Make a font slider

res/css/_components.scss

@@ -7,6 +7,7 @@
 @import "./structures/_CreateRoom.scss";
 @import "./structures/_CustomRoomTagPanel.scss";
 @import "./structures/_FilePanel.scss";
+@import "./structures/_FontSlider.scss";
 @import "./structures/_GenericErrorPage.scss";
 @import "./structures/_GroupView.scss";
 @import "./structures/_HeaderButtons.scss";

res/css/structures/_FontSlider.scss

@@ -0,0 +1,88 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+.mx_fontSlider {
+    position: relative;
+    margin: 0px;
+    @mixin mx_Settings_fullWidthField;
+}
+
+.mx_fontSlider_dotContainer {
+    display: flex;
+    flex-direction: row;
+    justify-content: space-between;
+}
+
+.mx_fontSlider_bar {
+    display: flex;
+    box-sizing: border-box;
+    position: absolute;
+    height: 1rem;
+    width: 100%;
+    padding: 0 1.1rem;
+    align-items: center;
+}
+
+.mx_fontSlider_bar > hr {
+    width: 100%;
+    border: 0.2rem solid $fontSlider-background-color;
+}
+
+.mx_fontSlider_selection {
+    display: flex;
+    align-items: center;
+    width: calc(100% - 2.2rem);
+    height: 1rem;
+    position: absolute;
+}
+
+.mx_fontSlider_selectionDot {
+    transition: left 0.25s;
+    position: absolute;
+    width: 1.1rem;
+    height: 1.1rem;
+    background-color: $fontSlider-selection-color;
+    border-radius: 50%;
+    box-shadow: 0 0 6px lightgrey;
+    z-index: 10;
+}
+
+.mx_fontSlider_selection > hr {
+    transition: width 0.25s;
+    margin: 0;
+    border: 0.2rem solid $fontSlider-selection-color;
+}
+
+.mx_fontSlider_dot {
+    transition: background-color 0.2s ease-in;
+    height: 1rem;
+    width: 1rem;
+    border-radius: 50%;
+    background-color: $fontSlider-background-color;
+    margin-bottom: 5px;
+    z-index: 0;
+}
+
+.mx_fontSlider_dotActive {
+    background-color: $fontSlider-selection-color;
+}
+
+.mx_fontSlider_dotValue {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    color: $fontSlider-background-color;
+}

res/themes/light/css/_light.scss

@@ -262,6 +262,10 @@ $togglesw-off-color: #c1c9d6;
 $togglesw-on-color: $accent-color;
 $togglesw-ball-color: #fff;
 
+// FontSlider
+$fontSlider-selection-color: $accent-color;
+$fontSlider-background-color: #c1c9d6;
+
 $progressbar-color: #000;
 
 $room-warning-bg-color: $yellow-background;

src/components/structures/FontSlider.js

@@ -0,0 +1,62 @@
+/*
+Copyright 2020 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from 'react';
+
+export default class Slider extends React.Component {
+    render() {
+        let dots = this.props.values.map(v => 
+            <Dot active={v<=this.props.value} 
+                 value={this.props.displayFunc(v)} 
+                 onClick={() => this.props.updateFontSize(v)}
+                 key={v}
+            />);
+
+        let offset = this.offset(this.props.values, this.props.value);
+
+        return <div className="mx_fontSlider">
+            <div>
+                <div className="mx_fontSlider_bar">
+                    <hr />
+                    <div className="mx_fontSlider_selection">
+                        <div className="mx_fontSlider_selectionDot" style={{left: "calc(-0.55rem + " + offset + "%"}} />
+                        <hr style={{width: offset + "%"}}/>
+                    </div>
+                </div>
+                <div className="mx_fontSlider_dotContainer">
+                    {dots}
+                </div>
+            </div>
+        </div>
+    }
+        
+    offset(values, value) {
+        return  (value - values[0]) / (values[values.length - 1] - values[0]) * 100;
+    }
+}
+
+class Dot extends React.Component {
+    render () {
+        let className = "mx_fontSlider_dot" + (this.props.active? " mx_fontSlider_dotActive": "");
+
+        return <span onClick={this.props.onClick} className="mx_fontSlider_dotValue">
+            <div className={className} />
+            <div>
+                {this.props.value}
+            </div>
+        </span>
+    }
+}