[gnome-shell] iconGrid: Eliminate JavaScript for painting/picking

[Florian Müllner <fmuellner src gnome org>]

commit 0e0574a0b448a28235ec056f2397c4568f5c9338
Author: Daniel van Vugt <daniel van vugt canonical com>
Date:   Fri Nov 23 16:43:34 2018 +0800

    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) {