User Interfaces with Alloy

Alloy is the primary toolkit with which user interfaces are created for Trial games. An integration system, trial-alloy, exists, which you should use for easier access to Alloy's UIs.

Getting Started

The first step is to define a ui subclass, which will be used to define the styling and default UI behaviour, and to act as the rendering method. The easiest way to render UI is to use a separate pass, which is then composited with your main game render.

(define-shader-pass ui (org.shirakumo.fraf.trial.alloy:base-ui)
  ((name :initform 'ui)))

You can then just enter an instance of this pass into your render pipeline. Since it is an Alloy UI instance, you can otherwise use it as you would any other Alloy UI.

The integration system takes care of translating Trial's input events into Alloy's input events, and also includes standard UI actions that you can use in your action-sets.

Note that this way the UI is rendered on a separate pass, and as such it will not automatically combine with your game render. In order to combine the two, it is recommended to use a blend-pass or similar to combine the two outputs:

(let ((game (make-instance 'render-pass))
      (ui (make-instance 'ui))
      (combine (make-instance 'blend-pass)))
  (connect (port game 'color) (port combine 'a-pass) scene)
  (connect (port ui 'color) (port combine 'b-pass) scene))


The base-ui includes a "panel system", which allows you to stack different layers of UI over each other and automatically manage all the itty gritty of focus and active action sets. Each panel is an alloy:structure and, in addition to the Alloy UI elements, also receives all of Trial's events that are posted to the UI.

Here's an example of some basic panels:

(defclass hud (org.shirakumo.fraf.trial.alloy:panel) ())

(defmethod initialize-instance :after ((hud hud) &key)
  (let ((layout (make-instance 'org.shirakumo.alloy.layouts.constraint:layout)))
    (alloy:enter "Hello!" layout :constraints `((:left 10) (:top 10) (:size 500 30)))
    (alloy:finish-structure hud layout NIL)))

(defclass menu (org.shirakumo.fraf.trial.alloy:menuing-panel) ())

(defmethod initialize-instance :after ((menu menu) &key)
  (let ((layout (make-instance 'alloy:vertical-linear-layout))
        (focus (make-instance 'alloy:vertical-focus-list))
        (quit (alloy:represent "Quit" 'alloy:button :layout-parent layout :focus-parent focus)))
    (alloy:on alloy:activate (quit)
      (quit *context*))
    (alloy:finish-structure menu layout focus)))

Panels can be shown and hiden, though often it is more convenient to use show-panel, hide-panel, and toggle-panel. If you need to access a panel specifically, you can do so with find-panel.

Any menuing-panel will take care to automatically activate the ui-actions action-set when it is shown, and restore the old action set when it is hidden. If it is important that a panel be the only one shown over the others, make it a fullscreen-panel.