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  • §

    The Display cycle

    Scrawl-canvas breaks down the Display cycle into three parts: clear; compile; and show. These can be triggered either as a single, combined render operation, or separately as-and-when needed.

    The order in which DOM stack and canvas elements are processed during the display cycle can be changed by setting that element’s controller’s order attribute to a higher or lower integer value; elements are processed (in batches) from lowest to highest order value

    Each display cycle function is a normal Javascript function, invoked with no arguments and returning no status

    Note that Scrawl-canvas supplies a convenience function - makeRender() - for automating the process of creating an animation object to handle the Display cycle

  • §

    Imports

    import { artefact } from "./library.js";
    
    import { getSortedRootElements } from '../helper/document-root-elements.js';
  • §

    Shared constants

    import { CLEAR } from '../helper/shared-vars.js';
  • §

    Local constants

    const COMPILE = 'compile',
        RENDER = 'render',
        SHOW = 'show';
  • §

    Helper functions coordinate the actions required to complete a display cycle

    const displayCycleHelper = function (items) {
    
        if (items.length) return items;
        return getSortedRootElements();
    };
    
    const displayCycleBatchProcess = function (rootWrappers, method) {
    
        let i, iz, item;
    
        for (i = 0, iz = rootWrappers.length; i < iz; i++) {
    
            item = artefact[rootWrappers[i]];
    
            if (item && item[method]) item[method]();
        }
    };
  • §
    Clear
    • For canvas artefacts, clear its Cell assets’ display (reset all pixels to 0, or the designated background color) ready for them to be redrawn
    • For stack artefacts - no action required
  • §

    Exported function (to modules and scrawl object).

    export const clear = function (...items) {
    
        const wrappers = displayCycleHelper(items);
        displayCycleBatchProcess(wrappers, CLEAR);
    };
  • §
    Compile
    • For both canvas and stack artefacts, perform necessary entity/element positional calculations
    • Additionally for canvas artefacts, stamp associated entitys onto the canvas’s constituent cell assets
  • §

    Exported function (to modules and scrawl object).

    export const compile = function (...items) {
    
        const wrappers = displayCycleHelper(items);
        displayCycleBatchProcess(wrappers, COMPILE);
    };
  • §
    Show
    • For canvas artefacts, stamp additional ‘layer’ canvases onto the base canvas, then copy the base canvas onto the display canvas
    • For stack artefacts - invoke the domShow function, if any of its constituent elements require DOM-related updating
  • §

    Exported function (to modules and scrawl object).

    export const show = function (...items) {
    
        const wrappers = displayCycleHelper(items);
        displayCycleBatchProcess(wrappers, SHOW);
    };
  • §
    Render
    • Orchestrate the clear, compile and show actions on each stack and canvas DOM element
  • §

    Exported function (to modules and scrawl object).

    export const render = function (...items) {
    
        const wrappers = displayCycleHelper(items);
        displayCycleBatchProcess(wrappers, RENDER);
    };