GPU accelerated rendering & Mouse-handler optimization (#146)

* summarize edges setting under performance section & default on

* comment-out isBlank function that prevents GPU acceleration

* reduced ctx calls for summary and plus symbols

* removed old commit relics, ctx.ellipse comment

* added arrow LOD check for deferred edges

* moushandler more efficient hover computation

* replaced drawEllipse call, canvas ctx settings comments

* summarize edges default off, comments

src/renderer/canvas_manager.ts

@@ -222,6 +222,9 @@ export class CanvasManager {
         this.indices = [];
     }
 
+    // TODO: WARNING! This function uses ctx.getImageData() which forces
+    // the browser to turn off GPU accelerated canvas painting!
+    // It needs to be reworked to not use getImageData() anymore.
     public isBlank(): boolean {
         const ctx = this.canvas.getContext('2d');
         if (!ctx)
@@ -247,11 +250,13 @@ export class CanvasManager {
             return;
         this.contention++;
         this.request_scale = true;
-        if (this.isBlank()) {
-            this.renderer.set_bgcolor('black');
-            this.renderer.zoom_to_view(null, false);
-            diff = 0.01;
-        }
+
+        // Don't use the easteregg feature as long as isBlank() is not fixed!
+        // if (this.isBlank()) {
+        //     this.renderer.set_bgcolor('black');
+        //     this.renderer.zoom_to_view(null, false);
+        //     diff = 0.01;
+        // }
 
         this.scale_origin.x = x;
         this.scale_origin.y = y;