examples/lua-scripting/scripts/test.lua

@@ -79,13 +79,12 @@ end ]]
 function on_update()
     -- Although WorldTransform isn't used, I only want to
     -- modify entities with that component.
-    local view = View.new(Transform, WorldTransform, Res(DeltaTime))
+    local view = View.new(Transform, Has(WorldTransform), Res(DeltaTime))
     local res = world:view_query(view)
 
     ---@param transform Transform
-    ---@param _wt WorldTransform
     ---@param dt DeltaTime
-    for entity, transform, _wt, dt in res:iter() do
+    for entity, transform, dt in res:iter() do
         transform:translate(0, 0.15 * dt, 0)
         entity:update(transform)
     end

lyra-scripting/scripts/lua/ecs.lua

@@ -1,13 +1,27 @@
----Create a Resource Query
+---Create a Resource query that will return the specific ECS world resource.
+---
+---@see ResQuery
 ---@param resource table|userdata
 ---@return ResQuery
 function Res(resource)
     return ResQuery.new(resource)
 end
 
----Create a `ChangedQuery` of a resource or component.
+---Create a `ChangedQuery` query that will return only if the resource or component has changed
+---since last tick.
+---
+---@see ChangedQuery
 ---@param val table|userdata
 ---@return ChangedQuery
 function Changed(val)
     return ChangedQuery.new(val)
+end
+
+---Create a `HasQuery` filter that will return only if the entity has a specific component.
+---
+---@see HasQuery
+---@param val table|userdata
+---@return HasQuery
+function Has(val)
+    return HasQuery.new(val)
 end

lyra-scripting/src/lib.rs

@@ -38,6 +38,7 @@ impl ReflectBranch {
     /// 
     /// # Panics
     /// If `self` is not a variant of [`ReflectBranch::Component`].
+    #[deprecated(note = "use ReflectBranch::as_component instead")]
     pub fn as_component_unchecked(&self) -> &ReflectedComponent {
         match self {
             ReflectBranch::Component(c) => c,
@@ -45,6 +46,16 @@ impl ReflectBranch {
         }
     }
 
+    /// Gets self as a [`ReflectedComponent`]. 
+    /// 
+    /// Returns `None` if `self` is not a component.
+    pub fn as_component(&self) -> Option<&ReflectedComponent> {
+        match self {
+            ReflectBranch::Component(c) => Some(c),
+            _ => None,
+        }
+    }
+
     /// Returns a boolean indicating if `self` is a reflection of a Component.
     pub fn is_component(&self) -> bool {
         matches!(self, ReflectBranch::Component(_))

lyra-scripting/src/lua/ecs/query/changed.rs

@@ -42,7 +42,10 @@ impl mlua::UserData for LuaChangedQuery {
                         }
 
                         // get the pointer of the component in the archetype column.
-                        let arch = world.entity_archetype(*en).unwrap();
+                        let arch = match world.entity_archetype(*en) {
+                            Some(a) => a,
+                            None => return Ok(mlua::Value::Boolean(false))
+                        };
                         let arch_idx = *arch.entity_indexes().get(&en).unwrap();
 
                         let col = match arch.get_column(tyid) {

lyra-scripting/src/lua/ecs/query/has.rs

@@ -0,0 +1,54 @@
+use crate::{
+    lua::{LuaComponent, FN_NAME_INTERNAL_ECS_QUERY_RESULT},
+    ScriptEntity, ScriptWorldPtr,
+};
+
+#[derive(Clone)]
+pub struct LuaHasQuery(LuaComponent);
+
+impl mlua::FromLua for LuaHasQuery {
+    fn from_lua(value: mlua::Value, _: &mlua::Lua) -> mlua::Result<Self> {
+        let tyname = value.type_name();
+        value
+            .as_userdata()
+            .ok_or(mlua::Error::FromLuaConversionError {
+                from: tyname,
+                to: "HasQuery".into(),
+                message: None,
+            })
+            .and_then(|ud| ud.borrow::<Self>())
+            .map(|ud| ud.clone())
+    }
+}
+
+impl mlua::UserData for LuaHasQuery {
+    fn add_methods<M: mlua::UserDataMethods<Self>>(methods: &mut M) {
+        methods.add_function("new", |_, comp: LuaComponent| {
+            let reflect = comp.reflect_type()?;
+            if !reflect.reflect_branch.is_component() {
+                Err(mlua::Error::runtime("provided type is not a component!"))
+            } else {
+                Ok(Self(comp))
+            }
+        });
+
+        methods.add_method(
+            FN_NAME_INTERNAL_ECS_QUERY_RESULT,
+            |_, this, (world, en): (ScriptWorldPtr, ScriptEntity)| {
+                let world = world.write();
+                let reflect = this.0.reflect_type()?;
+
+                let tyid = reflect.reflect_branch.reflect_type_id();
+
+                // try to find the entity's archetype and the component column in the archetype
+                let arch = match world.entity_archetype(*en) {
+                    Some(a) => a,
+                    None => return Ok(false),
+                };
+                let component_col = arch.get_column(tyid);
+
+                Ok(component_col.is_some())
+            },
+        );
+    }
+}

