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- §

  # Demo Particles 008

  Net entity: generation and basic functionality, including Spring objects

- §

  Run code

      import * as scrawl from '../source/scrawl.js';

      import { reportSpeed } from './utilities.js';

- §

  Import image from DOM

      scrawl.importDomImage('.flowers');

- §

  #### Scene setup

      const canvas = scrawl.library.artefact.mycanvas;

- §

  For this Demo, we are creating a flag and pinning it to a pole. This is the pole.

      scrawl.makeLine({

          name: 'flagpole',

          startX: 'center',
          startY: 30,
          endX: 'center',
          endY: 'bottom',

          lineWidth: 8,
          lineCap: 'round',
          strokeStyle: 'brown',

          method: 'draw',
      })

- §

  #### Particle physics animation scene

- §

  Create a World object which we can then assign to the Net entity

      const myWorld = scrawl.makeWorld({

          name: 'demo-world',
          tickMultiplier: 2,

          userAttributes: [
              {
                  key: 'wind',
                  defaultValue: 0,
              },
          ],
      });

- §

  Create a ‘wind’ force; we will update the wind direction/strength as part of the Display cycle

      scrawl.makeForce({

          name: 'wind',
      /* eslint-disable-next-line */
          action: (particle, world, host) => {

              particle.load.vectorAdd({

- §

  @ts-expect-error

                  x: world.wind,
                  y: 0,
              });
          },
      });

      const changeWind = function () {

- §

  @ts-expect-error

          let newWind = myWorld.wind + Math.random() - 0.5;

          if (newWind < -15) newWind = -15;
          if (newWind > 15) newWind = 15;

          myWorld.set({

- §

  @ts-expect-error

              wind: newWind,
          });
      };

- §

  Create a Net entity

      const myNet = scrawl.makeNet({

          name: 'test-net',

- §

  Every net must be associated with a World object. The attribute’s value can be the World object’s String name value, or the object itself

          world: myWorld,

- §

  The entity’s `start` coordinates determine where the first pin will be placed on the canvas

          startX: 'center',
          startY: 40,

- §

  The Net entity comes with four pre-defined `generate` functions - we will be testing ‘weak-net’ and ‘strong-net’ in this demo.

  - We can define our own generate function if the pre-defined functions do not meet our needs.

          generate: 'weak-net',

- §

  The `postGenerate` function runs immediately after the `generate` function has created all of the Net entity’s Particle and Spring objects.

  - If the `generate` function has defined particles and/or springs that we do not need, we can kill them here
  - We can also set the attributes of specified Particles, including making them static (immobile, unaffected by forces and springs applied to them)

          postGenerate: function () {

- §

  Names for ‘weak-net’ and ‘strong-net’ Particles are consistent: `${Net-entity-name}-${row-number}-${column-number}`

              const regex = RegExp('.*(-0-0|-4-0|-9-0)$');

- §

  @ts-expect-error

              this.particleStore.forEach(p => {

                  if (regex.test(p.name)) {

- §

  Change the appearance of the selected Particles, and remove the forces acting on them

                      p.set({
                          fill: 'black',
                          stroke: 'black',
                          forces: [],
                      });

- §

  Prevent Springs associated with the selected Particles from moving them @ts-expect-error

                      this.springs.forEach(s => {

                          if (s && s.particleFrom && s.particleFrom.name === p.name) {

                              s.particleFromIsStatic = true;
                          }
                          if (s && s.particleTo && s.particleTo.name === p.name) {

                              s.particleToIsStatic = true;
                          }
                      })
                  }
              });
          },

- §

  We tell the Net entity how many rows and columns of Particles we want it to create

          rows: 10,
          columns: 14,

- §

  The distance between rows and columns can be set using either absolute (px) Number values, or relative % String values

          rowDistance: 15,
          columnDistance: '5%',

- §

  We can get the Net entity to display its springs

          showSprings: true,
          showSpringsColor: 'green',

- §

  Particle physics attributes

          mass: 1,
          forces: ['gravity', 'wind'],
          engine: 'runge-kutta',
          damperConstant: 5,

- §

  We can assign an artefact that we will be using for the particle animation, or we can define it here as part of the Net factory

          artefact: scrawl.makeWheel({

              name: 'particle-wheel',
              radius: 3,

              handle: ['center', 'center'],

              method: 'fillThenDraw',
              fillStyle: 'gold',
              strokeStyle: 'blue',

              visibility: false,

              globalAlpha: 1,

              noUserInteraction: true,
              noPositionDependencies: true,
              noFilters: true,
              noDeltaUpdates: true,
          }),

- §

  The `stampAction` function describes the steps that our Net will take to draw each of its particles (and springs, hit regions) onto the host canvas screen.

          stampAction: function (artefact, particle, host) {

              const [ , , ...start] = particle.history[0];

              artefact.simpleStamp(host, {
                  start,
                  fillStyle: particle.fill,
                  strokeStyle: particle.stroke,
              });
          },
      });

      scrawl.makePicture({

          name: 'my-flower',
          asset: 'iris',

          copyStartX: 0,
          copyStartY: 0,

          copyWidth: '100%',
          copyHeight: '100%',

          visibility: false,
      });

- §

  #### 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 `    Tick multiplier: ${tickMultiplier.value}\n    Particle mass: ${mass.value}\n    Rest length multiplier: ${restLength.value}\n    Wind speed: ${myWorld.wind.toFixed(2)}\n    Spring constant: ${springConst.value}\n    Damper constant: ${damperConst.value}`;
      });

- §

  Create the Display cycle animation

      scrawl.makeRender({

          name: 'demo-animation',
          target: canvas,
          commence: changeWind,
          afterShow: report,
      });

- §

  #### User interaction

  Setup form observer functionality

      const updateSprings = function (e) {

          if (e && e.target && e.target.id) {

              if (e.target.id === 'springConstant') myNet.set({ springConstant: parseFloat(e.target.value)});
              if (e.target.id === 'damperConstant') myNet.set({ damperConstant: parseFloat(e.target.value)});
              if (e.target.id === 'restLength') myNet.set({ restLength: parseFloat(e.target.value)});
              if (e.target.id === 'generate') myNet.set({ generate: e.target.value});
              if (e.target.id === 'engine') myNet.set({ engine: e.target.value});
              if (e.target.id === 'mass') myNet.set({ mass: parseFloat(e.target.value)});
              if (e.target.id === 'tickMultiplier') myWorld.set({ tickMultiplier: parseFloat(e.target.value)});

              myNet.restart();
          }
      };
      scrawl.addNativeListener(['input', 'change'], updateSprings, '.controlItem');

      const springConst = document.querySelector('#springConstant'),
          mass = document.querySelector('#mass'),
          restLength = document.querySelector('#restLength'),
          tickMultiplier = document.querySelector('#tickMultiplier'),
          damperConst = document.querySelector('#damperConstant');

- §

  @ts-expect-error

      springConst.value = 50;

- §

  @ts-expect-error

      damperConst.value = 5;

- §

  @ts-expect-error

      restLength.value = 1;

- §

  @ts-expect-error

      mass.value = 1;

- §

  @ts-expect-error

      tickMultiplier.value = 2;

- §

  @ts-expect-error

      document.querySelector('#generate').value = 'weak-net';

- §

  @ts-expect-error

      document.querySelector('#engine').value = 'runge-kutta';

- §

  #### Development and testing

      console.log(scrawl.library);