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* Adaptive Zoom Search
*
* This module implements the adaptive zoom search algorithm that finds the
* optimal zoom level based on detected region sizes. The algorithm starts from
* maximum zoom and reduces iteratively until a region fits nicely in the magnifier.
*
* Key features:
* - Adaptive acceptance thresholds based on smallest region size
* - Viewport clamping to map bounds
* - Region-in-viewport detection
* - Support for multi-piece regions (uses largest piece for sizing)
* - Debug bounding box tracking
*/
import type { MapData } from '../types'
import type { DetectedRegion } from '../hooks/useRegionDetection'
export interface AdaptiveZoomSearchContext {
/** Detected region objects with size and metadata */
detectedRegions: DetectedRegion[]
/** Size of the smallest detected region in pixels */
detectedSmallestSize: number
/** Cursor position in container coordinates */
cursorX: number
cursorY: number
/** Container bounding rect */
containerRect: DOMRect
/** SVG element bounding rect */
svgRect: DOMRect
/** Map data containing regions and viewBox */
mapData: MapData
/** SVG element reference for querying region paths */
svgElement: SVGSVGElement
/** Cache of largest piece sizes for multi-piece regions */
largestPieceSizesCache: Map<string, { width: number; height: number }>
/** Maximum zoom level (default: 1000) */
maxZoom?: number
/** Minimum zoom level (default: 1) */
minZoom?: number
/** Zoom step multiplier (default: 0.9 = reduce by 10% each iteration) */
zoomStep?: number
/** Whether pointer lock is active (for logging) */
pointerLocked?: boolean
}
export interface Bounds {
left: number
right: number
top: number
bottom: number
}
export interface BoundingBox {
regionId: string
x: number
y: number
width: number
height: number
importance?: number
wasAccepted?: boolean
}
export interface RegionZoomDecision {
regionId: string
importance: number
currentSize: { width: number; height: number } // Screen pixels
testedZoom: number | null // Zoom level tested for this region (null if not in viewport)
magnifiedSize: { width: number; height: number } | null // Size at tested zoom
sizeRatio: { width: number; height: number } | null // Ratio of magnified size to magnifier
wasAccepted: boolean
rejectionReason: string | null // Why this region was rejected (if applicable)
}
export interface AdaptiveZoomSearchResult {
/** The optimal zoom level found */
zoom: number
/** Whether a good zoom was found (false = using minimum zoom as fallback) */
foundGoodZoom: boolean
/** Debug bounding boxes for visualization (includes all detected regions) */
boundingBoxes: BoundingBox[]
/** Detailed decision information for each region */
regionDecisions: RegionZoomDecision[]
/** The acceptance thresholds used */
acceptanceThresholds: { min: number; max: number }
/** The region that was accepted (if any) */
acceptedRegionId: string | null
}
/**
* Calculate adaptive acceptance thresholds based on smallest region size.
*
* For ultra-small regions like Gibraltar (0.08px), we need lower acceptance
* thresholds because even at 1000× zoom they only occupy ~0.02% of the magnifier.
*
* @param smallestSize - Smallest detected region size in pixels
* @returns Min and max acceptable ratios (region size / magnifier size)
*/
export function calculateAdaptiveThresholds(smallestSize: number): {
min: number
max: number
} {
if (smallestSize < 1) {
// Sub-pixel regions (Gibraltar at 0.08px, Vatican, Monaco):
// These are so small that we want maximum zoom. Accept anything from 2% up to 40%.
// At 1000x zoom, a 0.08px region becomes 80px in a ~400px magnifier = 20%.
// We want to accept this rather than stepping down to lower zoom.
return { min: 0.02, max: 0.4 }
}
if (smallestSize < 5) {
// Tiny regions (1-5px): accept 5-25% of magnifier
return { min: 0.05, max: 0.25 }
}
// Normal small regions: accept 10-30% of magnifier
return { min: 0.1, max: 0.3 }
}
/**
* Clamp viewport bounds to map bounds.
*
* When the cursor is near the map edge, the magnified viewport may extend beyond
* the map. This function shifts the viewport to keep it within map bounds.
