Make a font slider

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>
+    }
+}