【报Bug】canvas canvasToTempFilePath方法高度受限！！！

操作步骤：

<template>  
    <view class="page">  
        <view>canvas:</view>  
        <canvas canvas-id="cnavas" style="width: 300px;":style="'height:' + height + 'px'"></canvas>  
        <view>图片：</view>  
        <image :src="path" mode="widthFix"></image>  
    </view>  
</template>

export default {  
    data: () => ({  
        path: '',  
        height: 320  
    }),  

    created() {},  
    mounted() {  
        var context = uni.createCanvasContext('cnavas');  
        context.setStrokeStyle('#00ff00');  
        context.setLineWidth(5);  
        context.rect(0, 0, 200, this.height-10);  
        context.stroke();  
        context.setStrokeStyle('#ff0000');  
        context.setLineWidth(2);  
        context.moveTo(160, 100);  
        context.arc(100, 100, 60, 0, 2 * Math.PI, true);  
        context.moveTo(140, 100);  
        context.arc(100, 100, 40, 0, Math.PI, false);  
        context.moveTo(85, 80);  
        context.arc(80, 80, 5, 0, 2 * Math.PI, true);  
        context.moveTo(125, 80);  
        context.arc(120, 80, 5, 0, 2 * Math.PI, true);  
        context.stroke();  
        context.draw();  
        setTimeout(this.canvasToTempFilePath, 300)  
    },  
    methods: {  
        canvasToTempFilePath() {  
            uni.canvasToTempFilePath({  
              x: 0,  
              y: 0,  
              width: 300,  
              height: this.height,  
              canvasId: 'cnavas',  
              success: (res) => {  
                this.path = res.tempFilePath  
              }   
            })  
        }  
    }  
};

预期结果：

生成完整的图片

实际结果：

无法生成完整图片