egui_web glow painter: return errors instead of panic

egui_web/src/backend.rs

@@ -8,9 +8,9 @@ pub use egui::{pos2, Color32};
 fn create_painter(canvas_id: &str) -> Result<Box<dyn Painter>, JsValue> {
     // Glow takes precedence:
     #[cfg(all(feature = "glow"))]
-    return Ok(Box::new(crate::glow_wrapping::WrappedGlowPainter::new(
+    return Ok(Box::new(
-        canvas_id,
+        crate::glow_wrapping::WrappedGlowPainter::new(canvas_id).map_err(JsValue::from)?,
-    )));
+    ));
 
     #[cfg(all(feature = "webgl", not(feature = "glow")))]
     if let Ok(webgl2_painter) = webgl2::WebGl2Painter::new(canvas_id) {

egui_web/src/glow_wrapping.rs

@@ -1,4 +1,3 @@
-use crate::{canvas_element_or_die, console_error};
 use egui::{ClippedMesh, Rgba};
 use egui_glow::glow;
 use wasm_bindgen::JsCast;
@@ -15,27 +14,21 @@ pub(crate) struct WrappedGlowPainter {
 }
 
 impl WrappedGlowPainter {
-    pub fn new(canvas_id: &str) -> Self {
+    pub fn new(canvas_id: &str) -> Result<Self, String> {
-        let canvas = canvas_element_or_die(canvas_id);
+        let canvas = crate::canvas_element_or_die(canvas_id);
 
-        let (glow_ctx, shader_prefix) = init_glow_context_from_canvas(&canvas);
+        let (glow_ctx, shader_prefix) = init_glow_context_from_canvas(&canvas)?;
 
         let dimension = [canvas.width() as i32, canvas.height() as i32];
         let painter = egui_glow::Painter::new(&glow_ctx, Some(dimension), shader_prefix)
-            .map_err(|error| {
+            .map_err(|error| format!("Error starting glow painter: {}", error))?;
-                console_error(format!(
-                    "some error occurred in initializing glow painter\n {}",
-                    error
-                ))
-            })
-            .unwrap();
 
-        Self {
+        Ok(Self {
             glow_ctx,
             canvas,
             canvas_id: canvas_id.to_owned(),
             painter,
-        }
+        })
     }
 }
 
@@ -90,7 +83,9 @@ impl crate::Painter for WrappedGlowPainter {
 }
 
 /// Returns glow context and shader prefix.
-fn init_glow_context_from_canvas(canvas: &HtmlCanvasElement) -> (glow::Context, &'static str) {
+fn init_glow_context_from_canvas(
+    canvas: &HtmlCanvasElement,
+) -> Result<(glow::Context, &'static str), String> {
     const BEST_FIRST: bool = true;
 
     let result = if BEST_FIRST {
@@ -103,9 +98,9 @@ fn init_glow_context_from_canvas(canvas: &HtmlCanvasElement) -> (glow::Context,
     };
 
     if let Some(result) = result {
-        result
+        Ok(result)
     } else {
-        panic!("WebGL isn't supported");
+        Err("WebGL isn't supported".into())
     }
 }
 

egui_web/src/webgl1.rs

@@ -35,7 +35,7 @@ impl WebGlPainter {
 
         let gl = canvas
             .get_context("webgl")?
-            .ok_or_else(|| JsValue::from("Failed to get WebGl context"))?
+            .ok_or_else(|| JsValue::from("Failed to get WebGL context"))?
             .dyn_into::<WebGlRenderingContext>()?;
 
         // --------------------------------------------------------------------