1 files changed, 170 insertions, 0 deletions
diff --git a/ui/DisplayElement.js b/ui/DisplayElement.js
new file mode 100644
index 0000000..c8352ed
--- /dev/null
+++ b/ui/DisplayElement.js
@@ -0,0 +1,170 @@
+const EventEmitter = require('events')
+const exception = require('../exception')
+
+module.exports = class DisplayElement extends EventEmitter {
+  // A general class that handles dealing with screen coordinates, the tree
+  // of elements, and other common stuff.
+  //
+  // This element doesn't handle any real rendering; just layouts. Placing
+  // characters at specific positions should be implemented in subclasses.
+  //
+  // It's a subclass of EventEmitter, so you can make your own events within
+  // the logic of your subclass.
+
+  constructor() {
+    super()
+
+    this.visible = true
+
+    this.parent = null
+    this.children = []
+
+    this.x = 0
+    this.y = 0
+    this.w = 0
+    this.h = 0
+
+    this.hPadding = 0
+    this.vPadding = 0
+  }
+
+  drawTo(writable) {
+    // Writes text to a "writable" - an object that has a "write" method.
+    // Custom rendering should be handled as an override of this method in
+    // subclasses of DisplayElement.
+  }
+
+  renderTo(writable) {
+    // Like drawTo, but only calls drawTo if the element is visible. Use this
+    // with your root element, not drawTo.
+
+    if (this.visible) {
+      this.drawTo(writable)
+      this.drawChildrenTo(writable)
+      this.didRenderTo(writable)
+    }
+  }
+
+  didRenderTo(writable) {
+    // Called immediately after rendering this element AND all of its
+    // children. If you need to do something when that happens, override this
+    // method in your subclass.
+    //
+    // It's fine to draw more things to the writable here - just keep in mind
+    // that it'll be drawn over this element and its children, but not any
+    // elements drawn in the future.
+  }
+
+  fixLayout() {
+    // Adjusts the layout of children in this element. If your subclass has
+    // any children in it, you should override this method.
+  }
+
+  fixAllLayout() {
+    // Runs fixLayout on this as well as all children.
+
+    this.fixLayout()
+    for (let child of this.children) {
+      child.fixAllLayout()
+    }
+  }
+
+  drawChildrenTo(writable) {
+    // Draws all of the children to a writable.
+
+    for (let child of this.children) {
+      child.renderTo(writable)
+    }
+  }
+
+  addChild(child) {
+    // TODO Don't let a direct ancestor of this be added as a child. Don't
+    // let itself be one of its childs either!
+
+    if (child === this) {
+      throw exception(
+        'EINVALIDHIERARCHY', 'An element cannot be a child of itself')
+    }
+
+    child.parent = this
+    this.children.push(child)
+    child.fixLayout()
+  }
+
+  removeChild(child) {
+    // Removes the given child element from the children list of this
+    // element. It won't be rendered in the future. If the given element
+    // isn't a direct child of this element, nothing will happen.
+
+    if (child.parent !== this) {
+      return
+    }
+
+    child.parent = null
+    this.children.splice(this.children.indexOf(child), 1)
+    this.fixLayout()
+  }
+
+  centerInParent() {
+    // Utility function to center this element in its parent. Must be called
+    // only when it has a parent. Set the width and height of the element
+    // before centering it!
+
+    if (this.parent === null) {
+      throw new Error('Cannot center in parent when parent is null')
+    }
+
+    this.x = Math.round((this.parent.contentW - this.w) / 2)
+    this.y = Math.round((this.parent.contentH - this.h) / 2)
+  }
+
+  get root() {
+    let el = this
+    while (el.parent) {
+      el = el.parent
+    }
+    return el
+  }
+
+  get directAncestors() {
+    const ancestors = []
+    let el = this
+    while (el.parent) {
+      el = el.parent
+      ancestors.push(el)
+    }
+    return ancestors
+  }
+
+  get absX() {
+    if (this.parent) {
+      return this.parent.contentX + this.x
+    } else {
+      return this.x
+    }
+  }
+
+  get absY() {
+    if (this.parent) {
+      return this.parent.contentY + this.y
+    } else {
+      return this.y
+    }
+  }
+
+  // Where contents should be positioned.
+  get contentX() { return this.absX + this.hPadding }
+  get contentY() { return this.absY + this.vPadding }
+  get contentW() { return this.w - this.hPadding * 2 }
+  get contentH() { return this.h - this.vPadding * 2 }
+
+  get left()   { return this.x }
+  get right()  { return this.x + this.w }
+  get top()    { return this.y }
+  get bottom() { return this.y + this.h }
+
+  get absLeft()   { return this.absX }
+  get absRight()  { return this.absX + this.w - 1 }
+  get absTop()    { return this.absY }
+  get absBottom() { return this.absY + this.h - 1 }
+}