*
* @param viewport - Initial viewport bounds
* @param mapBounds - Map bounds
* @returns Clamped viewport bounds
*/
export function clampViewportToMapBounds(
viewport: Bounds,
mapBounds: Bounds
): Bounds & { wasClamped: boolean } {
let { left, right, top, bottom } = viewport
let wasClamped = false
// If viewport extends beyond left edge, shift it right
if (left < mapBounds.left) {
const shift = mapBounds.left - left
left += shift
right += shift
wasClamped = true
}
// If viewport extends beyond right edge, shift it left
if (right > mapBounds.right) {
const shift = right - mapBounds.right
left -= shift
right -= shift
wasClamped = true
}
// If viewport extends beyond top edge, shift it down
if (top < mapBounds.top) {
const shift = mapBounds.top - top
top += shift
bottom += shift
wasClamped = true
}
// If viewport extends beyond bottom edge, shift it up
if (bottom > mapBounds.bottom) {
const shift = bottom - mapBounds.bottom
top -= shift
bottom -= shift
wasClamped = true
}
return { left, right, top, bottom, wasClamped }
}
/**
* Check if a region overlaps with the viewport.
*
* @param regionBounds - Region bounding box in SVG coordinates
* @param viewport - Viewport bounds in SVG coordinates
* @returns True if region overlaps viewport
*/
export function isRegionInViewport(regionBounds: Bounds, viewport: Bounds): boolean {
return (
regionBounds.left < viewport.right &&
regionBounds.right > viewport.left &&
regionBounds.top < viewport.bottom &&
regionBounds.bottom > viewport.top
)
}
/**
* Calculate importance score for a region based on distance from cursor and size.
*
* Smaller regions and regions closer to cursor get higher importance scores.
* This ensures we zoom appropriately for the region the user is actually targeting.
*
* @param region - Detected region with size metadata
* @param cursorX - Cursor X in container coordinates
* @param cursorY - Cursor Y in container coordinates
* @param regionCenterX - Region center X in screen coordinates
* @param regionCenterY - Region center Y in screen coordinates
* @param containerRect - Container bounding rect
* @returns Importance score (higher = more important)
*/
function calculateRegionImportance(
region: DetectedRegion,
cursorX: number,
cursorY: number,
regionCenterX: number,
regionCenterY: number,
containerRect: DOMRect
): number {
// 1. Distance factor: Closer to cursor = more important
const cursorClientX = containerRect.left + cursorX
const cursorClientY = containerRect.top + cursorY
const distanceToCursor = Math.sqrt(
(cursorClientX - regionCenterX) ** 2 + (cursorClientY - regionCenterY) ** 2
)
// SMOOTH EDGE FALLOFF: Create a continuous importance curve
// - At cursor (0px): importance = 1.0 (maximum)
// - At 25px: importance ≈ 0.5 (half)
// - At 50px (edge): importance ≈ 0.0 (minimal, but not zero for continuity)
//
// Use smooth cubic falloff: (1 - (d/50)^3)
// This provides:
// - Slow decrease near cursor (plateau at center)
// - Faster decrease at mid-range
// - Very gradual approach to zero at edge (no discontinuity)
const normalizedDistance = Math.min(distanceToCursor / 50, 1)
const distanceWeight = Math.max(0, 1 - normalizedDistance ** 3)
// 2. Size factor: Smaller regions get boosted importance
// This ensures San Marino can be targeted even when Italy is closer to cursor
// HOWEVER: Only apply boost if region has meaningful distance weight (> 0.1)
// This prevents tiny regions at the edge from suddenly dominating
const sizeBoost = region.isVerySmall && distanceWeight > 0.1 ? 1.5 : 1.0
// Combined importance score
return distanceWeight * sizeBoost
}
/**
* Find optimal zoom level for the detected regions.
