yyq_wxapp/pages/tool/sign/signature.wxml

<view class="wrapper">
  <view class="handBtn">
    <image catchtap="selectColorEvent" src="{{ selectColor === 'black' ? '/img/sign/color_black_selected.png' : '/img/sign/color_black.png' }}" class="{{ selectColor === 'black' ? 'color_select' : '' }} black-select" data-color="black"
      data-color-value="#1A1A1A"></image>
    <image catchtap="selectColorEvent" src="{{ selectColor === 'red' ? '/img/sign/color_red_selected.png' : '/img/sign/color_red.png' }}" class="{{ selectColor === 'red' ? 'color_select' : '' }} red-select" data-color="red"
      data-color-value="#ca262a"></image>
    <button catchtap="retDraw" class="delBtn">重写</button>
    <!-- <button catchtap="subCanvas" class="subBtn">完成</button> -->
		<button catchtap="saveCanvasAsImg" class="saveBtn">保存</button>
    <!-- <button catchtap="previewCanvasImg" class="saveBtn">预览</button> -->
    <button catchtap="goBack" class="previewBtn">返回</button>
    <button catchtap="subCanvas" class="subBtn">完成</button>
  </view>
  <view class="handCenter">
    <canvas class="handWriting" disable-scroll="true" bindtouchstart="uploadScaleStart" bindtouchmove="uploadScaleMove"
      bindtouchend="uploadScaleEnd" bindtap="mouseDown" canvas-id="handWriting">
    </canvas>
  </view>
  <view class="handRight" >
    <view class="handTitle"  bindtap="previewSign" >合同预览</view>
  </view>
</view>

<canvas canvas-id="preview"></canvas>