drm/output: Add constructors for DrmOutputRenderElements

src/backend/drm/output.rs

@@ -840,19 +840,41 @@ where
     _renderer: PhantomData<R>,
 }
 
-impl<R, E> Default for DrmOutputRenderElements<R, E>
+impl<R, E> DrmOutputRenderElements<R, E>
 where
     E: RenderElement<R>,
     R: Renderer + Bind<Dmabuf>,
     <R as Renderer>::TextureId: Texture + 'static,
     <R as Renderer>::Error: Send + Sync + 'static,
 {
-    fn default() -> Self {
+    /// Construct a new empty set of render elements
+    pub fn new() -> Self {
         DrmOutputRenderElements {
             render_elements: HashMap::new(),
             _renderer: PhantomData,
         }
     }
+
+    /// Construct a new empty set of render elements with pre-allocated capacity
+    /// for a number of crtcs.
+    pub fn with_capacity(cap: usize) -> Self {
+        DrmOutputRenderElements {
+            render_elements: HashMap::with_capacity(cap),
+            _renderer: PhantomData,
+        }
+    }
+}
+
+impl<R, E> Default for DrmOutputRenderElements<R, E>
+where
+    E: RenderElement<R>,
+    R: Renderer + Bind<Dmabuf>,
+    <R as Renderer>::TextureId: Texture + 'static,
+    <R as Renderer>::Error: Send + Sync + 'static,
+{
+    fn default() -> Self {
+        Self::new()
+    }
 }
 
 impl<R, E> DrmOutputRenderElements<R, E>