Should I use an event handler or actor for adding keyboard controls for a game

Question

In Rebol3 Saphir, I am writing a game and I had been poking about with the event handler functionality as well as actors, and I was wondering whether it would be a better idea to use an event handler to take keyboard controls for the game or to add an actor into one of the GUI elements.

If I use an actor, on what level? I'm currently using an image! type for the screen. Can I add an actor to the root(layout) face so even if I click (give focus) to a button also on the GUI the focus will be off the image and it won't take keyboard controls.

Answer 1

Below is an example how you could do it...You might also use just the built-in keyboard shortcuts feature if you don't need key-up events. In such case see example with shortcut keys here: https://github.com/saphirion/documentation/blob/master/r3/r3-gui/examples/layouts/layout-15.r3

This version is modified to work with the current (09/26/13) release of R3-GUI

REBOL [
    author: "cyphre@seznam.cz"
]

load-gui

;image for game screen
img: make image! 400x400

;just some example game object
game-object: context [
    offset: 0x0
    draw-block: [
        pen red
        fill-pen white
        line-width 5
        circle offset 20
    ]
    move: func [
        delta [pair!]
    ][
        offset: offset + delta
        img/rgb: black
        ;note: this is not optimal way how to render DRAW objects
        ;but I use image! here because the asking SO user uses image! as well
        ;better way is to just use DRAWING style for DRAW based graphics
        draw img to-draw draw-block copy []
        draw-face game-screen
        ;signal true move has been executed
        return true
    ]
]

stylize [
    ;backup the original window style to be able call the original key actor
    window-orig: window []

    ;override window style with our key actor
    window: window [
        actors: [
            on-key: [
                ;execute our key controls prior to 'system' key handling
                switch arg/type [
                    key [
                        ;here you can handle key-down events
                        moved?: switch/default arg/key [
                            up [
                                game-object/move 0x-5
                            ]
                            down [
                                game-object/move 0x5
                            ]
                            left [
                                game-object/move -5x0
                            ]
                            right [
                                game-object/move 5x0
                            ]
                        ][
                            false
                        ]
                    ]
                    key-up [
                        ;here you can handle key-up events
                    ]
                ]
                ;for example filter out faces that shouldn't get the system key events (for example editable styles)
                 unless all [
                    moved?
                    guie/focal-face
                    tag-face? guie/focal-face 'edit
                 ][
                    ;handle the system key handling
                    do-actor/style face 'on-key arg 'window-orig
                ]
            ]
        ]
    ]
]

view [
    title "Custom keyboard handling (whole window)"
    text "press cursor keys to move the box"
    game-screen: image options [min-size: 400x400 max-size: 400x400]
    text 400 "focus the field below and press to see these keys are filtered out, but other keys works normally"
    field "lorem ipsum"
    when [enter] on-action [
        ;initialize game object
        game-object/move 200x200
    set-face game-screen img
    ]
]

This version uses an as-of-yet unreleased version of R3-GUI:

REBOL [
    author: "cyphre@seznam.cz"
]

;image for game screen
img: make image! 400x400

;just some example game object
game-object: context [
    offset: 0x0
    draw-block: [
        pen red
        fill-pen white
        line-width 5
        circle offset 20
    ]
    move: func [
        delta [pair!]
    ][
        offset: offset + delta
        img/rgb: black
        ;note: this is not optimal way how to render DRAW objects
        ;but I use image! here because the asking SO user uses image! as well
        ;better way is to just use DRAWING style for DRAW based graphics
        draw img to-draw draw-block copy []
        draw-face game-screen
        ;signal true move has been executed
        return true
    ]
]

stylize [
    ;backup the original window style to be able call the original key actor
    window-orig: window []

    ;override window style with our key actor
    window: window [
        actors: [
            on-key: [
                ;execute our key controls prior to 'system' key handling
                switch arg/type [
                    key [
                        ;here you can handle key-down events
                        moved?: switch/default arg/key [
                            up [
                                game-object/move 0x-5
                            ]
                            down [
                                game-object/move 0x5
                            ]
                            left [
                                game-object/move -5x0
                            ]
                            right [
                                game-object/move 5x0
                            ]
                        ][
                            false
                        ]
                    ]
                    key-up [
                        ;here you can handle key-up events
                    ]
                ]
                ;for example filter out faces that shouldn't get the system key events (for example editable styles)
                 unless all [
                    moved?
                    guie/focal-face
                    tag-face? guie/focal-face 'edit
                 ][
                    ;handle the system key handling
                    do-actor/style face 'on-key arg 'window-orig
                ]
            ]
        ]
    ]
]

view [
    title "Custom keyboard handling (whole window)"
    text "press cursor keys to move the box"
    game-screen: image img options [min-size: 400x400 max-size: 400x400]
    text 400 "focus the field below and press to see these keys are filtered out, but other keys works normally"
    field "lorem ipsum"
    when [enter] on-action [
        ;initialize game object
        game-object/move 200x200
    ]
]