feat: add custom camera viewport support. (#100)

crates/bones_bevy_renderer/src/lib.rs

@@ -299,6 +299,13 @@ fn sync_cameras<W: HasBonesWorld>(
                 }
                 _ => (),
             }
+            camera.viewport = bones_camera
+                .viewport
+                .map(|x| bevy::render::camera::Viewport {
+                    physical_position: x.position,
+                    physical_size: x.size,
+                    depth: x.depth_min..x.depth_max,
+                });
 
             *transform = bones_transform.into_bevy();
         } else {

crates/bones_render/src/camera.rs

@@ -15,13 +15,35 @@ pub struct Camera {
     pub height: f32,
     /// Whether or not the camera is enabled and rendering.
     pub active: bool,
+    /// An optional viewport override, allowing you to specify that the camera should render to only
+    /// a portion of the window.
+    ///
+    /// This can be used, for example, for split screen functionality.
+    pub viewport: Option<Viewport>,
+}
+
+/// A custom viewport specification for a [`Camera`].
+#[derive(Clone, Copy, Debug)]
+#[repr(C)]
+pub struct Viewport {
+    /// The physical position to render this viewport to within the RenderTarget of this Camera.
+    /// (0,0) corresponds to the top-left corner.
+    pub position: UVec2,
+    /// The physical size of the viewport rectangle to render to within the RenderTarget of this
+    /// Camera. The origin of the rectangle is in the top-left corner.
+    pub size: UVec2,
+    /// The minimum depth to render (on a scale from 0.0 to 1.0).
+    pub depth_min: f32,
+    /// The maximum depth to render (on a scale from 0.0 to 1.0).
+    pub depth_max: f32,
 }
 
 impl Default for Camera {
     fn default() -> Self {
         Self {
             height: 400.0,
             active: true,
+            viewport: None,
         }
     }
 }