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- §

  # ConicGradient factory

  Scrawl-canvas ConicGradient objects implement the Canvas API’s createConicGradient method. The resulting CanvasGradient object can be used by any Scrawl-canvas entity as its `fillStyle` or `strokeStyle`.

  - Most gradient-related functionality has been coded up in the styles mixin, and is documented there.
  - ConicGradients fully participate in the Scrawl-canvas packet system, thus can be saved, restored, cloned, killed, etc.
  - ConicGradients can be animated in a variety of ways; the can act as target objects for Scrawl-canvas Tweens.

  ConicGradients can be applied to an entity in two different ways, depending on the entity’s `lockFillStyleToEntity` and `lockStrokeStyleToEntity` attribute flags:

  - Cell-locked ConicGradients will cover the entire Cell; an entity moved from one part of the display to another will show different parts of the gradient
  - Entity-locked ConicGradients display their entire color range on the entity, move with the entity and even rotate with the entity.

  TO NOTE: this is an experimental technology; most browsers do not (yet) support conic gradients for canvases, only in CSS. In these browsers, the gradient will return a solid, transparent color. To see the effect, enable the appropriate flags in the browser:

  - Chrome browsers< - from version 86: this feature is behind the #new-canvas-2d-api preferences. To change preferences in Chrome, visit chrome://flags
  - Firefox browsers - From version 86: this feature is behind the canvas.createConicGradient.enabled preferences. To change preferences in Firefox, visit about:config
  - Other browsers - currently no signals about support. See the MDN createConicGradient() page for further details
- §

  #### Demos:

  - Canvas-049 - Conic gradients
- §

  #### Imports

      import { constructors } from '../core/library.js';

      import { doCreate, mergeOver, pushUnique, Ωempty } from '../core/utilities.js';

      import baseMix from '../mixin/base.js';
      import stylesMix from '../mixin/styles.js';

      import { _radian, BLANK, STYLES, T_CONIC_GRADIENT } from '../core/shared-vars.js';

- §

  #### ConicGradient constructor

      const ConicGradient = function (items = Ωempty) {

          this.stylesInit(items);
          return this;
      };

- §

  #### ConicGradient prototype

      const P = ConicGradient.prototype = doCreate();
      P.type = T_CONIC_GRADIENT;
      P.lib = STYLES;
      P.isArtefact = false;
      P.isAsset = false;

- §

  #### Mixins

      baseMix(P);
      stylesMix(P);

- §

  #### ConicGradient attributes

  - Attributes defined in the base mixin: name.
  - Attributes defined in the styles mixin: start, end, palette, paletteStart, paletteEnd, cyclePalette.
  - Attributes defined in the Palette factory: colors, cyclic.

      const defaultAttributes = {

- §

  ConicGradients calculate their gradients as a sweep of color around the `start` (`startX` and `startY`) coordinate. The startAngle attribute - measured in degrees, not radians - represents the angle at which the color stop 0 occurs.

  - The sweep of colors is, by default, clockwise around the start coordinate; to reverse this, swap the gradient’s `paletteStart` and `paletteEnd` attributes.

          angle: 0,
      };
      P.defs = mergeOver(P.defs, defaultAttributes);

- §

  In addition to the attributes defined in the base and styles mixins, Gradients also pass through Palette attributes to their Palette object.

  Attributes from base mixin:

  - `name`

  Attributes from styles mixin:

  - `start`
  - `startX`
  - `startY`
  - `end`
  - `endX`
  - `endY`
  - `palette`
  - `paletteStart`
  - `paletteEnd`
  - `cyclePalette`

  Attributes from the palette factory:

  - `colors`
  - `cyclic`
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  #### Packet management

      P.packetObjects = pushUnique(P.packetObjects, ['palette']);

- §

  #### Clone management

  No additional clone functionality required

- §

  #### Kill management

  No additional kill functionality required

- §

  #### Get, Set, deltaSet

  No additional getter/setter functionality required

- §

  #### Prototype functions

- §

  `buildStyle` - internal function: creates the radial gradient on the Cell’s CanvasRenderingContext2D engine, and then adds the color stops to it.

      P.buildStyle = function (cell) {

          if (cell) {

              const engine = cell.engine;

              if (engine) {

                  if (!engine.createConicGradient) return BLANK;

                  const gradient = engine.createConicGradient(...this.gradientArgs);

                  return this.addStopsToGradient(gradient, this.paletteStart, this.paletteEnd, this.cyclePalette);
              }
          }
          return BLANK;
      };

- §

  `updateGradientArgs` - internal function

      P.updateGradientArgs = function (x, y) {

          const gradientArgs = this.gradientArgs,
              currentStart = this.currentStart,
              angle = this.angle * _radian;

          const sx = currentStart[0] + x,
              sy = currentStart[1] + y;

          gradientArgs.length = 0;
          gradientArgs.push(angle, sx, sy);
      };

- §

  #### Factory

      let graddy = scrawl.makeConicGradient({

          name: 'mygradient',

          startX: '50%',
          startY: '50%',
          angle: 90,
      });

      scrawl.makeBlock({

          name: 'myblock',

          width: '90%',
          height: '90%',
          startX: '5%',
          startY: '5%',

          fillStyle: graddy,
          strokeStyle: 'coral',
          lineWidth: 2,

          method: 'fillAndDraw',
      });

      export const makeConicGradient = function (items) {

          if (!items) return false;
          return new ConicGradient(items);
      };

      constructors.ConicGradient = ConicGradient;