Added WebGlContextOption for eframe::WebOptions (#1803)

* Added WebGlContextOption for eframe::WebOptions

* Fix doclink

* Fix minor doc issue

Co-authored-by: xxvvii <xuwei@aecg.com.cn>
Co-authored-by: Emil Ernerfeldt <emil.ernerfeldt@gmail.com>

eframe/src/epi.rs

@@ -330,6 +330,11 @@ pub struct WebOptions {
     ///
     /// Default: `Theme::Dark`.
     pub default_theme: Theme,
+
+    /// Which version of WebGl context to select
+    ///
+    /// Default: [`WebGlContextOption::BestFirst`].
+    pub webgl_context_option: WebGlContextOption,
 }
 
 #[cfg(target_arch = "wasm32")]
@@ -338,6 +343,7 @@ impl Default for WebOptions {
         Self {
             follow_system_theme: true,
             default_theme: Theme::Dark,
+            webgl_context_option: WebGlContextOption::BestFirst,
         }
     }
 }
@@ -368,6 +374,22 @@ impl Theme {
 
 // ----------------------------------------------------------------------------
 
+/// WebGl Context options
+#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+pub enum WebGlContextOption {
+    /// Force Use WebGL1.
+    WebGl1,
+    /// Force use WebGL2.
+    WebGl2,
+    /// Use WebGl2 first.
+    BestFirst,
+    /// Use WebGl1 first
+    CompatibilityFirst,
+}
+
+// ----------------------------------------------------------------------------
+
 /// What rendering backend to use.
 ///
 /// You need to enable the "glow" and "wgpu" features to have a choice.

eframe/src/web/backend.rs

@@ -160,7 +160,8 @@ impl AppRunner {
         web_options: crate::WebOptions,
         app_creator: epi::AppCreator,
     ) -> Result<Self, JsValue> {
-        let painter = WrappedGlowPainter::new(canvas_id).map_err(JsValue::from)?; // fail early
+        let painter = WrappedGlowPainter::new(canvas_id, web_options.webgl_context_option)
+            .map_err(JsValue::from)?; // fail early
 
         let system_theme = if web_options.follow_system_theme {
             super::system_theme()

eframe/src/web/glow_wrapping.rs

@@ -1,3 +1,4 @@
+use crate::WebGlContextOption;
 use egui::{ClippedPrimitive, Rgba};
 use egui_glow::glow;
 use wasm_bindgen::JsCast;
@@ -13,10 +14,10 @@ pub(crate) struct WrappedGlowPainter {
 }
 
 impl WrappedGlowPainter {
-    pub fn new(canvas_id: &str) -> Result<Self, String> {
+    pub fn new(canvas_id: &str, options: WebGlContextOption) -> Result<Self, String> {
         let canvas = super::canvas_element_or_die(canvas_id);
 
-        let (gl, shader_prefix) = init_glow_context_from_canvas(&canvas)?;
+        let (gl, shader_prefix) = init_glow_context_from_canvas(&canvas, options)?;
         let gl = std::sync::Arc::new(gl);
 
         let dimension = [canvas.width() as i32, canvas.height() as i32];
@@ -91,16 +92,19 @@ impl WrappedGlowPainter {
 /// Returns glow context and shader prefix.
 fn init_glow_context_from_canvas(
     canvas: &HtmlCanvasElement,
+    options: WebGlContextOption,
 ) -> Result<(glow::Context, &'static str), String> {
-    const BEST_FIRST: bool = true;
-
-    let result = if BEST_FIRST {
+    let result = match options {
+        // Force use WebGl1
+        WebGlContextOption::WebGl1 => init_webgl1(canvas),
+        // Force use WebGl2
+        WebGlContextOption::WebGl2 => init_webgl2(canvas),
         // Trying WebGl2 first
-        init_webgl2(canvas).or_else(|| init_webgl1(canvas))
-    } else {
+        WebGlContextOption::BestFirst => init_webgl2(canvas).or_else(|| init_webgl1(canvas)),
         // Trying WebGl1 first (useful for testing).
-        tracing::warn!("Looking for WebGL1 first");
-        init_webgl1(canvas).or_else(|| init_webgl2(canvas))
+        WebGlContextOption::CompatibilityFirst => {
+            init_webgl1(canvas).or_else(|| init_webgl2(canvas))
+        }
     };
 
     if let Some(result) = result {