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feat: fix zoom scaling #17

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feat: fix zoom scaling #17

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3c94f38
feat: changed to multiplicative zoom instead of additive
giannatan May 19, 2026
350ff83
style: reformat w prettier
giannatan May 19, 2026
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12 changes: 9 additions & 3 deletions src/hooks/useCanvasInteraction.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,13 @@ import { useEffect, useRef, useCallback } from 'react';
import type { RefObject } from 'react';
import { useAppStore } from '../store/useAppStore';
import { screenToImage, clamp, computeFitZoom, pointInRect } from '../lib/geometry';
import { MIN_ZOOM, MAX_ZOOM, ZOOM_STEP, MIN_BOX_SIZE, HANDLE_HALFSIZE_PX } from '../lib/constants';
import {
MIN_ZOOM,
MAX_ZOOM,
ZOOM_FACTOR,
MIN_BOX_SIZE,
HANDLE_HALFSIZE_PX,
} from '../lib/constants';
import type { DragHandle, DragState } from '../lib/types';

export interface DrawingState {
Expand Down Expand Up @@ -200,8 +206,8 @@ export function useCanvasInteraction(
if (e.ctrlKey || e.metaKey) {
// Zoom toward cursor — must prevent browser zoom
e.preventDefault();
const delta = e.deltaY < 0 ? ZOOM_STEP : -ZOOM_STEP;
applyZoom(zoom + delta, e.offsetX, e.offsetY);
const factor = e.deltaY < 0 ? ZOOM_FACTOR : 1 / ZOOM_FACTOR;
applyZoom(zoom * factor, e.offsetX, e.offsetY);
} else if (e.shiftKey) {
// Horizontal pan
const d = e.deltaX || e.deltaY;
Expand Down
2 changes: 1 addition & 1 deletion src/lib/constants.ts
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Expand Up @@ -8,6 +8,6 @@ export const CLASSES: AnnotationClass[] = [

export const MIN_ZOOM = 0.25;
export const MAX_ZOOM = 5.0;
export const ZOOM_STEP = 0.1;
export const ZOOM_FACTOR = 1.1; // multiplicative zoom instead of additive
export const MIN_BOX_SIZE = 4; // px in image space, ignore smaller drags
export const HANDLE_HALFSIZE_PX = 4; // half-size of resize handles in screen pixels (8px total)
6 changes: 3 additions & 3 deletions src/store/useAppStore.ts
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
import { create } from 'zustand';
import type { Annotation, EditMode } from '../lib/types';
import { CLASSES, MIN_ZOOM, MAX_ZOOM, ZOOM_STEP } from '../lib/constants';
import { CLASSES, MIN_ZOOM, MAX_ZOOM, ZOOM_FACTOR } from '../lib/constants';
import { clamp, computeFitZoom } from '../lib/geometry';

interface AppState {
Expand Down Expand Up @@ -175,7 +175,7 @@ export const useAppStore = create<AppState>((set) => ({
canvasWidth && imageWidth
? computeFitZoom(canvasWidth, canvasHeight, imageWidth, imageHeight)
: MIN_ZOOM;
const newZoom = clamp(zoom + ZOOM_STEP, minZoom, MAX_ZOOM);
const newZoom = clamp(zoom * ZOOM_FACTOR, minZoom, MAX_ZOOM);
if (newZoom === zoom) return;
const cx = canvasWidth / 2;
const cy = canvasHeight / 2;
Expand All @@ -191,7 +191,7 @@ export const useAppStore = create<AppState>((set) => ({
canvasWidth && imageWidth
? computeFitZoom(canvasWidth, canvasHeight, imageWidth, imageHeight)
: MIN_ZOOM;
const newZoom = clamp(zoom - ZOOM_STEP, minZoom, MAX_ZOOM);
const newZoom = clamp(zoom / ZOOM_FACTOR, minZoom, MAX_ZOOM);
if (newZoom === zoom) return;
const cx = canvasWidth / 2;
const cy = canvasHeight / 2;
Expand Down
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