Aislo/B07_DesignDetail/openwebcad/src/helpers/scene-cache.ts

import type { ScreenCanvasDrawController } from '../drawControllers/screenCanvas.drawController';
import {
	getGridEnabled,
	getHighlightedEntityIds,
	setHighlightedEntityIds,
} from '../state';
import { drawEntities } from './draw-functions';
import { getSceneVersion } from './scene-version';
import { queryEntitiesInBox } from './spatial-index';

/**
 * Static scene cache: all entities are rendered once into an offscreen canvas.
 * While panning, the cached bitmap is blitted at a pixel offset instead of
 * re-stroking every entity each frame. The cache is rebuilt when the scene
 * version bumps (entities/layers/selection changed), when zoom or canvas size
 * changes, or after the pan offset has settled for PAN_SETTLE_MS.
 *
 * Highlight is intentionally NOT baked into the cache (it changes on every
 * mouse move) — draw.ts re-draws highlighted entities on top each frame.
 */
const PAN_SETTLE_MS = 120;

interface RenderedParams {
	version: number;
	scale: number;
	offsetX: number;
	offsetY: number;
	sizeX: number;
	sizeY: number;
}

let offscreenCanvas: HTMLCanvasElement | null = null;
let rendered: RenderedParams | null = null;
let prevOffsetX = Number.NaN;
let prevOffsetY = Number.NaN;
let lastOffsetChangeAt = 0;

export const scenePerf = {
	sceneRebuilds: 0,
	lastRebuildMs: 0,
	avgFrameMs: 0,
};
(window as unknown as Record<string, unknown>).__aisloCadPerf = scenePerf;

export function invalidateSceneCache(): void {
	rendered = null;
}

/**
 * Viewport culling: only entities whose bbox intersects the current view
 * (expanded by one viewport on each side, so short pans stay covered by the
 * blit before the settle-rebuild) are rendered into the scene cache.
 */
function sceneEntitiesForViewport(drawController: ScreenCanvasDrawController) {
	const size = drawController.getCanvasSize();
	const scale = drawController.getScreenScale();
	const offset = drawController.getScreenOffset();
	const viewWidth = size.x / scale;
	const viewHeight = size.y / scale;
	return queryEntitiesInBox(
		offset.x - viewWidth,
		offset.y - viewHeight,
		offset.x + 2 * viewWidth,
		offset.y + 2 * viewHeight
	);
}

function rebuildScene(drawController: ScreenCanvasDrawController): void {
	const size = drawController.getCanvasSize();
	if (!offscreenCanvas) {
		offscreenCanvas = document.createElement('canvas');
	}
	if (offscreenCanvas.width !== size.x || offscreenCanvas.height !== size.y) {
		offscreenCanvas.width = Math.max(1, size.x);
		offscreenCanvas.height = Math.max(1, size.y);
	}
	const offscreenContext = offscreenCanvas.getContext('2d');
	if (!offscreenContext) return;

	const startedAt = performance.now();
	// Exclude the (rapidly changing) hover highlight from the baked bitmap.
	const savedHighlight = getHighlightedEntityIds();
	if (savedHighlight.length) setHighlightedEntityIds([]);
	drawController.withContext(offscreenContext, () => {
		drawController.clear();
		// Style-run batching + sub-pixel decimation: one stroke per style run
		drawController.beginBatch();
		drawEntities(drawController, sceneEntitiesForViewport(drawController));
		drawController.endBatch();
	});
	if (savedHighlight.length) setHighlightedEntityIds(savedHighlight);

	scenePerf.lastRebuildMs = performance.now() - startedAt;
	scenePerf.sceneRebuilds++;

	const offset = drawController.getScreenOffset();
	rendered = {
		version: getSceneVersion(),
		scale: drawController.getScreenScale(),
		offsetX: offset.x,
		offsetY: offset.y,
		sizeX: size.x,
		sizeY: size.y,
	};
}

/**
 * Draw the static scene: rebuild the cache when needed, otherwise blit the
 * cached bitmap (shifted by the pan delta). Called once per frame by draw().
 */
export function drawScene(drawController: ScreenCanvasDrawController, now: number): void {
	const size = drawController.getCanvasSize();
	const scale = drawController.getScreenScale();
	const offset = drawController.getScreenOffset();

	if (offset.x !== prevOffsetX || offset.y !== prevOffsetY) {
		lastOffsetChangeAt = now;
		prevOffsetX = offset.x;
		prevOffsetY = offset.y;
	}

	const paramsChanged =
		!rendered ||
		rendered.version !== getSceneVersion() ||
		rendered.scale !== scale ||
		rendered.sizeX !== size.x ||
		rendered.sizeY !== size.y;
	const offsetChanged =
		!!rendered && (rendered.offsetX !== offset.x || rendered.offsetY !== offset.y);

	// Grid lines are screen-fixed (drawn in clear()), so blitting a shifted
	// bitmap would drag the grid along — always re-render while grid is on.
	if (paramsChanged || getGridEnabled() || (offsetChanged && now - lastOffsetChangeAt >= PAN_SETTLE_MS)) {
		rebuildScene(drawController);
	}

	if (!offscreenCanvas || !rendered) return;
	// screenX = (worldX - offsetX) * scale, canvasY is y-flipped afterwards:
	// content shifts left when offset.x grows, down when offset.y grows.
	const dx = (rendered.offsetX - offset.x) * scale;
	const dy = (offset.y - rendered.offsetY) * scale;
	drawController.blitImage(offscreenCanvas, dx, dy);
}