metal  >= m.cost_metal  + (foundation ? 50.0f  : 0.0f) &&
+                               energy >= m.cost_energy + (foundation ? 400.0f : 0.0f);
+                if (pay_all && dlen >= m.min_length && dlen <= m.max_link_length) {
                     int new_id = graph.add_node(wx, ny, foundation);
                     if (graph.add_link(drag_node, new_id, cur_mat) > 0) {
-                        metal -= 5.0f; energy -= 25.0f;
+                        metal -= m.cost_metal; energy -= m.cost_energy;
                         if (foundation) { metal -= 50.0f; energy -= 400.0f; }
                     }
                 }
@@ -361,9 +373,14 @@ void App::run() {
         if (extruding_edge >= 0 && !input.mouse_down(SDL_BUTTON_RIGHT)) {
             float offx = wx - extrude_start_x;
             float offy = wy - extrude_start_y;
-            if (std::sqrt(offx*offx + offy*offy) > 0.1f) {
+            // An extrusion sweeps out several struts, so it costs 2x the
+            // material's metal (for wood that is the flat 10/25 it used before).
+            const auto& em = graph.materials[cur_mat];
+            float ex_metal = em.cost_metal * 2.0f, ex_energy = em.cost_energy;
+            if (std::sqrt(offx*offx + offy*offy) > 0.1f &&
+                metal >= ex_metal && energy >= ex_energy) {
                 graph.extrude_edge(extruding_edge, offx, offy);
-                metal -= 10.0f; energy -= 25.0f;
+                metal -= ex_metal; energy -= ex_energy;
             }
             extruding_edge = -1;
         }
@@ -759,6 +776,10 @@ void App::run() {
             if (ImGui::Button("wood"))    { cur_mat = 0; place_dev = -1; selected_cannon = -1; }
             ImGui::SameLine(); if (ImGui::Button("bg")) { cur_mat = 1; place_dev = -1; selected_cannon = -1; }
             ImGui::SameLine(); if (ImGui::Button("rope")) { cur_mat = 2; place_dev = -1; selected_cannon = -1; }
+            if ((int)graph.materials.size() > 3) {
+                ImGui::SameLine();
+                if (ImGui::Button("armour")) { cur_mat = 3; place_dev = -1; selected_cannon = -1; }
+            }
             if (turbine_i >= 0 && ImGui::Button("turbine")) { place_dev = turbine_i; selected_cannon = -1; }
             if (mine_i >= 0) { ImGui::SameLine(); if (ImGui::Button("mine")) { place_dev = mine_i; selected_cannon = -1; } }
             if (battery_i >= 0) { ImGui::SameLine(); if (ImGui::Button("battery")) { place_dev = battery_i; selected_cannon = -1; } }
@@ -787,6 +808,7 @@ void App::run() {
                     ImGui::PushID(&wpn);
                     if (ImGui::TreeNode(wpn.name.c_str())) {
                         ImGui::SliderFloat("reload", &wpn.reload, 0.1f, 6.0f);
+                        ImGui::SliderFloat("recoil", &wpn.recoil, 0.0f, 60.0f);
                         if (wpn.is_beam) {
                             ImGui::SliderFloat("beam_dps",      &wpn.beam_dps,      10.0f, 300.0f);
                             ImGui::SliderFloat("beam_duration", &wpn.beam_duration, 0.2f,  4.0f);
diff --git a/src/game/build_graph.cpp b/src/game/build_graph.cpp
index 032bbf5..a1195af 100644
--- a/src/game/build_graph.cpp
+++ b/src/game/build_graph.cpp
@@ -291,6 +291,21 @@ int BuildGraph::kill_grounded() {
 // Destruction
 // =============================================================================
 
