Add ability to show/hide panel options

src/components/controls/panelChevron.tsx

@@ -0,0 +1,25 @@
+import React from "react";
+import styled from 'styled-components';
+import { FaChevronRight, FaChevronDown } from "react-icons/fa";
+
+const Container = styled.span`
+  padding-right: 6px;
+  color: ${(props) => props.theme.color};
+`
+
+type Props = {
+  show: boolean
+}
+
+/**
+ * An interactive chevron to show/hide a panel's options.
+ */
+export const PanelChevron = ({ show }: Props) => {
+  const icon = show ? <FaChevronDown /> : <FaChevronRight />
+
+  return (
+    <Container>
+      {icon}
+    </Container>
+  )
+}

src/components/controls/panelHeader.tsx

@@ -4,6 +4,7 @@ import { togglePanelDisplay } from "../../actions/panelDisplay";
 import { HeaderContainer } from "./styles";
 import Toggle from "./toggle";
 import { AnnotatedTitle, Title, Tooltip } from "./annotatedTitle";
+import { PanelChevron } from "./panelChevron";
 
 /** Panel identifier used internally. */
 export type PanelId = string;
@@ -15,30 +16,56 @@ type Props = {
 
   /** Indicates panel visibility. */
   panelIsVisible: boolean
+
+  /** Indicates whether there are options for the panel. */
+  hasOptions: boolean
+
+  /** Indicates options visibility. */
+  optionsAreVisible: boolean
+
+  /** Update options visibility. */
+  setOptionsAreVisible: React.Dispatch<React.SetStateAction<boolean>>
 }
 
 /**
  * A header used by all panel controls, containing an interactive title.
  */
-export const PanelHeader = ({ panel, title, tooltip, panelIsVisible }: Props) => {
+export const PanelHeader = ({ panel, title, tooltip, panelIsVisible, hasOptions, optionsAreVisible, setOptionsAreVisible }: Props) => {
   const dispatch = useAppDispatch();
 
   function togglePanelVisibility() {
     dispatch(togglePanelDisplay(panel))
   }
 
+  function toggleOptionsVisibility() {
+    setOptionsAreVisible(!optionsAreVisible);
+  }
+
   return (
-    <HeaderContainer>
-      <AnnotatedTitle
-        title={title}
-        tooltip={tooltip} />
-      <Toggle
-        display={true}
-        on={panelIsVisible}
-        callback={togglePanelVisibility}
-        label=""
-        style={{ height: "21px" }} // height from ToggleBackground. FIXME: this should be hardcoded in Toggle
-      />
+    <HeaderContainer {...(hasOptions ? {
+                            onClick: toggleOptionsVisibility,
+                            style: {cursor: "pointer"}
+                          } :
+                          {} )}>
+      <span>
+        {hasOptions &&
+          <PanelChevron
+            show={optionsAreVisible} />}
+        <AnnotatedTitle
+          title={title}
+          tooltip={tooltip} />
+      </span>
+      <span
+        // Don't allow the parent click handler to do anything here.
+        onClick={(event) => event.stopPropagation()}>
+        <Toggle
+          display={true}
+          on={panelIsVisible}
+          callback={togglePanelVisibility}
+          label=""
+          style={{ height: "21px" }} // height from ToggleBackground. FIXME: this should be hardcoded in Toggle
+        />
+      </span>
     </HeaderContainer>
   );
 };

src/components/controls/panelSection.tsx

@@ -23,15 +23,26 @@ export const PanelSection = ({ panel, title, tooltip, options=undefined }: Props
 
   const panelIsVisible = panelsToDisplay.includes(panel)
 
+  // Initially, panel visibility determines options visibility.
+  const [optionsAreVisible, setOptionsAreVisible] = React.useState(panelIsVisible);
+
+  // Subsequent panel visibility updates also determines options visibility.
+  React.useEffect(() => {
+    setOptionsAreVisible(panelIsVisible)
+  }, [panelIsVisible])
+
   return (
     <PanelSectionContainer>
       <PanelHeader
         panel={panel}
         title={title}
         tooltip={tooltip}
         panelIsVisible={panelIsVisible}
+        hasOptions={options!==undefined}
+        optionsAreVisible={optionsAreVisible}
+        setOptionsAreVisible={setOptionsAreVisible}
       />
-      {panelIsVisible && options}
+      {optionsAreVisible && options}
     </PanelSectionContainer>
   );
 };

src/components/controls/styles.js

@@ -49,7 +49,7 @@ export const PanelSectionContainer = styled.div`
 `;
 
 export const TitleAndIconContainer = styled.span`
-  display: flex;
+  display: inline-flex;
   align-items: center;
 `;