discover page horizontal scroll initial progress

added translate3d transform for card hover and sibling cards

implemented simple horizontal scroll animation

updated header z-index

switched z-index of cards on hover with horizontal left/right nav buttons

removed unnecessary code

added transition and states for horizontal scroll arrows, and some css tweaks and fixes

ui/js/page/discover/view.jsx

@@ -1,15 +1,180 @@
 import React from "react";
+import ReactDOM from "react-dom";
 import lbryio from "lbryio.js";
 import lbryuri from "lbryuri";
 import FileCard from "component/fileCard";
-import { BusyMessage } from "component/common.js";
+import { Icon, BusyMessage } from "component/common.js";
 import ToolTip from "component/tooltip.js";
 
-const FeaturedCategory = props => {
-  const { category, names } = props;
+class FeaturedCategory extends React.PureComponent {
+  componentWillMount() {
+    this.setState({
+      numItems: this.props.names.length,
+      canScrollPrevious: false,
+      canScrollNext: true,
+    });
+  }
+
+  handleScrollPrevious() {
+    const cardRow = ReactDOM.findDOMNode(this.refs.rowitems);
+    if (cardRow.scrollLeft > 0) {
+      // check the visible cards
+      const cards = cardRow.getElementsByTagName("section");
+      let firstVisibleCard = null;
+      let firstVisibleIdx = -1;
+      for (var i = 0; i < cards.length; i++) {
+        if (this.isCardVisible(cards[i], cardRow, false)) {
+          firstVisibleCard = cards[i];
+          firstVisibleIdx = i;
+          break;
+        }
+      }
+
+      const numDisplayed = this.numDisplayedCards(cardRow);
+      const scrollToIdx = firstVisibleIdx - numDisplayed;
+      const animationCallback = () => {
+        this.setState({
+          canScrollPrevious: cardRow.scrollLeft !== 0,
+          canScrollNext: true,
+        });
+      };
+      this.scrollCardItemsLeftAnimated(
+        cardRow,
+        scrollToIdx < 0 ? 0 : cards[scrollToIdx].offsetLeft,
+        100,
+        animationCallback
+      );
+    }
+  }
+
+  handleScrollNext() {
+    const cardRow = ReactDOM.findDOMNode(this.refs.rowitems);
+
+    // check the visible cards
+    const cards = cardRow.getElementsByTagName("section");
+    let lastVisibleCard = null;
+    let lastVisibleIdx = -1;
+    for (var i = 0; i < cards.length; i++) {
+      if (this.isCardVisible(cards[i], cardRow, true)) {
+        lastVisibleCard = cards[i];
+        lastVisibleIdx = i;
+      }
+    }
+
+    if (lastVisibleCard) {
+      const numDisplayed = this.numDisplayedCards(cardRow);
+      const animationCallback = () => {
+        // update last visible index after scroll
+        for (var i = 0; i < cards.length; i++) {
+          if (this.isCardVisible(cards[i], cardRow, true)) {
+            lastVisibleIdx = i;
+          }
+        }
+
+        this.setState({ canScrollPrevious: true });
+        if (lastVisibleIdx === cards.length - 1) {
+          this.setState({ canScrollNext: false });
+        }
+      };
+
+      this.scrollCardItemsLeftAnimated(
+        cardRow,
+        Math.min(
+          lastVisibleCard.offsetLeft,
+          cardRow.scrollWidth - cardRow.clientWidth
+        ),
+        100,
+        animationCallback
+      );
+    }
+  }
+
+  scrollCardItemsLeftAnimated(cardRow, target, duration, callback) {
+    if (!duration || duration <= diff) {
+      cardRow.scrollLeft = target;
+      if (callback) {
+        callback();
+      }
+      return;
+    }
+
+    const component = this;
+    const diff = target - cardRow.scrollLeft;
+    const tick = diff / duration * 10;
+    setTimeout(() => {
+      cardRow.scrollLeft = cardRow.scrollLeft + tick;
+      if (cardRow.scrollLeft === target) {
+        if (callback) {
+          callback();
+        }
+        return;
+      }
+      component.scrollCardItemsLeftAnimated(
+        cardRow,
+        target,
+        duration - 10,
+        callback
+      );
+    }, 10);
+  }
+
+  isCardVisible(section, cardRow, partialVisibility) {
+    // check if a card is fully or partialy visible in its parent
+    const cardRowWidth = cardRow.offsetWidth;
+    const cardRowLeft = cardRow.scrollLeft;
+    const cardRowEnd = cardRowLeft + cardRow.offsetWidth;
+    const sectionLeft = section.offsetLeft - cardRowLeft;
+    const sectionEnd = sectionLeft + section.offsetWidth;
+
+    return (
+      (sectionLeft >= 0 && sectionEnd <= cardRowWidth) ||
+      (((sectionLeft < 0 && sectionEnd > 0) ||
+        (sectionLeft > 0 && sectionLeft <= cardRowWidth)) &&
+        partialVisibility)
+    );
+  }
+
+  numDisplayedCards(cardRow) {
+    const cards = cardRow.getElementsByTagName("section");
+    const cardRowWidth = cardRow.offsetWidth;
+    // get the width of the first card and then calculate
+    const cardWidth = cards.length > 0 ? cards[0].offsetWidth : 0;
+
+    if (cardWidth > 0) {
+      return Math.ceil(cardRowWidth / cardWidth);
+    }
+
+    // return a default value of 1 card displayed if the card width couldn't be determined
+    return 1;
+  }
+
+  render() {
+    const { category, names } = this.props;
+    const leftNavClassName =
+      "card-row__nav left-nav" +
+      (this.state.canScrollPrevious ? " can-scroll" : "");
+    const rightNavClassName =
+      "card-row__nav right-nav" +
+      (this.state.canScrollNext ? " can-scroll" : "");
 
