m: Cache document in web frontend (#66)

src/web.rs

@@ -7,14 +7,16 @@ use web_sys::ImageData;
 
 use crate::SoftBufferError;
 
-pub struct WebImpl {
-    canvas: HtmlCanvasElement,
-    ctx: CanvasRenderingContext2d,
+/// Display implementation for the web platform.
+///
+/// This just caches the document to prevent having to query it every time.
+pub struct WebDisplayImpl {
+    document: web_sys::Document,
 }
 
-impl WebImpl {
-    pub fn new(handle: WebWindowHandle) -> Result<Self, SoftBufferError> {
-        let canvas: HtmlCanvasElement = web_sys::window()
+impl WebDisplayImpl {
+    pub(super) fn new() -> Result<Self, SoftBufferError> {
+        let document = web_sys::window()
             .ok_or_else(|| {
                 SoftBufferError::PlatformError(
                     Some("`window` is not present in this runtime".into()),
@@ -27,7 +29,21 @@ impl WebImpl {
                     Some("`document` is not present in this runtime".into()),
                     None,
                 )
-            })?
+            })?;
+
+        Ok(Self { document })
+    }
+}
+
+pub struct WebImpl {
+    canvas: HtmlCanvasElement,
+    ctx: CanvasRenderingContext2d,
+}
+
+impl WebImpl {
+    pub fn new(display: &WebDisplayImpl, handle: WebWindowHandle) -> Result<Self, SoftBufferError> {
+        let canvas: HtmlCanvasElement = display
+            .document
             .query_selector(&format!("canvas[data-raw-handle=\"{}\"]", handle.id))
             // `querySelector` only throws an error if the selector is invalid.
             .unwrap()