Enhancement: options showIf

helper.js

@@ -1,2 +1,38 @@
-export function makeUtilityButton() {
+// `items` is an array of which `item` is a member
+// `item` must let us read/write property `hidden`
+// `parentEl` is the containing element for `itemEl`
+// `itemEl` is the 
+export function show({items, item, parentEl, itemEl}) {
+  if (items.length < 2) {
+    parentEl.appendChild(itemEl);
+    return;
+  }
+  // To determine placement,
+  // Start with our index in the toolbar tools;
+  // iterate through toolbar tools before this one, 
+  // and subtract hidden ones from the index.
+
+  let countHidden = 0;
+  let index = items.indexOf(item);
+  for (let i = 0; i < index; i++) {
+    const sibling = items[i];
+    if (sibling.hidden) countHidden += 1;
+  }
+  index -= countHidden;
+
+  // Now we need to find our place.
+  // Add to parent using insertBefore.
+  let idx = 0;
+  let nextEl = parentEl.firstChild;
+  while (idx < index) {
+    nextEl = nextEl.nextSibling;
+    idx += 1;
+  }
+  parentEl.insertBefore(itemEl, nextEl);
+  item.hidden = false;
+}
+
+export function hide({item, parentEl, itemEl}) {
+  parentEl.removeChild(itemEl);
+  item.hidden = true;
 }

sim-options.js

@@ -8,9 +8,9 @@ export const simOptions = {
     velocity: ['Velocity Vectors', 'boolean', true],
     acceleration: ['Accel Vectors', 'boolean', true],
     traces: ['Path Traces', 'boolean', true],
-    dashedTraces: ['Dashed', 'boolean', false, {tall: true, hideUnless: 'display.traces'}],
-    velocityScale: ['Velocity<br>Vec Scale', 'number', 80, {hideUnless: 'display.velocity'}],
-    accelerationScale: ['Accel<br>Vec Scale', 'number', 800, {hideUnless: 'display.acceleration'}],
+    dashedTraces: ['Dashed', 'boolean', false, {tall: true, showIf: 'display.traces'}],
+    velocityScale: ['Velocity<br>Vec Scale', 'number', 80, {showIf: 'display.velocity'}],
+    accelerationScale: ['Accel<br>Vec Scale', 'number', 800, {showIf: 'display.acceleration'}],
     zoomVectors: ['Zoom Vectors', 'boolean', true]
   },
   compensate: {

tool.js

@@ -9,6 +9,7 @@ import {
 export class Tool {
   container = undefined;
   sim = undefined;
+  hidden = false;
 
   constructor() {
     const div = document.createElement('div');

tool/options.js

@@ -1,45 +1,92 @@
 // Options picker
 import {
-  TOOL_INFO_CLASSNAME,
   OPTION_GROUP_CLASSNAME,
-  WIDE_CLASSNAME,
   TALL_CLASSNAME,
+  TOOL_INFO_CLASSNAME,
+  WIDE_CLASSNAME,
 } from '../config.js';
-import { Tool } from '../tool.js';
+import {Tool} from '../tool.js';
+import {show, hide} from '../helper.js';
 
 export class OptionsTool extends Tool {
-  sections = undefined;
+  sectionNames = undefined;
+  groups = {};
 
-  constructor(sections) {
+  constructor(sectionNames) {
     super();
-    this.sections = sections;
+    this.sectionNames = sectionNames;
   }
 
   setContainer(container) {
     super.setContainer(container);
-    for (const sectionName of this.sections) {
-      const option = this.sim.options.getSection(sectionName);
-      const item = this.visitItem(option);
+    // Initialize
+    for (const sectionName of this.sectionNames) {
+      const group = this.sim.options.getSection(sectionName);
+      const item = this.visitItem(group);
       this.div.appendChild(item);
     }
   }
 
+  // For now, `showIf` must be the name of a boolean property, with optional negation
+  shouldShow(option) {
+    if (option.showIf === undefined) return true;
+    const {name, value} = this.deconstructOption(option.showIf);
+    return this.sim.getOption(name) === value;
+  }
+
+  deconstructOption(showIf) {
+    let name = showIf;
+    let value = true;
+    if (name.startsWith('!')) {
+      value = false;
+      name = name.slice(1);
+    }
+    return {name, value};
+  }
+
   visitItem(item, path) {
     path = [path, item.name].filter(x => !!x).join('.');
     switch (item.type) {
       case 'group': {
-        const group = document.createElement('div');
-        group.classList.add(OPTION_GROUP_CLASSNAME);
+        const groupEl = document.createElement('div');
+        groupEl.classList.add(OPTION_GROUP_CLASSNAME);
+        const group = {groupEl, items: []};
+        this.groups[path] = group;
         if (item.title) {
           const heading = document.createElement('h3');
           heading.innerHTML = item.title;
-          group.appendChild(heading);
+          groupEl.appendChild(heading);
+          groupEl.items.push({itemEl: heading});
         }
         for (const next of item.items) {
-          const child = this.visitItem(next, path);
-          group.appendChild(child);
+          const optionEl = this.visitItem(next, path);
+          // const option = {itemEl: optionEl};
+          group.items.push(next);
+          if (this.shouldShow(next)) {
+            groupEl.appendChild(optionEl);
+          }
+          if (next.showIf) {
+            const {name} = this.deconstructOption(next.showIf);
+            this.sim.onOptionSet(name, () => {
+              if (this.shouldShow(next)) {
+                show({
+                  items: group.items,
+                  item: next,
+                  parentEl: groupEl,
+                  itemEl: optionEl,
+                });
+              } else {
+                hide({
+                  item: next,
+                  parentEl: groupEl,
+                  itemEl: optionEl,
+                });
+              }
+            });
+          }
+
         }
-        return group;
+        return groupEl;
       }
       case 'boolean': {
         const button = document.createElement('button');