feuerwerk/src/editor/graph/graphView.ts

import type { Container, FederatedPointerEvent, FederatedWheelEvent, Graphics } from 'pixi.js';
import { clamp, drawGrid, zoomFactor } from '../../ui';
import type { Point } from '../framing';

/**
 * What every surface that shows nodes shares with the graph editor: how far it zooms, how the grid
 * is drawn and how the wheel zooms about the pointer. The graph editor and a plugin's node board
 * look and move the same because they both come through here; the Tile tab's board borrows the
 * panning and zooming.
 */

/** Spacing of the background grid – and, with snapping on, of the positions a drag can leave. */
export const GRID_STEP = 24;
export const ZOOM_LIMITS = { min: 0.25, max: 2.5 };
/** Breathing room around the framed nodes, so they do not touch the edge. */
export const FIT_MARGIN = 24;
/** Below this on-screen spacing the grid is noise rather than orientation, so it is dropped. */
const MIN_GRID_STEP = 8;

export interface GraphView {
  /** Where the graph origin sits on screen. */
  pan: Point;
  /** Screen pixels per graph unit. */
  zoom: number;
}

/**
 * The view after zooming by `factor` about a screen point, which keeps the graph point under it.
 * `limits` are the graph's own unless a surface with other content says otherwise – the tile
 * board shows 48 px tiles, which one wants to come closer to than a node graph.
 */
export function zoomedAbout(
  view: GraphView,
  at: Point,
  factor: number,
  limits: { min: number; max: number } = ZOOM_LIMITS,
): GraphView {
  const zoom = clamp(view.zoom * factor, limits.min, limits.max);
  const graphX = (at.x - view.pan.x) / view.zoom;
  const graphY = (at.y - view.pan.y) / view.zoom;
  return { pan: { x: at.x - graphX * zoom, y: at.y - graphY * zoom }, zoom };
}

/**
 * How the wheel zooms: smoothly within limits, or by a rule of the surface's own – the Tile tab
 * takes the scene view's steps. A rule returns null while the wheel has not made a step yet.
 */
export type WheelZoom =
  { min: number; max: number } | ((view: GraphView, at: Point, deltaY: number) => GraphView | null);

/**
 * Drag with any button to pan, wheel to zoom about the pointer – all a board does with the pointer
 * when its content takes none. `set` receives each new view and which gesture made it.
 */
export function panAndZoom(
  surface: Container,
  get: () => GraphView,
  set: (view: GraphView, gesture: 'pan' | 'zoom') => void,
  zoom: WheelZoom = ZOOM_LIMITS,
): void {
  let panning: { start: Point; pan: Point } | null = null;
  surface.on('pointerdown', (e: FederatedPointerEvent) => {
    panning = { start: { x: e.global.x, y: e.global.y }, pan: { ...get().pan } };
  });
  surface.on('globalpointermove', (e: FederatedPointerEvent) => {
    if (!panning) return;
    const { start, pan } = panning;
    set({ ...get(), pan: { x: pan.x + e.global.x - start.x, y: pan.y + e.global.y - start.y } }, 'pan');
  });
  surface.on('pointerup', () => (panning = null));
  surface.on('pointerupoutside', () => (panning = null));
  surface.on('wheel', (e: FederatedWheelEvent) => {
    e.preventDefault();
    const at = surface.toLocal(e.global);
    const view =
      typeof zoom === 'function'
        ? zoom(get(), at, e.deltaY)
        : zoomedAbout(get(), at, zoomFactor(e.deltaY), zoom);
    if (view) set(view, 'zoom');
  });
}

/** What a node draws beyond its box: the shadow, the pins on its edges and the ring around a drop target. */
export const NODE_OVERHANG = 12;

/**
 * Whether any of a box, with what hangs over its edges, is inside a view of `w` by `h` screen pixels.
 * A graph is mostly looked at in parts, and a node outside the picture costs as much to draw as one
 * inside it (#292).
 */
export function inView(
  box: { x: number; y: number; w: number; h: number },
  view: GraphView,
  w: number,
  h: number,
  overhang = NODE_OVERHANG,
): boolean {
  const left = (0 - view.pan.x) / view.zoom - overhang;
  const top = (0 - view.pan.y) / view.zoom - overhang;
  const right = (w - view.pan.x) / view.zoom + overhang;
  const bottom = (h - view.pan.y) / view.zoom + overhang;
  return box.x < right && box.x + box.w > left && box.y < bottom && box.y + box.h > top;
}

export function drawGraphGrid(g: Graphics, view: GraphView, w: number, h: number): void {
  g.clear();
  const step = GRID_STEP * view.zoom;
  if (step < MIN_GRID_STEP) return;
  // `pan` is where the graph origin sits on screen, but no axis lines: it marks nothing.
  drawGrid(g, { originX: view.pan.x, originY: view.pan.y, step, w, h, alpha: 0.04 });
}