我正在尝试使用 html、javascript 和 canvas 制作一个移动应用程序，基本上向下滚动会增加图像的缩放，向上滚动会减少图像的缩放，但我只能减少缩放，因为向上滚动时不断增加尺寸，我希望它减小尺寸。
部分javascript代码：
1
1134document.addEventListener('touchmove', (event)=>{
if (event.pageY < 0) {
zoomLevel /= 1.1; // zoom out by 10%
} else if (event.pageY > 0) {
zoomLevel *= 1.1; // zoom in by 10%
}
if (zoomLevel < 1) {
zoomLevel = 1;
} else if (zoomLevel > 5) {
zoomLevel = 5;
}
drawImage();
})
function drawImage() {
ctx.clearRect(0, 0, canvasWidth, canvasHeight);
// draw zoom area
const imgWidth = img.width * zoomLevel;
const imgHeight = img.height * zoomLevel;
const imgX = canvasWidth / 2 - imgWidth / 2;
const imgY = canvasHeight / 2 - imgHeight / 2;
ctx.drawImage(img, imgX, imgY, imgWidth, imgHeight);
} 
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要获取
Delta Y，请使用以下代码来解决它，该代码存储触摸位置。let zoomLevel = 1; document.addEventListener('touchstart', (event) => { y = event.touches[0].clientY; }); document.addEventListener('touchmove', (event) => { const deltaY = event.touches[0].clientY - y; y = event.touches[0].clientY; zoomLevel = Math.min(5, Math.max(1, zoomLevel + deltaY * 0.01)); drawImage(); });