From 1881f2174af6b00a47b88e830ca213486e558f5c Mon Sep 17 00:00:00 2001
From: Willow Sparks <willow.sparks@stfc.ac.uk>
Date: Thu, 5 Feb 2026 14:07:47 +0000
Subject: [PATCH] Fix physics.gravity() to read from PhysicsConfig

Previously returned hardcoded -20, now reads from lua.app_data<PhysicsConfig>()
if set, with fallback to default. Adds 2 tests for configured and default cases.
---
 crates/rust4d_scripting/Cargo.toml            |  1 +
 .../rust4d_scripting/src/bindings/physics.rs  | 92 +++++++++++++++----
 2 files changed, 75 insertions(+), 18 deletions(-)

diff --git a/crates/rust4d_scripting/Cargo.toml b/crates/rust4d_scripting/Cargo.toml
index 9df3e22..3381f2c 100644
--- a/crates/rust4d_scripting/Cargo.toml
+++ b/crates/rust4d_scripting/Cargo.toml
@@ -8,6 +8,7 @@ mlua = { version = "0.10", features = ["lua54", "vendored", "send"] }
 log = "0.4"
 rust4d_core = { path = "../rust4d_core" }
 rust4d_math = { path = "../rust4d_math" }
+rust4d_physics = { path = "../rust4d_physics" }
 notify = { version = "7.0", optional = true }
 
 [features]
diff --git a/crates/rust4d_scripting/src/bindings/physics.rs b/crates/rust4d_scripting/src/bindings/physics.rs
index eb0972a..7dad896 100644
--- a/crates/rust4d_scripting/src/bindings/physics.rs
+++ b/crates/rust4d_scripting/src/bindings/physics.rs
@@ -51,6 +51,7 @@
 use std::sync::atomic::{AtomicBool, Ordering};
 
 use mlua::prelude::*;
+use rust4d_physics::PhysicsConfig;
 
 use super::math::LuaVec4;
 
@@ -379,28 +380,30 @@ pub fn register(lua: &Lua) -> LuaResult<()> {
 
     // physics.gravity() -> Vec4
     //
-    // Get the current gravity vector.
+    // Get the current gravity vector from PhysicsConfig.
     //
-    // # Stub Behavior (LOW-16)
-    //
-    // Returns hardcoded default gravity (0, -20, 0, 0), NOT the actual physics
-    // config value. When PhysicsWorld is properly connected, this will return
-    // the configured gravity from PhysicsConfig. The default of -20 on Y is
-    // stronger than Earth gravity (~9.8) for snappier game feel.
+    // Returns the configured gravity as a Vec4 (0, gravity_y, 0, 0).
+    // If PhysicsConfig is not set via app_data, returns the default (-20 on Y).
     physics_table.set(
         "gravity",
-        lua.create_function(|_, ()| {
-            if !PHYSICS_WARNED.swap(true, Ordering::Relaxed) {
-                log::warn!(
-                    "[physics] PhysicsWorld not connected - all physics queries will return \
-                     empty/stub results."
-                );
-            }
+        lua.create_function(|lua, ()| {
+            // Try to get PhysicsConfig from app_data
+            let gravity_y = if let Some(config) = lua.app_data_ref::<PhysicsConfig>() {
+                log::trace!("[physics] gravity() - returning configured value: {}", config.gravity);
+                config.gravity
+            } else {
+                // No config set - use default and warn once
+                if !PHYSICS_WARNED.swap(true, Ordering::Relaxed) {
+                    log::warn!(
+                        "[physics] PhysicsConfig not set via app_data - using default gravity. \
+                         Call lua.set_app_data(physics_config) to configure."
+                    );
+                }
+                log::trace!("[physics] gravity() - no config, using default: -20.0");
+                PhysicsConfig::default().gravity
+            };
 
-            log::trace!("[physics] gravity() called - returning hardcoded default (0, -20, 0, 0)");
-            // STUB: Return default gravity (not actual config value)
-            // Real implementation would get from PhysicsConfig
-            Ok(LuaVec4(rust4d_math::Vec4::new(0.0, -20.0, 0.0, 0.0)))
+            Ok(LuaVec4(rust4d_math::Vec4::new(0.0, gravity_y, 0.0, 0.0)))
         })?,
     )?;
 
@@ -598,4 +601,57 @@ mod tests {
         .exec()
         .expect("stub markers should be present on physics query results");
     }
+
+    #[test]
+    fn test_gravity_reads_from_config() {
+        let lua = Lua::new();
+
+        // Set up a custom PhysicsConfig with non-default gravity
+        let mut config = PhysicsConfig::default();
+        config.gravity = -9.81; // Earth gravity instead of default -20
+        lua.set_app_data(config);
+
+        // Register bindings
+        math::register(&lua).unwrap();
+        register(&lua).unwrap();
+
+        // Verify gravity reads from config
+        let y: f32 = lua
+            .load(
+                r#"
+            local g = physics.gravity()
+            return g.y
+        "#,
+            )
+            .eval()
+            .expect("gravity should work");
+
+        assert!(
+            (y - (-9.81)).abs() < 0.001,
+            "gravity should read from PhysicsConfig (expected -9.81, got {})",
+            y
+        );
+    }
+
+    #[test]
+    fn test_gravity_default_without_config() {
+        let lua = create_lua_with_physics();
+        // No PhysicsConfig set - should use default
+
+        let y: f32 = lua
+            .load(
+                r#"
+            local g = physics.gravity()
+            return g.y
+        "#,
+            )
+            .eval()
+            .expect("gravity should work");
+
+        assert!(
+            (y - (-20.0)).abs() < 0.001,
+            "gravity should use default when no config set (expected -20.0, got {})",
+            y
+        );
+    }
 }
-- 
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