From 0e0574a0b448a28235ec056f2397c4568f5c9338 Mon Sep 17 00:00:00 2001
From: Daniel van Vugt <daniel.van.vugt@canonical.com>
Date: Fri, 23 Nov 2018 16:43:34 +0800
Subject: [PATCH] iconGrid: Eliminate JavaScript for painting/picking

The only reason for `vfunc_paint` and `vfunc_pick` existing was to
implement a culling optimization. Although that optimization actually
made performance worse than none at all because it forced the painting
and picking cycles to spend more time calling into JavaScript.

Turns out we don't have to choose between native code and culling though.
Just reimplement the culling using native ClutterActor functions and we
get the benefits of both.

Performance on an i7-7700:

Moving the cursor over the icon grid:
Before: 70% CPU, 5.5ms per frame
After : 60% CPU, 4.5ms per frame

Scrolling the icon grid:
Before: 60% CPU, 4.4ms per frame
After : 50% CPU, 3.3ms per frame

Helps with https://gitlab.gnome.org/GNOME/gnome-shell/issues/174
---
 js/ui/iconGrid.js | 29 ++++-------------------------
 1 file changed, 4 insertions(+), 25 deletions(-)

diff --git a/js/ui/iconGrid.js b/js/ui/iconGrid.js
index 94387a333..82b335cc5 100644
--- a/js/ui/iconGrid.js
+++ b/js/ui/iconGrid.js
@@ -344,10 +344,10 @@ var IconGrid = new Lang.Class({
 
             if (this._rowLimit && rowIndex >= this._rowLimit ||
                 this._fillParent && childBox.y2 > availHeight - this.bottomPadding) {
-                children[i]._skipPaint = true;
+                children[i].hide();
             } else {
                 children[i].allocate(childBox, flags);
-                children[i]._skipPaint = false;
+                children[i].show();
             }
 
             columnIndex++;
@@ -365,24 +365,6 @@ var IconGrid = new Lang.Class({
         }
     },
 
-    vfunc_paint() {
-        this.paint_background();
-
-        this.get_children().forEach(c => {
-            if (!c._skipPaint)
-                c.paint();
-        });
-    },
-
-    vfunc_pick(color) {
-        this.parent(color);
-
-        this.get_children().forEach(c => {
-            if (!c._skipPaint)
-                c.paint();
-        });
-    },
-
     vfunc_get_paint_volume(paintVolume) {
         // Setting the paint volume does not make sense when we don't have
         // any allocation
@@ -412,9 +394,6 @@ var IconGrid = new Lang.Class({
             if (!child.visible)
                 continue;
 
-            if (child._skipPaint)
-                continue;
-
             let childVolume = child.get_transformed_paint_volume(this);
             if (!childVolume)
                 return false
@@ -714,7 +693,7 @@ var IconGrid = new Lang.Class({
     },
 
     visibleItemsCount() {
-        return this.get_children().filter(c => !c._skipPaint).length;
+        return this.get_children().filter(c => c.is_visible()).length;
     },
 
     setSpacing(spacing) {
@@ -859,7 +838,7 @@ var PaginatedIconGrid = new Lang.Class({
         for (let i = 0; i < children.length; i++) {
             let childBox = this._calculateChildBox(children[i], x, y, box);
             children[i].allocate(childBox, flags);
-            children[i]._skipPaint = false;
+            children[i].show();
 
             columnIndex++;
             if (columnIndex == nColumns) {