Debug FPS display with rendering backend info

www/dc_plugin.js

@@ -261,5 +261,49 @@
         window.addEventListener(ev, startAudio, true);
     });
 
+    function gfxInfo() {
+        try {
+            var canvas = document.getElementById("glcanvas");
+            if (!canvas) {
+                var cs = document.getElementsByTagName("canvas");
+                canvas = cs.length ? cs[0] : null;
+            }
+            if (!canvas) return "";
+            var gl = canvas.getContext("webgl2");
+            var version = "WebGL 2";
+            if (!gl) {
+                gl = canvas.getContext("webgl");
+                version = "WebGL 1";
+            }
+            if (!gl) return "";
+            var versionName = gl.getParameter(gl.VERSION) || version;
+            var dbg = gl.getExtension("WEBGL_debug_renderer_info");
+            var gpu = dbg ? gl.getParameter(dbg.UNMASKED_RENDERER_WEBGL) || "" : "";
+            var vendor = dbg ? gl.getParameter(dbg.UNMASKED_VENDOR_WEBGL) || "" : "";
+            var api = "WebGL";
+            var all = versionName + " " + gpu + " " + vendor;
+            if (all.indexOf("Vulkan") >= 0) api = "Vulkan";
+            else if (all.indexOf("Metal") >= 0) api = "Metal";
+            else if (all.indexOf("Direct3D") >= 0 || all.indexOf("D3D") >= 0) api = "D3D";
+            else if (all.indexOf("OpenGL") >= 0) api = "OpenGL";
+            return versionName + " | " + api + " | " + (gpu || vendor || api);
+        } catch (e) {
+            return "";
+        }
+    }
+
+    function registerGfx(importObject) {
+        importObject.env.dc_renderer = function () {
+            pending = new TextEncoder().encode(gfxInfo());
+            return pending.length;
+        };
+    }
+
+    var oldRegister = register;
+    register = function (importObject) {
+        oldRegister(importObject);
+        registerGfx(importObject);
+    };
+
     miniquad_add_plugin({ register_plugin: register, version: 1, name: "dungeoncraft" });
 })();