     return (
       <div className="card-row card-row--small">
+        <div className={leftNavClassName}>
+          <a
+            className="card-row__scroll-button"
+            onClick={this.handleScrollPrevious.bind(this)}
+          >
+            <Icon icon="icon-chevron-left" />
+          </a>
+        </div>
+        <div className={rightNavClassName}>
+          <a
+            className="card-row__scroll-button"
+            onClick={this.handleScrollNext.bind(this)}
+          >
+            <Icon icon="icon-chevron-right" />
+          </a>
+        </div>
         <h3 className="card-row__header">
           {category}
           {category &&
@@ -22,6 +187,7 @@ const FeaturedCategory = props => {
               className="tooltip--header"
             />}
         </h3>
+        <div ref="rowitems" className="card-row__items">
           {names &&
             names.map(name =>
               <FileCard
@@ -31,8 +197,10 @@ const FeaturedCategory = props => {
               />
             )}
         </div>
+      </div>
     );
-};
+  }
+}
 
 class DiscoverPage extends React.PureComponent {
   componentWillMount() {

ui/scss/component/_card.scss

@@ -1,6 +1,7 @@
 @import "../global";
 
 $padding-card-horizontal: $spacing-vertical * 2/3;
+$translate-card-hover: 10px;
 
 .card {
   margin-left: auto;
@@ -94,10 +95,13 @@ $card-link-scaling: 1.1;
   position: relative;
   z-index: 1;
   box-shadow: $box-shadow-focus;
-  transform: scale($card-link-scaling);
+  transform: scale($card-link-scaling) translate3d($translate-card-hover, 0, 0);
   transform-origin: 50% 50%;
   overflow-x: visible;
-  overflow-y: visible;
+  overflow-y: visible
+}
+.card--link:hover ~ .card--link {
+  transform: translate3d($translate-card-hover * 2, 0, 0);
 }
 
 .card__media {
@@ -183,26 +187,73 @@ $height-card-small: $spacing-vertical * 15;
 }
 
 .card-row {
+  + .card-row {
+    margin-top: $spacing-vertical * 1/3;
+  }
+}
+.card-row__items {
   > .card {
     vertical-align: top;
     display: inline-block;
     margin-right: $spacing-vertical / 3;
   }
-  + .card-row {
-    margin-top: $spacing-vertical * 1/3;
+  > .card:last-child {
+    margin-right: 0
   }
 }
 .card-row--small {
-  overflow-x: auto;
-  overflow-y: hidden;
+  overflow: hidden;
   white-space: nowrap;
+  position: relative;
 
   /*hacky way to give space for hover */
-  padding-left: 20px;
-  margin-left: -20px;
-  padding-right: 20px;
-  margin-right: -20px;
+  padding-right: 30px;
+}
+.card-row__items {
+  width: 100%;
+  overflow: hidden;
+
+  /*hacky way to give space for hover */
+  padding-top: 20px;
+  margin-top: -20px;
+  padding-right: 30px;
+  margin-right: -30px;
 }
 .card-row__header {
   margin-bottom: $spacing-vertical / 3;
 }
+
+.card-row__nav {
+  display: none;
+  position: absolute;
+  padding: 0 $spacing-vertical / 1.5;
+  top: ($font-size * 1.4 * $font-line-height) + ($spacing-vertical / 3);
+  height: ($width-card-small * 9 / 16) + ($font-size * 0.82 * $font-line-height * 4) + ($spacing-vertical * 4/3)
+}
+.card-row__nav .card-row__scroll-button {
+  background: $color-bg;
+  color: $color-help;
+  box-shadow: $box-shadow-layer;
+  padding: $spacing-vertical $spacing-vertical / 2;
+  position: absolute;
+  cursor: pointer;
+  left: 0;
+  top: 36%;
+  z-index: 2;
+  opacity: 0.5;
+  transition: transform 60ms ease-in-out;
+
+  &:hover {
+    opacity: 1.0;
+    transform: scale($card-link-scaling * 1.1)
+  }
+}
+.card-row__nav.left-nav {
+  left: 0;
+}
+.card-row__nav.right-nav {
+  right: 0;
+}
+.card-row__nav.can-scroll {
+  display: block
+}

ui/scss/component/_header.scss

@@ -13,7 +13,7 @@ $color-header-active: darken($color-header, 20%);
   top: 0;
   left: 0;
   width: 100%;
-  z-index: 2;
+  z-index: 3;
   padding: $spacing-vertical / 2;
   box-sizing: border-box;
 }