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const EventEmitter = require('events')
const exception = require('../util/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 (const child of this.children) {
child.fixAllLayout()
}
}
drawChildrenTo(writable) {
// Draws all of the children to a writable.
for (const child of this.children) {
child.renderTo(writable)
}
}
addChild(child, afterIndex = this.children.length) {
// 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.splice(afterIndex, 0, 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)
}
fillParent() {
// Utility function to fill this element in its parent. Must be called
// only when it has a parent.
if (this.parent === null) {
throw new Error('Cannot fill parent when parent is null')
}
this.x = 0
this.y = 0
this.w = this.parent.contentW
this.h = this.parent.contentH
}
fitToParent() {
// Utility function to position this element so that it stays within its
// parent's bounds. Must be called only when it has a parent.
//
// This function is useful when (and only when) the right or bottom edge
// of this element may be past the right or bottom edge of its parent.
// In such a case, the element will first be moved left or up by the
// distance that its edge exceeds that of its parent, so that its edge is
// no longer past the parent's. Then, if the left or top edge of the
// element is less than zero, i.e. outside the parent, it is set to zero
// and the element's width or height is adjusted so that it does not go
// past the bounds of the parent.
if (this.x + this.w > this.parent.right) {
const offendExtent = (this.x + this.w) - this.parent.contentW
this.x -= offendExtent
if (this.x < 0) {
const offstartExtent = 0 - this.x
this.w -= offstartExtent
this.x = 0
}
}
if (this.y + this.h > this.parent.bottom) {
const offendExtent = (this.y + this.h) - this.parent.contentH
this.y -= offendExtent
if (this.y < 0) {
const offstartExtent = 0 - this.y
this.h -= offstartExtent
this.y = 0
}
}
}
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 }
}
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