https://developers.weixin.qq.com/miniprogram/dev/api/canvas/Canvas.html

iphone15promax不能画出连续的线，只能一段一段的。

iphone13 可以画出连续的线。

代码如下：

//wxml
<canvas canvas-id="signCanvas" class="canvasStyle" 
    bindtouchstart="onTouchStart" 
    bindtouchmove="onTouchMove" 
    bindtouchend="onTouchEnd"></canvas>

//script
Page({
    startX: 0, // Starting X coordinate
    startY: 0, // Starting Y coordinate
    isDrawing: false, // Flag to check if drawing is happening
    ctx: null, // Canvas context


    onLoad: function() {
        this.ctx = wx.createCanvasContext('signCanvas', this);
    },


    onTouchStart: function(e) {
        this.isDrawing = true;
        this.startX = e.touches[0].x;
        this.startY = e.touches[0].y;
    },


    onTouchMove: function(e) {
        if (!this.isDrawing) return;


        let x = e.touches[0].x;
        let y = e.touches[0].y;


        this.ctx.moveTo(this.startX, this.startY);
        this.ctx.lineTo(x, y);
        this.ctx.stroke();


        this.startX = x;
        this.startY = y;


        this.ctx.draw(true); // Add true to keep drawing on the same canvas without clearing previous content
    },


    onTouchEnd: function(e) {
        this.isDrawing = false;
    },


    clearCanvas: function() {
        this.ctx.clearRect(0, 0, 300, 200);
        this.ctx.draw();
    },


    saveCanvas: function() {
        wx.canvasToTempFilePath({
            canvasId: 'signCanvas',
            success: function(res) {
                // res.tempFilePath is the temporary file path of the canvas image
                console.log(res.tempFilePath);
                // You can save this path or upload the image as needed
            }
        }, this);
    }
});

//css
.canvasStyle {
    border: 1px solid #000; /* Basic border for visibility */
    width: 300px; /* Width of the canvas */
    height: 200px; /* Height of the canvas */
}