3 files changed, 133 insertions, 0 deletions
diff --git a/engine/Cargo.toml b/engine/Cargo.toml
index 322e6c3..f46433e 100644
--- a/engine/Cargo.toml
+++ b/engine/Cargo.toml
@@ -48,6 +48,10 @@ branch = "prebuilt-and-artifacts"
 version = "=0.16.0-alpha.1"
 features = ["freetype"]
 
+[dependencies.dear-imguizmo]
+version = "=0.16.0-alpha.1"
+default-features = false # A dependency on glam is not desired
+
 [build-dependencies]
 build-rs = "0.3.4"
 serde = { version = "1.0.228", features = ["derive"] }
diff --git a/engine/src/ui/view.rs b/engine/src/ui/view.rs
index ed714d6..42601a3 100644
--- a/engine/src/ui/view.rs
+++ b/engine/src/ui/view.rs
@@ -1 +1,2 @@
+pub mod transform_3d;
 pub mod world;
diff --git a/engine/src/ui/view/transform_3d.rs b/engine/src/ui/view/transform_3d.rs
new file mode 100644
index 0000000..a426b2a
--- /dev/null
+++ b/engine/src/ui/view/transform_3d.rs
@@ -0,0 +1,128 @@
+use dear_imguizmo::GuizmoExt;
+
+use crate::camera::{Active as ActiveCamera, Camera};
+use crate::data_types::dimens::Dimens3;
+use crate::ecs::pair::ChildOf;
+use crate::ecs::query::term::{Traverse, TraverseUp, With, Without};
+use crate::ecs::sole::Single;
+use crate::ecs::Query;
+use crate::projection::ClipVolume as ProjectionClipVolume;
+use crate::scene::{Active as ActiveScene, Scene};
+use crate::transform::Transform;
+use crate::ui::dear_imgui::{
+    Context as DearImguiContext,
+    TargetWindow as DearImguiTargetWindow,
+};
+use crate::vector::Vec3;
+use crate::windowing::window::{Closed as WindowClosed, Window};
+
+pub fn show(
+    subject_query: Query<(
+        &mut Transform,
+        Traverse<(With<Scene>, With<ActiveScene>), TraverseUp, ChildOf>,
+        Without<ActiveCamera>,
+    )>,
+    camera_query: Query<(
+        &Camera,
+        &Transform,
+        Traverse<(With<Scene>, With<ActiveScene>), TraverseUp, ChildOf>,
+        With<ActiveCamera>,
+    )>,
+    target_window_query: Query<(
+        &Window,
+        With<DearImguiTargetWindow>,
+        Without<WindowClosed>,
+    )>,
+    mut dear_imgui_context: Single<DearImguiContext>,
+) -> Result<(), crate::Error>
+{
+    let dear_imgui_context = dear_imgui_context.get_mut()?;
+
+    let Some(frame) = dear_imgui_context.frame() else {
+        return Ok(());
+    };
+
+    let Some((camera, camera_world_pos)) = camera_query.iter().next() else {
+        return Ok(());
+    };
+
+    let Some((target_window,)) = target_window_query.iter().next() else {
+        return Ok(());
+    };
+
+    let gizmo = frame.guizmo();
+
+    let [display_width, display_height] = frame.io().display_size();
+
+    gizmo.set_rect(0.0, 0.0, display_width, display_height);
+
+    // The widgets should appear under dear imgui windows
+    gizmo.set_drawlist_background();
+
+    let col_major_view = flatten_matrix(
+        camera
+            .to_view_matrix(camera_world_pos.position)
+            .to_column_major(),
+    );
+
+    let col_major_projection = flatten_matrix(
+        camera
+            .projection
+            .to_matrix_rh(target_window.inner_size, ProjectionClipVolume::NegOneToOne)
+            .to_column_major(),
+    );
+
+    for (subject_index, (mut subject_transform,)) in subject_query.iter().enumerate() {
+        let subject_index = match i32::try_from(subject_index) {
+            Ok(subject_index) => subject_index,
+            Err(err) => {
+                tracing::error!("Invalid subject index {subject_index}: {err}");
+                break;
+            }
+        };
+
+        // No rotation
+        let rotation = [0.0, 0.0, 0.0];
+
+        let mut col_major_model_mat = dear_imguizmo::recompose_matrix(
+            &subject_transform.position.into(),
+            &rotation,
+            &subject_transform.scale.into(),
+        );
+
+        let _id_token = gizmo.push_id(subject_index);
+
+        let used = gizmo
+            .manipulate_config(
+                &col_major_view,
+                &col_major_projection,
+                &mut col_major_model_mat,
+            )
+            .operation(
+                dear_imguizmo::Operation::TRANSLATE | dear_imguizmo::Operation::SCALE,
+            )
+            .mode(dear_imguizmo::Mode::World)
+            .build();
+
+        if used {
+            let (translation, _rotation, scale) =
+                dear_imguizmo::decompose_matrix(&col_major_model_mat);
+
+            subject_transform.position = Vec3::from(translation);
+            subject_transform.scale = Dimens3::from(scale);
+        }
+    }
+
+    Ok(())
+}
+
+fn flatten_matrix(mat: [[f32; 4]; 4]) -> [f32; 4 * 4]
+{
+    let flattened = mat.as_flattened();
+
+    let Some(flattened) = flattened.as_array::<{ 4 * 4 }>() else {
+        unreachable!();
+    };
+
+    flattened.clone()
+}