*
* Algorithm:
* 1. Start from MAX_ZOOM and reduce by ZOOM_STEP each iteration
* 2. For each zoom level, calculate the magnified viewport
* 3. Clamp viewport to map bounds
* 4. Check if any detected region is inside viewport and fits nicely
* 5. "Fits nicely" = region occupies min-max% of magnifier (adaptive thresholds)
* 6. Accept first zoom level where a region fits
* 7. If no zoom found, return MIN_ZOOM as fallback
*
* @param context - Search context with regions, dimensions, and configuration
* @returns Optimal zoom level and debug information
*/
export function findOptimalZoom(context: AdaptiveZoomSearchContext): AdaptiveZoomSearchResult {
const {
detectedRegions,
detectedSmallestSize,
cursorX,
cursorY,
containerRect,
svgRect,
mapData,
svgElement,
largestPieceSizesCache,
maxZoom = 1000,
minZoom = 1,
zoomStep = 0.9,
pointerLocked = false,
} = context
// Calculate adaptive acceptance thresholds
const thresholds = calculateAdaptiveThresholds(detectedSmallestSize)
const { min: minAcceptableRatio, max: maxAcceptableRatio } = thresholds
// Parse viewBox
const viewBoxParts = mapData.viewBox.split(' ').map(Number)
const viewBoxX = viewBoxParts[0] || 0
const viewBoxY = viewBoxParts[1] || 0
const viewBoxWidth = viewBoxParts[2] || 1000
const viewBoxHeight = viewBoxParts[3] || 1000
// Magnifier dimensions
const magnifierWidth = containerRect.width * 0.5
const magnifierHeight = magnifierWidth / 2
// Convert cursor position to SVG coordinates
const scaleX = viewBoxWidth / svgRect.width
const scaleY = viewBoxHeight / svgRect.height
// CRITICAL: Calculate minimum zoom to ensure magnified viewport doesn't exceed detection box
// Detection box is 50px, so magnified area should not show more than 50px of screen space
// At zoom Z, the magnifier shows svgRect.height/Z pixels vertically
// We need: svgRect.height/minZoom <= 50
// Therefore: minZoom >= svgRect.height/50
const calculatedMinZoom = Math.max(svgRect.height / 50, minZoom)
const cursorSvgX = (cursorX - (svgRect.left - containerRect.left)) * scaleX + viewBoxX
const cursorSvgY = (cursorY - (svgRect.top - containerRect.top)) * scaleY + viewBoxY
// Map bounds for viewport clamping
const mapBounds = {
left: viewBoxX,
right: viewBoxX + viewBoxWidth,
top: viewBoxY,
bottom: viewBoxY + viewBoxHeight,
}
// Calculate importance scores for all detected regions
// This weights regions by distance from cursor and size
const regionsWithScores = detectedRegions.map((detectedRegion) => {
const regionPath = svgElement.querySelector(`path[data-region-id="${detectedRegion.id}"]`)
if (!regionPath) {
return { region: detectedRegion, importance: 0, centerX: 0, centerY: 0 }
}
const pathRect = regionPath.getBoundingClientRect()
const regionCenterX = pathRect.left + pathRect.width / 2
const regionCenterY = pathRect.top + pathRect.height / 2
const importance = calculateRegionImportance(
detectedRegion,
cursorX,
cursorY,
regionCenterX,
regionCenterY,
containerRect
)
return {
region: detectedRegion,
importance,
centerX: regionCenterX,
centerY: regionCenterY,
}
})
// Sort by importance (highest first)
const sortedRegions = regionsWithScores.sort((a, b) => b.importance - a.importance)
// Track bounding boxes for debug visualization - add ALL detected regions upfront
const boundingBoxes: BoundingBox[] = sortedRegions
.map(({ region: detectedRegion, importance }) => {
const regionPath = svgElement.querySelector(`path[data-region-id="${detectedRegion.id}"]`)
if (!regionPath) {
return {
regionId: detectedRegion.id,
x: 0,
y: 0,
width: 0,
height: 0,
importance,
wasAccepted: false,
}
}
const pathRect = regionPath.getBoundingClientRect()
const regionSvgLeft = (pathRect.left - svgRect.left) * scaleX + viewBoxX
const regionSvgTop = (pathRect.top - svgRect.top) * scaleY + viewBoxY
return {
regionId: detectedRegion.id,
x: regionSvgLeft,
y: regionSvgTop,
width: pathRect.width * scaleX,
height: pathRect.height * scaleY,
importance,
wasAccepted: false,
}
})
.filter((bbox) => bbox.width > 0 && bbox.height > 0)
// Track detailed decision information for each region
const regionDecisions: RegionZoomDecision[] = []
let acceptedRegionId: string | null = null
// Search for optimal zoom
let optimalZoom = maxZoom
let foundGoodZoom = false
for (let testZoom = maxZoom; testZoom >= calculatedMinZoom; testZoom *= zoomStep) {
// Calculate the SVG viewport that will be shown in the magnifier at this zoom
const magnifiedViewBoxWidth = viewBoxWidth / testZoom
const magnifiedViewBoxHeight = viewBoxHeight / testZoom
// The viewport is centered on cursor position
