Implement custom window scroll

2 files changed, 109 insertions, 5 deletions

diff --git a/ext/mixed/js/display.js b/ext/mixed/js/display.js
index a3d618e5..e3c44507 100644
--- a/ext/mixed/js/display.js
+++ b/ext/mixed/js/display.js
@@ -31,6 +31,8 @@ class Display {
 
         this.dependencies = {};
 
+        this.windowScroll = new WindowScroll();
+
         document.addEventListener('keydown', this.onKeyDown.bind(this));
         document.addEventListener('wheel', this.onWheel.bind(this), {passive: false});
     }
@@ -53,11 +55,12 @@ class Display {
             e.preventDefault();
 
             const link = e.target;
+            this.windowScroll.toY(0);
             const context = {
                 source: {
                     definitions: this.definitions,
                     index: this.entryIndexFind(link),
-                    scroll: $('html,body').scrollTop()
+                    scroll: this.windowScroll.y
                 }
             };
 
@@ -102,11 +105,12 @@ class Display {
                 textSource.cleanup();
             }
 
+            this.windowScroll.toY(0);
             const context = {
                 source: {
                     definitions: this.definitions,
                     index: this.entryIndexFind(clickedElement),
-                    scroll: $('html,body').scrollTop()
+                    scroll: this.windowScroll.y
                 }
             };
 
@@ -410,7 +414,7 @@ class Display {
 
         $('.current').hide().eq(index).show();
 
-        const container = $('html,body').stop();
+        this.windowScroll.stop();
         const entry = $('.entry').eq(index);
         let target;
 
@@ -421,9 +425,9 @@ class Display {
         }
 
         if (smooth) {
-            container.animate({scrollTop: target}, 200);
+            this.windowScroll.animate(this.windowScroll.x, target, 200);
         } else {
-            container.scrollTop(target);
+            this.windowScroll.toY(target);
         }
 
         this.index = index;
diff --git a/ext/mixed/js/scroll.js b/ext/mixed/js/scroll.js
new file mode 100644
index 00000000..824fd92b
--- /dev/null
+++ b/ext/mixed/js/scroll.js
@@ -0,0 +1,100 @@
+/*
+ * Copyright (C) 2019  Alex Yatskov <alex@foosoft.net>
+ * Author: Alex Yatskov <alex@foosoft.net>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+
+class WindowScroll {
+    constructor() {
+        this.animationRequestId = null;
+        this.animationStartTime = 0;
+        this.animationStartX = 0;
+        this.animationStartY = 0;
+        this.animationEndTime = 0;
+        this.animationEndX = 0;
+        this.animationEndY = 0;
+        this.requestAnimationFrameCallback = (t) => this.onAnimationFrame(t);
+    }
+
+    toY(y) {
+        this.to(this.x, y);
+    }
+
+    toX(x) {
+        this.to(x, this.y);
+    }
+
+    to(x, y) {
+        this.stop();
+        window.scroll(x, y);
+    }
+
+    animate(x, y, time) {
+        this.animationStartX = this.x;
+        this.animationStartY = this.y;
+        this.animationStartTime = window.performance.now();
+        this.animationEndX = x;
+        this.animationEndY = y;
+        this.animationEndTime = this.animationStartTime + time;
+        this.animationRequestId = window.requestAnimationFrame(this.requestAnimationFrameCallback);
+    }
+
+    stop() {
+        if (this.animationRequestId === null) {
+            return;
+        }
+
+        window.cancelAnimationFrame(this.animationRequestId);
+        this.animationRequestId = null;
+    }
+
+    onAnimationFrame(time) {
+        if (time >= this.animationEndTime) {
+            window.scroll(this.animationEndX, this.animationEndY);
+            this.animationRequestId = null;
+            return;
+        }
+
+        const t = WindowScroll.easeInOutCubic((time - this.animationStartTime) / (this.animationEndTime - this.animationStartTime));
+        window.scroll(
+            WindowScroll.lerp(this.animationStartX, this.animationEndX, t),
+            WindowScroll.lerp(this.animationStartY, this.animationEndY, t)
+        );
+
+        this.animationRequestId = window.requestAnimationFrame(this.requestAnimationFrameCallback);
+    }
+
+    get x() {
+        return window.scrollX || window.pageXOffset;
+    }
+
+    get y() {
+        return window.scrollY || window.pageYOffset;
+    }
+
+    static easeInOutCubic(t) {
+        if (t < 0.5) {
+            return (4.0 * t * t * t);
+        } else {
+            t = 1.0 - t;
+            return 1.0 - (4.0 * t * t * t);
+        }
+    }
+
+    static lerp(start, end, percent) {
+        return (end - start) * percent + start;
+    }
+}