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Pinch zoom implementation for PDF.js viewer
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<!-- Goes into viewer.html just before ending </body> --> | |
<script> | |
let pinchZoomEnabled = false; | |
function enablePinchZoom(pdfViewer) { | |
let startX = 0, startY = 0; | |
let initialPinchDistance = 0; | |
let pinchScale = 1; | |
const viewer = document.getElementById("viewer"); | |
const container = document.getElementById("viewerContainer"); | |
const reset = () => { startX = startY = initialPinchDistance = 0; pinchScale = 1; }; | |
// Prevent native iOS page zoom | |
//document.addEventListener("touchmove", (e) => { if (e.scale !== 1) { e.preventDefault(); } }, { passive: false }); | |
document.addEventListener("touchstart", (e) => { | |
if (e.touches.length > 1) { | |
startX = (e.touches[0].pageX + e.touches[1].pageX) / 2; | |
startY = (e.touches[0].pageY + e.touches[1].pageY) / 2; | |
initialPinchDistance = Math.hypot((e.touches[1].pageX - e.touches[0].pageX), (e.touches[1].pageY - e.touches[0].pageY)); | |
} else { | |
initialPinchDistance = 0; | |
} | |
}); | |
document.addEventListener("touchmove", (e) => { | |
if (initialPinchDistance <= 0 || e.touches.length < 2) { return; } | |
if (e.scale !== 1) { e.preventDefault(); } | |
const pinchDistance = Math.hypot((e.touches[1].pageX - e.touches[0].pageX), (e.touches[1].pageY - e.touches[0].pageY)); | |
const originX = startX + container.scrollLeft; | |
const originY = startY + container.scrollTop; | |
pinchScale = pinchDistance / initialPinchDistance; | |
viewer.style.transform = `scale(${pinchScale})`; | |
viewer.style.transformOrigin = `${originX}px ${originY}px`; | |
}, { passive: false }); | |
document.addEventListener("touchend", (e) => { | |
if (initialPinchDistance <= 0) { return; } | |
viewer.style.transform = `none`; | |
viewer.style.transformOrigin = `unset`; | |
PDFViewerApplication.pdfViewer.currentScale *= pinchScale; | |
const rect = container.getBoundingClientRect(); | |
const dx = startX - rect.left; | |
const dy = startY - rect.top; | |
container.scrollLeft += dx * (pinchScale - 1); | |
container.scrollTop += dy * (pinchScale - 1); | |
reset(); | |
}); | |
} | |
document.addEventListener('webviewerloaded', () => { | |
if (!pinchZoomEnabled) { | |
pinchZoomEnabled = true; | |
enablePinchZoom(); | |
} | |
}); | |
</script> |
hi guys, if you use modern browser, please upgrade pdfjs to latest version or the supported version(version >=3.3.122, for more info see this PR), pdfjs now support pinch-to-zoom feature
.
if unfortunately, not use modern browser(for example, you have to use pdfjs version v2.x), this code work perfectly!
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Thank you @meghrathod - It's working for BlazorWebView in MAUI Blazor