const initialViewport = {
left: cursorSvgX - magnifiedViewBoxWidth / 2,
right: cursorSvgX + magnifiedViewBoxWidth / 2,
top: cursorSvgY - magnifiedViewBoxHeight / 2,
bottom: cursorSvgY + magnifiedViewBoxHeight / 2,
}
// Clamp viewport to stay within map bounds
const viewport = clampViewportToMapBounds(initialViewport, mapBounds)
// Check regions in order of importance (most important first)
let foundFit = false
for (const { region: detectedRegion, importance } of sortedRegions) {
const region = mapData.regions.find((r) => r.id === detectedRegion.id)
if (!region) continue
const regionPath = svgElement.querySelector(`path[data-region-id="${detectedRegion.id}"]`)
if (!regionPath) continue
// Use pre-computed largest piece size for multi-piece regions
let currentWidth: number
let currentHeight: number
const cachedSize = largestPieceSizesCache.get(detectedRegion.id)
if (cachedSize) {
// Multi-piece region: use pre-computed largest piece
currentWidth = cachedSize.width
currentHeight = cachedSize.height
} else {
// Single-piece region: use normal bounding box
const pathRect = regionPath.getBoundingClientRect()
currentWidth = pathRect.width
currentHeight = pathRect.height
}
const pathRect = regionPath.getBoundingClientRect()
// Convert region bounding box to SVG coordinates
const regionSvgLeft = (pathRect.left - svgRect.left) * scaleX + viewBoxX
const regionSvgRight = regionSvgLeft + pathRect.width * scaleX
const regionSvgTop = (pathRect.top - svgRect.top) * scaleY + viewBoxY
const regionSvgBottom = regionSvgTop + pathRect.height * scaleY
// Check if region is inside the magnified viewport
const regionBounds = {
left: regionSvgLeft,
right: regionSvgRight,
top: regionSvgTop,
bottom: regionSvgBottom,
}
const inViewport = isRegionInViewport(regionBounds, viewport)
if (!inViewport) {
// Record decision: Not in viewport at this zoom
const existingDecision = regionDecisions.find((d) => d.regionId === detectedRegion.id)
if (!existingDecision) {
regionDecisions.push({
regionId: detectedRegion.id,
importance,
currentSize: { width: currentWidth, height: currentHeight },
testedZoom: null,
magnifiedSize: null,
sizeRatio: null,
wasAccepted: false,
rejectionReason: 'Not in viewport',
})
}
continue // Skip regions not in viewport
}
// Region is in viewport - check if it's a good size
const magnifiedWidth = currentWidth * testZoom
const magnifiedHeight = currentHeight * testZoom
const widthRatio = magnifiedWidth / magnifierWidth
const heightRatio = magnifiedHeight / magnifierHeight
// If either dimension is within our adaptive acceptance range, we found a good zoom
const widthFits = widthRatio >= minAcceptableRatio && widthRatio <= maxAcceptableRatio
const heightFits = heightRatio >= minAcceptableRatio && heightRatio <= maxAcceptableRatio
if (widthFits || heightFits) {
optimalZoom = testZoom
foundFit = true
foundGoodZoom = true
acceptedRegionId = detectedRegion.id
// Zoom accepted (log removed to reduce spam)
// Mark this region's bounding box as accepted
const acceptedBox = boundingBoxes.find((bbox) => bbox.regionId === detectedRegion.id)
if (acceptedBox) {
acceptedBox.wasAccepted = true
}
// Record the acceptance decision
regionDecisions.push({
regionId: detectedRegion.id,
importance,
currentSize: { width: currentWidth, height: currentHeight },
testedZoom: testZoom,
magnifiedSize: { width: magnifiedWidth, height: magnifiedHeight },
sizeRatio: { width: widthRatio, height: heightRatio },
wasAccepted: true,
rejectionReason: null,
})
break // Found a good zoom, stop checking regions
} else {
// Record rejection: Size doesn't fit
const reason =
widthRatio < minAcceptableRatio || heightRatio < minAcceptableRatio
? 'Too small (below min threshold)'
: 'Too large (above max threshold)'
const existingDecision = regionDecisions.find((d) => d.regionId === detectedRegion.id)
if (!existingDecision) {
regionDecisions.push({
regionId: detectedRegion.id,
importance,
currentSize: { width: currentWidth, height: currentHeight },
testedZoom: testZoom,
magnifiedSize: { width: magnifiedWidth, height: magnifiedHeight },
sizeRatio: { width: widthRatio, height: heightRatio },
wasAccepted: false,
rejectionReason: reason,
})
}
}
}
if (foundFit) break // Found a good zoom level, stop searching
}
if (!foundGoodZoom) {
// Didn't find a good zoom - use calculated minimum
optimalZoom = calculatedMinZoom
}
return {
zoom: optimalZoom,
foundGoodZoom,
boundingBoxes,
regionDecisions,
acceptanceThresholds: thresholds,
acceptedRegionId,
}
}
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