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  • §

    Demo Canvas 002

    Block and wheel entity positioning (start, pivot, mimic, mouse)

  • §

    Run code

    import {
        addNativeListener,
        library as L,
        makeBlock,
        makeRender,
        makeWheel,
        observeAndUpdate,
    } from '../source/scrawl.js'
    
    import { reportSpeed, killArtefact } from './utilities.js';
  • §

    Scene setup

    let canvas = L.artefact.mycanvas;
  • §

    Create and clone block and wheel entitys. For the sake of safety and sanity, create the (reference) entitys on which other artefacts will pivot and mimic first. Then create those other artefacts.

    Note: setting this entity’s method value to none means that while it will perform all necessary calculations as part of the Display cycle, it will not complete its stamp action, thus will not appear on the display. This differs from setting its visibility attribute to false, which will make the entity skip both calculation and stamp operations

    let myPivot = makeWheel({
        name: 'mouse-pivot',
        method: 'none',
    
        startX: 'center',
        startY: 'center',
    });
    
    let myblock = makeBlock({
        name: 'base-block',
    
        width: 150,
        height: 100,
    
        handleX: 'center',
        handleY: 'center',
    
        offsetX: -140,
        offsetY: -50,
  • §

    To pivot this entity to the reference entity, we need to set both its pivot attribute (to the reference entity’s name, or the entity itself) and also set the lockTo attribute to the value ‘pivot’

        pivot: 'mouse-pivot',
        lockTo: 'pivot',
    
        fillStyle: 'darkblue',
        strokeStyle: 'gold',
        method: 'fillAndDraw',
    
        lineWidth: 6,
        lineJoin: 'round',
    
        delta: {
            roll: 0.5,
        },
    });
    
    let mywheel = makeWheel({
        name: 'base-wheel',
    
        radius: 60,
        startAngle: 35,
        endAngle: -35,
    
        handleX: 'center',
        handleY: 'center',
    
        offsetX: 140,
        offsetY: 50,
    
        pivot: 'mouse-pivot',
        lockTo: 'pivot',
    
        fillStyle: 'purple',
        strokeStyle: 'gold',
        method: 'fillAndDraw',
    
        lineWidth: 6,
        lineJoin: 'round',
    
        delta: {
            roll: -0.5,
        },
    });
    
    myblock.clone({
        name: 'pivot-block',
    
        height: 30,
    
        handleX: 'center',
        handleY: 'center',
    
        strokeStyle: 'red',
        lineWidth: 3,
        method: 'draw',
    
        pivot: 'base-block',
        lockTo: 'pivot',
    
        offsetX: 0,
        offsetY: 110,
        addPivotOffset: true,
    
        delta: {
            roll: 0,
        },
    
    }).clone({
        name: 'pivot-wheel',
    
        pivot: 'base-wheel',
        addPivotRotation: true,
    
        handleX: 0,
        handleY: '50%',
    
        offsetY: 0,
    
    }).clone({
        name: 'mimic-wheel',
  • §

    mimic is an extended form of pivot

        mimic: 'base-wheel',
        lockTo: 'mimic',
  • §

    When an entity mimics another entity’s dimensions, its own dimensions (width, height) can be added to the mimic dimensions

        width: 20,
        height: 20,
  • §

    Handles can be directly affected by mimic dimensions. If the entity adds its own dimensions to the mimics dimensions, then it may also need to add appropriate handle values to the mimic’s handle

        handleX: 10,
        handleY: 10,
    
        strokeStyle: 'darkgreen',
  • §

    The default values for the useMimic and addOwn variables is ‘false’ - including false attributes here only for convenience during development work

        useMimicDimensions: true,
        useMimicScale: true,
        useMimicStart: true,
        useMimicHandle: true,
        useMimicOffset: true,
        useMimicRotation: true,
        useMimicFlip: true,
    
        addOwnDimensionsToMimic: true,
        addOwnScaleToMimic: false,
        addOwnStartToMimic: false,
        addOwnHandleToMimic: true,
        addOwnOffsetToMimic: false,
        addOwnRotationToMimic: false,
    });
    
    mywheel.clone({
        name: 'mimic-block',
    
        mimic: 'base-block',
        lockTo: 'mimic',
    
        width: 60,
    
        strokeStyle: 'darkgreen',
        lineWidth: 3,
        method: 'draw',
    
        useMimicDimensions: true,
        useMimicScale: true,
        useMimicStart: true,
        useMimicOffset: true,
        useMimicRotation: true,
        addOwnDimensionsToMimic: true,
    });
  • §

    User interaction

    Function to check whether mouse cursor is over canvas, and lock the reference entity accordingly

    let mouseCheck = function () {
    
        let active = false;
    
        return function () {
    
            if (canvas.here.active !== active) {
    
                active = canvas.here.active;
    
                myPivot.set({
                    lockTo: (active) ? 'mouse' : 'start'
                });
            }
        };
    }();
  • §

    For this demo we will suppress touchmove functionality over the canvas

    addNativeListener('touchmove', (e) => {
    
        e.preventDefault();
        e.returnValue = false;
    
    }, canvas.domElement);
  • §

    Setup form observer functionality.

    observeAndUpdate({
    
        event: ['input', 'change'],
        origin: '.controlItem',
    
        target: canvas.base,
    
        useNativeListener: true,
        preventDefault: true,
    
        updates: {
    
            backgroundColor: ['backgroundColor', 'raw'],
            clearAlpha: ['clearAlpha', 'float'],
        },
    });
    
    const backgroundColorSelector = document.querySelector('#backgroundColor'),
        clearAlphaInput = document.querySelector('#clearAlpha');
  • §

    @ts-expect-error

    backgroundColorSelector.value = '';
  • §

    @ts-expect-error

    clearAlphaInput.value = 0.9;
  • §

    Scene animation

    Function to display frames-per-second data, and other information relevant to the demo

    const report = reportSpeed('#reportmessage', function () {
  • §

    @ts-expect-error

        return `    clearAlpha: ${clearAlphaInput.value}`;
    });
  • §

    Create the Display cycle animation

    makeRender({
    
        name: 'demo-animation',
        target: canvas,
        commence: mouseCheck,
        afterShow: report,
    });
  • §

    Development and testing

    console.log(L);
    
    console.log('Performing tests ...');
    
    killArtefact(canvas, 'mouse-pivot', 4000, () => {
    
        myPivot = L.entity['mouse-pivot'];
    
        L.entity['base-block'].set({
    
            pivot: myPivot,
            lockTo: 'pivot',
        });
    
        L.entity['base-wheel'].set({
    
            pivot: myPivot,
            lockTo: 'pivot',
        });
    });
    
    killArtefact(canvas, 'mimic-block', 6000);