[pve-devel] [PATCH pve-xtermjs] xtermjs: try to detect hardware support for webgl2

[Dominik Csapak <d.csapak@proxmox.com>]

with the new webgl renderer, chrome/chromium has buggy software support for
emulating this (see [0]), so we have to detect that manually and prevent
loading the addon. This fixes the issue that on chrome without hw
support, it would not always render every character.

Firefox does not have support for a software renderer and the
loading/detection throws an exception, falling back to the default
renderer.

0: https://github.com/xtermjs/xterm.js/issues/4574

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
tested with and without webgl hardware support on firefox/chrome/chromium

 xterm.js/src/main.js | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/xterm.js/src/main.js b/xterm.js/src/main.js
index 85cc399..1575697 100644
--- a/xterm.js/src/main.js
+++ b/xterm.js/src/main.js
@@ -154,9 +154,15 @@ function createTerminal() {
     term = new Terminal(getTerminalSettings());
     term.open(terminalContainer);
     term.loadAddon(fitAddon);
+    let loadedWebgl = false;
     try {
-	term.loadAddon(webglAddon);
-    } catch (_e) {
+	if (detectWebgl()) {
+	    term.loadAddon(webglAddon);
+	    loadedWebgl = true;
+	}
+    } catch (_e) { }
+
+    if (!loadedWebgl) {
 	console.warn("webgl-addon loading failed, falling back to regular dom renderer");
     }
 
@@ -384,3 +390,15 @@ function errorTerminal(event) {
     term.dispose();
     updateState(states.disconnected, event.msg, event.code);
 }
+
+// try to detect hardware acceleration, can throw an exception if there is no webgl support
+//
+// for chrome we have to give the parameter, otherwise it'll use its software renderer
+// which is buggy: https://github.com/xtermjs/xterm.js/issues/4574
+//
+// firefox will fail on the getContext anyway if there is not hardware support
+function detectWebgl() {
+    const canvas = document.createElement("canvas");
+    const gl = canvas.getContext("webgl2", { failIfMajorPerformanceCaveat: true });
+    return !!gl;
+}
-- 
2.30.2