Fix build errors

piet-common/Cargo.toml

@@ -36,3 +36,6 @@ png = { version = "0.16.1", optional = true }
 
 [target.'cfg(target_arch="wasm32")'.dependencies]
 piet-web = { version = "0.0.12", path = "../piet-web" }
+web-sys = { version = "0.3.36", features = ["console", "Window", "CanvasGradient", "CanvasRenderingContext2d", "CanvasWindingRule", "Document", "Element", "HtmlCanvasElement", "ImageBitmap", "ImageData", "TextMetrics"] }
+wasm-bindgen = "0.2.59"
+

piet-common/src/web_back.rs

@@ -1,7 +1,14 @@
 //! Support for piet Web back-end.
 
+use piet::{ErrorKind, ImageFormat};
 #[doc(hidden)]
 pub use piet_web::*;
+
+use std::fmt;
+use std::marker::PhantomData;
+
+use wasm_bindgen::JsCast;
+
 pub type Piet<'a> = WebRenderContext<'a>;
 
 /// The associated brush type for this backend.
@@ -44,8 +51,8 @@ pub struct Device;
 
 /// A struct provides a `RenderContext` and then can have its bitmap extracted.
 pub struct BitmapTarget<'a> {
-    canvas: HtmlCanvasElement,
-    context: CanvasRenderingContext2d,
+    canvas: web_sys::HtmlCanvasElement,
+    context: web_sys::CanvasRenderingContext2d,
     phantom: PhantomData<&'a ()>,
 }
 
@@ -67,10 +74,11 @@ impl Device {
             .create_element("canvas")
             .unwrap()
             .dyn_into::<web_sys::HtmlCanvasElement>()
-            .unwrap()
+            .unwrap();
         let context = canvas
             .get_context("2d")
             .unwrap()
+            .unwrap()
             .dyn_into::<web_sys::CanvasRenderingContext2d>()
             .unwrap();
 
@@ -89,22 +97,46 @@ impl Device {
 impl<'a> BitmapTarget<'a> {
     /// Get a piet `RenderContext` for the bitmap.
     pub fn render_context(&mut self) -> WebRenderContext {
-        WebRenderContext::new(self.ctx.clone(), web_sys::window().unwrap())
+        WebRenderContext::new(self.context.clone(), web_sys::window().unwrap())
     }
 
     /// Get raw RGBA pixels from the bitmap.
-    pub fn into_raw_pixels(mut self, fmt: ImageFormat) -> Result<Vec<u8>, piet::Error> {
+    pub fn into_raw_pixels(self, fmt: ImageFormat) -> Result<Vec<u8>, piet::Error> {
         // TODO: This code is just a snippet. A thorough review and testing should be done before
         // this is used. It is here for compatibility with druid.
+
         if fmt != ImageFormat::RgbaPremul {
-            return Err(piet::new_eror(ErrorKind::NotSupported));
+            return Err(piet::new_error(ErrorKind::NotSupported));
         }
 
-        let mut raw_data = vec![0; width * height * 4];
-        let img_data = self.context.get_image_data()
-            .map_err(Into::<Box<dyn std::error::Error>>::into)?;
+        let width = self.canvas.width() as usize;
+        let height = self.canvas.height() as usize;
+
+        let img_data = self
+            .context
+            .get_image_data(0.0, 0.0, width as f64, height as f64)
+            .map_err(|jsv| piet::new_error(ErrorKind::BackendError(Box::new(JsError::new(jsv)))))?;
 
         // ImageDate is in RGBA order. This should be the same as expected on the output.
         Ok(img_data.data().0)
     }
 }
+
+#[derive(Clone, Debug)]
+struct JsError {
+    jsv: wasm_bindgen::JsValue,
+}
+
+impl JsError {
+    fn new(jsv: wasm_bindgen::JsValue) -> Self {
+        JsError { jsv }
+    }
+}
+
+impl fmt::Display for JsError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "{:?}", self.jsv)
+    }
+}
+
+impl std::error::Error for JsError {}