Expose Luau 3-vectors support

The Luau VM supports native f32 3-vectors so that typical
linear algebra operations are fast in game code.

TODO: Luau can also be built for native 4-vectors through a
compilation option.  This path should be supported also, as that's
most probably a better default for 3d-games.  3-vectors are fine
for 2d-games :)

src/zigluau/lib.zig

@@ -244,6 +244,14 @@ pub const Lua = struct {
         }
     }
 
+    fn vectorCtor(l: *Lua) i32 {
+        const x = l.toNumber(1) catch unreachable;
+        const y = l.toNumber(2) catch unreachable;
+        const z = l.toNumber(3) catch unreachable;
+        c.lua_pushvector(l.state, @floatCast(x), @floatCast(y), @floatCast(z));
+        return 1;
+    }
+
     /// Initialize a Lua state with the given allocator
     /// See https://www.lua.org/manual/5.1/manual.html#lua_newstate
     pub fn init(allocator: Allocator) !Lua {
@@ -255,10 +263,12 @@ pub const Lua = struct {
         allocator_ptr.* = allocator;
 
         const state = c.lua_newstate(alloc, allocator_ptr) orelse return error.Memory;
-        return Lua{
+        var lua = Lua{
             .allocator = allocator_ptr,
             .state = state,
         };
+        lua.register("vector", wrap(vectorCtor));
+        return lua;
     }
 
     /// Deinitialize a Lua state and free all memory
@@ -670,6 +680,12 @@ pub const Lua = struct {
         c.lua_pushvalue(lua.state, index);
     }
 
+    /// Pushes a floating point 3-vector (or 4-vector if configured) `v` onto the stack
+    /// See https://www.lua.org/manual/5.1/manual.html#lua_pushinteger
+    pub fn pushVector(lua: *Lua, v: @Vector(3, f32)) void {
+        c.lua_pushvector(lua.state, v[0], v[1], v[2]);
+    }
+
     /// Returns true if the two values in indices `index1` and `index2` are primitively equal
     /// Bypasses __eq metamethods
     /// Returns false if not equal, or if any index is invalid
@@ -879,6 +895,17 @@ pub const Lua = struct {
         return error.Fail;
     }
 
+    /// Converts the Lua value at the given `index` to a f32 3-vector
+    /// The Lua value must be an integer, or a number, or a string convertible to an integer otherwise toInteger returns 0
+    /// See https://www.lua.org/manual/5.1/manual.html#lua_tointeger
+    pub fn toVector(lua: *Lua, index: i32) !@Vector(3, f32) {
+        const res = c.lua_tovector(lua.state, index);
+        if (res) |r| {
+            return @Vector(3, f32){ r[0], r[1], r[2] };
+        }
+        return @Vector(3, f32){ 0, 0, 0 };
+    }
+
     /// Returns the `LuaType` of the value at the given index
     /// Note that this is equivalent to lua_type but because type is a Zig primitive it is renamed to `typeOf`
     /// See https://www.lua.org/manual/5.1/manual.html#lua_type
@@ -1136,7 +1163,15 @@ pub const Lua = struct {
     /// TODO: does it make sense to have this in Luau?
     pub fn loadString(lua: *Lua, str: [:0]const u8) !void {
         var size: usize = 0;
-        const bytecode = c.luau_compile(str.ptr, str.len, null, &size);
+        var opts = c.lua_CompileOptions{
+            .optimizationLevel = 1,
+            .debugLevel = 1,
+            .coverageLevel = 0,
+            .vectorLib = null,
+            .vectorCtor = "vector",
+            .mutableGlobals = null,
+        };
+        const bytecode = c.luau_compile(str.ptr, str.len, &opts, &size);
 
         // Failed to allocate memory for the out buffer
         if (bytecode == null) return error.Memory;

src/zigluau/tests.zig

@@ -1089,6 +1089,32 @@ test "objectLen" {
     try testing.expectEqual(@as(i32, 3), lua.objectLen(-1));
 }
 
+// Luau supports a 'vector' type that's either a 3-vector or 4-vector (if configured at build-time)
+test "luau vectors" {
+    var lua = try Lua.init(testing.allocator);
+    defer lua.deinit();
+    lua.openLibs();
+
+    try lua.doString(
+        \\function test()
+        \\  local a = vector(1, 2, 3)
+        \\  local b = vector(4, 5, 6)
+        \\  local c = (a + b) * vector(2, 2, 2)
+        \\  return c
+        \\end
+    );
+    _ = lua.getGlobal("test");
+    try lua.protectedCall(0, 1, 0);
+    var v = try lua.toVector(-1);
+    try testing.expectEqual(v[0], 10.0);
+    try testing.expectEqual(v[1], 14.0);
+    try testing.expectEqual(v[2], 18.0);
+
+    lua.pushVector(@Vector(3, f32){ 1, 2, 3 });
+    v = try lua.toVector(-1);
+    try testing.expectEqual(v, @Vector(3, f32){ 1, 2, 3 });
+}
+
 test {
     testing.refAllDecls(Lua);
     testing.refAllDecls(Buffer);