lyra-scripting/src/lua/ecs/query/mod.rs

@@ -4,6 +4,9 @@ pub use res::*;
 mod changed;
 pub use changed::*;
 
+mod has;
+pub use has::*;
+
 use lyra_ecs::Entity;
 
 use crate::{lua::{LuaComponent, FN_NAME_INTERNAL_ECS_QUERY_RESULT}, ScriptEntity, ScriptWorldPtr};

lyra-scripting/src/lua/ecs/view.rs

@@ -158,7 +158,8 @@ impl ViewResult {
                     let reflect = ud
                         .call_function::<ScriptBorrow>(FN_NAME_INTERNAL_REFLECT_TYPE, ())
                         .expect("Type does not implement 'reflect_type' properly");
-                    let refl_comp = reflect.reflect_branch.as_component_unchecked();
+                    let refl_comp = reflect.reflect_branch.as_component()
+                        .expect("`self` is not an instance of `ReflectBranch::Component`");
 
                     let dyn_type = QueryDynamicType::from_info(refl_comp.info);
                     view.push(dyn_type);
@@ -211,18 +212,25 @@ impl ViewResult {
     fn get_query_results(&self, entity: Entity) -> mlua::Result<QueryResult> {
         let mut query_vals = vec![];
 
+        // A modifier is used that will be incremented every time a filter allowed the query.
+        // this is used to remove the value of a filter without leaving a gap in the results.
+        let mut index_mod = 0;
         for (query, i) in &self.queries {
             let qres = query.get_query_result(self.world.clone(), entity)?;
             if let Some(val) = qres.as_boolean() {
-                // do not push a boolean to values, its considered a filter
                 if !val {
                     return Ok(QueryResult::None);
                 }
+                
+                index_mod += 1;
+                // do not push a boolean to values, its considered a filter
+                continue;
             } else if qres.is_nil() {
                 return Ok(QueryResult::AlwaysNone);
             }
 
-            query_vals.push((qres, *i));
+            let idx = (*i - index_mod).max(0);
+            query_vals.push((qres, idx));
         }
 
         Ok(QueryResult::Some(query_vals))

lyra-scripting/src/lua/providers/ecs.rs

@@ -1,7 +1,7 @@
 use lyra_ecs::ResourceObject;
 use lyra_reflect::Reflect;
 
-use crate::{lua::{ecs::{query::{LuaChangedQuery, LuaResQuery}, View}, wrappers::*, LuaContext, LuaWrapper, RegisterLuaType, FN_NAME_INTERNAL_REFLECT, FN_NAME_INTERNAL_REFLECT_TYPE}, ScriptApiProvider, ScriptBorrow, ScriptData, ScriptDynamicBundle, ScriptWorldPtr};
+use crate::{lua::{ecs::{query::{LuaChangedQuery, LuaHasQuery, LuaResQuery}, View}, wrappers::*, LuaContext, LuaWrapper, RegisterLuaType, FN_NAME_INTERNAL_REFLECT, FN_NAME_INTERNAL_REFLECT_TYPE}, ScriptApiProvider, ScriptBorrow, ScriptData, ScriptDynamicBundle, ScriptWorldPtr};
 
 //fn register_lua_proxy::<T: 
 
@@ -47,6 +47,7 @@ impl ScriptApiProvider for LyraEcsApiProvider {
         globals.set("View", ctx.create_proxy::<View>()?)?;
         globals.set("ResQuery", ctx.create_proxy::<LuaResQuery>()?)?;
         globals.set("ChangedQuery", ctx.create_proxy::<LuaChangedQuery>()?)?;
+        globals.set("HasQuery", ctx.create_proxy::<LuaHasQuery>()?)?;
 
         expose_comp_table_wrapper::<LuaCamera>(&ctx, &globals, "Camera")?;
         expose_comp_table_wrapper::<LuaFreeFlyCamera>(&ctx, &globals, "FreeFlyCamera")?;