= Head-Up Display (HUD)
:revnumber: 2.0
:revdate: 2020/07/24
:keywords: gui, display, documentation, hud


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image::http://www.jmonkeyengine.com/wp-content/uploads/2010/10/grapplinghook.jpg[grapplinghook.jpg,width="256",height="192",align="right"]
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A HUD (Head-Up Display) is part of a game's visual user interface. It's an overlay that displays additional information as (typically) 2-dimensional text or icons on the screen, on top of the 3D scene. Not all games have, or need a HUD. To avoid breaking the immersion and cluttering the screen, only use a HUD if it is the only way to convey certain information.

HUDs are used to supply players with essential information about the game state.

*  Status: Score, minimap, points, stealth mode, …
*  Resources: Ammunition, lives/health, time, …
*  Vehicle instruments: Cockpit, speedometer, …
*  Navigational aides: Crosshairs, mouse pointer or hand, …

You have multiple options how to create HUDs.
[cols="3", options="header"]
|===

a|Option
a|Pros
a|Cons

a|Attach elements to default guiNode:
a|Easy to learn. jMonkeyEngine built-in +++<abbr title="Application Programming Interface">API</abbr>+++ for attaching plain images and bitmap text.
a|Only basic features. +
You will have to write custom controls / buttons / effects if you need them.

a|Use advanced xref:gui/nifty_gui.adoc[Nifty GUI] integration:
a|Full-featured interactive user interface. +
Includes buttons, effects, controls. +
Supports XML and Java layouts.
a|Steeper learning curve.

a|Use user contributed +++<abbr title="Graphical User Interface">GUI</abbr>+++ libraries such as xref:contributions:gui/tonegodgui/tonegodgui.adoc[tonegodgui] or link:http://hub.jmonkeyengine.org/t/lemur-api-documentation/27209[Lemur]:
a|Both have many features that would be difficult to do with Nifty +
Includes buttons, effects, controls. +
New features are still being released
a|Are not necessarily guaranteed future updates, not as well documented

|===

Using the +++<abbr title="Graphical User Interface">GUI</abbr>+++ Node is the default approach in jme3 to create simple HUDs. If you just quickly want to display a line of text, or a simple icon on the screen, use the no-frills +++<abbr title="Graphical User Interface">GUI</abbr>+++ Node, it's easier.


== Simple HUD: GUI Node

You already know the `rootNode` that holds the 3-dimensional scene graph. jME3 also offers a 2-dimension (orthogonal) node, the `guiNode`.

This is how you use the guiNode for HUDs:

*  Create a +++<abbr title="Graphical User Interface">GUI</abbr>+++ element: a BitmapText or Picture object.
*  Attach the element to the guiNode.
*  Place the element in the orthogonal render queue using `setQueueBucket(Bucket.Gui)`.

The BitmapTexts and Pictures appear as 2 dimensional element on the screen.


[TIP]
====
By default, the guiNode has some scene graph statistics attached. To clear the guiNode before you attach your own +++<abbr title="Graphical User Interface">GUI</abbr>+++ elements, use the following methods:

[source,java]
----
setDisplayStatView(false); setDisplayFps(false);
----


====



=== Displaying Pictures in the HUD

A simple image can be displayed using `com.jme3.ui.Picture`.

[source,java]
----
Picture pic = new Picture("HUD Picture");
pic.setImage(assetManager, "Textures/ColoredTex/Monkey.png", true);
pic.setWidth(settings.getWidth()/2);
pic.setHeight(settings.getHeight()/2);
pic.setPosition(settings.getWidth()/4, settings.getHeight()/4);
guiNode.attachChild(pic);

----

When you set the last boolean in setImage() to true, the alpha channel of your image is rendered transparent/translucent.


=== Displaying Text in the HUD

You use `com.jme3.font.BitmapText` to display text on the screen.

[source,java]
----

BitmapText hudText = new BitmapText(guiFont, false);
hudText.setSize(guiFont.getCharSet().getRenderedSize());      // font size
hudText.setColor(ColorRGBA.Blue);                             // font color
hudText.setText("You can write any string here");             // the text
hudText.setLocalTranslation(300, hudText.getLineHeight(), 0); // position
guiNode.attachChild(hudText);

----

The BitmapFont object `guiFont` is a default font provided by SimpleApplication. Copy you own fonts as .fnt plus .png files into the `assets/Interface/Fonts` directory and load them like this:

[source]
----
BitmapFont myFont = assetManager.loadFont("Interface/Fonts/Console.fnt");
hudText = new BitmapText(myFont, false);
----


=== Positioning HUD Elements

*  When positioning +++<abbr title="Graphical User Interface">GUI</abbr>+++ text and images in 2D, the *bottom left corner* of the screen is `(0f,0f)`, and the *top right corner* is at `(settings.getWidth(),settings.getHeight())`.
*  If you have several 2D elements in the +++<abbr title="Graphical User Interface">GUI</abbr>+++ bucket that overlap, define their depth order by specifing a Z value. For example use `pic.move(x, y, -1)` to move the picture to the background, or `hudText.setLocalTranslation(x,y,1)` to move text to the foreground.
*  Size and length values in the orthogonal render queue are treated like pixels. A 20*20-wu big quad is rendered 20 pixels wide.


=== Displaying Geometries in the HUD

It is technically possible to attach Quads and 3D Geometries to the HUD. They show up as flat, static +++<abbr title="Graphical User Interface">GUI</abbr>+++ elements. The size unit for the guiNode is pixels, not world units. If you attach a Geometry that uses a lit Material, you must add a light to the guiNode.


[IMPORTANT]
====
If you don't see an attached object in the +++<abbr title="Graphical User Interface">GUI</abbr>+++, check it's position and material (add a light to guiNode). Also verify whether it is not too tiny to be seen. For comparison: A 1 world-unit wide cube is only 1 pixel wide when attached to the guiNode! You may need to scale it bigger.
====



=== Keeping the HUD Up-To-Date

Use the update loop to keep the content up-to-date.

[source,java]
----
public void simpleUpdate(float tpf) {
  ...
  hudText.setText("Score: " + score);
  ...
  picture.setImage(assetManager, "Interface/statechange.png", true);
  ...
}
----


== Advanced HUD: Nifty GUI

The recommended approach to create HUDs is using xref:gui/nifty_gui.adoc[Nifty GUI].

.  Lay out the +++<abbr title="Graphical User Interface">GUI</abbr>+++ in one or several Nifty XML or Java files.
.  Write the controller classes in Java.
.  Load the XML file with the controller object in your game's simpleInit() method.

The advantage of Nifty +++<abbr title="Graphical User Interface">GUI</abbr>+++ is that it is well integrated into jME and the jMonkeyEngine SDK, and that it offers all the features that you expect from a professional modern user interface.

For HUDs, you basically follow the same instructions as for creating a normal xref:gui/nifty_gui.adoc[Nifty GUI], you just don't pause the game while the HUD is up.


== See also

*  xref:sdk:plugin/fonts.adoc[Fonts]
