1 files changed, 110 insertions, 0 deletions
diff --git a/ext/js/dom/scroll-element.js b/ext/js/dom/scroll-element.js
new file mode 100644
index 00000000..173ce499
--- /dev/null
+++ b/ext/js/dom/scroll-element.js
@@ -0,0 +1,110 @@
+/*
+ * Copyright (C) 2019-2021  Yomichan Authors
+ *
+ * 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 <https://www.gnu.org/licenses/>.
+ */
+
+class ScrollElement {
+    constructor(node) {
+        this._node = node;
+        this._animationRequestId = null;
+        this._animationStartTime = 0;
+        this._animationStartX = 0;
+        this._animationStartY = 0;
+        this._animationEndTime = 0;
+        this._animationEndX = 0;
+        this._animationEndY = 0;
+        this._requestAnimationFrameCallback = this._onAnimationFrame.bind(this);
+    }
+
+    get x() {
+        return this._node !== null ? this._node.scrollLeft : window.scrollX || window.pageXOffset;
+    }
+
+    get y() {
+        return this._node !== null ? this._node.scrollTop : window.scrollY || window.pageYOffset;
+    }
+
+    toY(y) {
+        this.to(this.x, y);
+    }
+
+    toX(x) {
+        this.to(x, this.y);
+    }
+
+    to(x, y) {
+        this.stop();
+        this._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;
+    }
+
+    // Private
+
+    _onAnimationFrame(time) {
+        if (time >= this._animationEndTime) {
+            this._scroll(this._animationEndX, this._animationEndY);
+            this._animationRequestId = null;
+            return;
+        }
+
+        const t = this._easeInOutCubic((time - this._animationStartTime) / (this._animationEndTime - this._animationStartTime));
+        this._scroll(
+            this._lerp(this._animationStartX, this._animationEndX, t),
+            this._lerp(this._animationStartY, this._animationEndY, t)
+        );
+
+        this._animationRequestId = window.requestAnimationFrame(this._requestAnimationFrameCallback);
+    }
+
+    _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);
+        }
+    }
+
+    _lerp(start, end, percent) {
+        return (end - start) * percent + start;
+    }
+
+    _scroll(x, y) {
+        if (this._node !== null) {
+            this._node.scrollLeft = x;
+            this._node.scrollTop = y;
+        } else {
+            window.scroll(x, y);
+        }
+    }
+}