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const zoomStepRatio = 0.25,
positive = 1,
negative = -1;
function toLocalCoords(svg, x, y) {
const clientP = new DOMPoint(x, y);
return clientP.matrixTransform(svg.getScreenCTM().inverse());
}
function zoomIn(deltaY) {
return deltaY < 0;
}
function calcSizeChangeAmounts(width, height) {
return {
width: width * zoomStepRatio,
height: height * zoomStepRatio
};
}
function calcValChangeRatios(focusPoint, x, y, width, height) {
return {
x: (focusPoint.x - x) / width,
y: (focusPoint.y - y) / height,
width: (width + x - focusPoint.x) / width,
height: (height + y - focusPoint.y) / height
};
}
function calcValChangeAmounts(focusPoint, x, y, width, height) {
const changeAmount = calcSizeChangeAmounts(width, height),
valChangeRatio = calcValChangeRatios(focusPoint, x, y, width, height);
return {
x: valChangeRatio.x * changeAmount.width,
y: valChangeRatio.y * changeAmount.height,
width: valChangeRatio.width * changeAmount.width,
height: valChangeRatio.height * changeAmount.height
};
}
export default function (svg, e) {
const pointerPosition = toLocalCoords(svg, e.clientX, e.clientY),
sign = zoomIn(e.deltaY) ? positive : negative,
{ x, y, width, height } = svg.viewBox.baseVal,
changeAmount = calcValChangeAmounts(pointerPosition, x, y, width, height),
attr = {
x: x + sign * changeAmount.x,
y: y + sign * changeAmount.y,
width: width + sign * (-changeAmount.x - changeAmount.width),
height: height + sign * (-changeAmount.y - changeAmount.height)
};
return `${attr.x} ${attr.y} ${attr.width} ${attr.height}`;
}
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