+void BuildGraph::apply_recoil(float x, float y, float radius,
+                              float dx, float dy, float strength) {
+    if (radius <= 0.0f || strength <= 0.0f) return;
+
+    for (auto& n : nodes) {
+        if (n.is_foundation) continue;   // pinned: the ground eats the recoil
+        float ox = n.x - x, oy = n.y - y;
+        float d = std::sqrt(ox*ox + oy*oy);
+        if (d >= radius) continue;
+        float f = 1.0f - d / radius;     // linear falloff, as in apply_splash
+        n.vx += dx * strength * f;
+        n.vy += dy * strength * f;
+    }
+}
+
 void BuildGraph::apply_splash(float x, float y, float radius, float damage,
                              float knockback) {
     if (radius <= 0.0f) return;
diff --git a/src/game/build_graph.hpp b/src/game/build_graph.hpp
index bf83a18..4452139 100644
--- a/src/game/build_graph.hpp
+++ b/src/game/build_graph.hpp
@@ -34,6 +34,8 @@ struct MaterialDef {
     bool  blocks_projectiles; // stops cannon shells (wood yes; bg-brace/rope no)
     bool  blocks_beam;        // stops laser beams (all yes in Forts)
     float half_width;       // visual thickness
+    float cost_metal;       // metal spent placing one strut of this material
+    float cost_energy;      // energy spent placing one strut of this material
     float r, g, b, a;       // visual colour (also tints the texture)
     std::string name;
     std::string texture;    // CC0 placeholder path ("" = flat colour)
@@ -104,6 +106,13 @@ public:
     // not block splash (pure radius falloff, like Forts AoE).
     void apply_splash(float x, float y, float radius, float damage, float knockback);
 
+    // Directional velocity kick to free nodes within `radius` of (x,y), along the
+    // unit vector (dx,dy), with linear falloff. Weapon recoil uses this to shove
+    // the FIRING structure back (Forts' Recoil), unlike apply_splash's radial
+    // knockback on the target. No damage: recoil only moves the fort.
+    void apply_recoil(float x, float y, float radius,
+                      float dx, float dy, float strength);
+
     // Trace a laser beam from (ox,oy) along (dx,dy) up to `range`: damage +
     // optionally ignite EVERY strut it crosses, passing through beam-transparent
     // materials (bg-brace, ropes) and STOPPING at the first blocking one (wood).
diff --git a/src/game/data.cpp b/src/game/data.cpp
index 654cac6..3d9f6c0 100644
--- a/src/game/data.cpp
+++ b/src/game/data.cpp
@@ -36,6 +36,9 @@ MaterialDef read_material(const sol::table& m) {
     d.blocks_beam        = m.get_or("blocks_beam", true);
     d.tension_only    = m.get_or("tension_only", false);
     d.half_width      = m.get_or("half_width", 0.15f);
+    // Defaults match the flat costs struts used before they became per-material.
+    d.cost_metal      = m.get_or("cost_metal", 5.0f);
+    d.cost_energy     = m.get_or("cost_energy", 25.0f);
     d.texture         = m.get_or("texture", std::string(""));
     d.texture_forts   = m.get_or("texture_forts", std::string(""));
 
@@ -137,6 +140,7 @@ WeaponDef read_weapon(const sol::table& w) {
     d.beam_dps           = w.get_or("beam_dps", 120.0f);
     d.beam_duration      = w.get_or("beam_duration", 1.5f);
     d.energy_cost        = w.get_or("energy_cost", 0.0f);
+    d.recoil             = w.get_or("recoil", 0.0f);
     d.texture            = w.get_or("texture", std::string(""));
     d.projectile_texture = w.get_or("projectile_texture", std::string(""));
     d.texture_forts            = w.get_or("texture_forts", std::string(""));
diff --git a/src/game/data.hpp b/src/game/data.hpp
index fdf9e08..9b9aec1 100644
--- a/src/game/data.hpp
+++ b/src/game/data.hpp
@@ -24,6 +24,8 @@ struct WeaponDef {
     float beam_dps;            // HP damage per second to the struck strut
     float beam_duration;       // seconds the beam stays on
     float energy_cost;         // energy spent per shot (Forts EnergyFireCost)
+    float recoil;              // velocity kick shoved back into the FIRING
+                               // structure on each shot (Forts Recoil); 0 = none
     std::string texture;             // turret/base sprite (CC0 placeholder)
     std::string projectile_texture;  // shell sprite (CC0 placeholder)
     std::string texture_forts;            // preferred BYO Forts turret art