Ruby on rails 将JSON呈现为虾PDF格式的图像

我在rails 3.2应用程序中使用了prawn pdf和signature pad gem，但在将JSON数据转换为要在pdf中呈现的图像时遇到了问题

我有一个完成时的签名板，将JSON数据扔到表中，看起来是这样的

JSON

我看到了，但我不确定如何最好地实现它

控制器

  def show
    @form = Form.find(params[:id])

    respond_to do |format|
      format.html
      format.pdf do
          pdf = FormPdf.new(@form)
          send_data pdf.render, filename: "form - #{@form.title}", type: "application/pdf", disposition: "inline"
      end
    end
  end

对虾PDF

# encoding: utf-8
class FormPdf < Prawn::Document

  def initialize(form)
    super()
    @form = form
    all
  end

  def all
    text "Form text here"
    move_down 20
    signature_data = [[@form.signature, "Signature of person"]]
      table(signature_data, position: :center) do 
      cells.style(:border_width => 0)
    end
  end

编码：utf-8 类FormPdf0） 结束 结束 请参见：

有问题的签名图像：

幸运的是，我在我的工作场所也做了类似的事情，所以我将带你经历整个思考过程。假设我们将数据存储在

@sig

中，并设置一个签名框

dimension

：

signature = '[{"lx":29,"ly":18,"mx":29,"my":17},{"lx":29,"ly":19,"mx":29,"my":18},{"lx":29,"ly":24,"mx":29,"my":19},{"lx":29,"ly":27,"mx":29,"my":24},{"lx":29,"ly":30,"mx":29,"my":27},{"lx":29,"ly":32,"mx":29,"my":30},{"lx":32,"ly":32,"mx":29,"my":32},{"lx":33,"ly":32,"mx":32,"my":32},{"lx":35,"ly":31,"mx":33,"my":32},{"lx":39,"ly":24,"mx":35,"my":31},{"lx":42,"ly":16,"mx":39,"my":24},{"lx":48,"ly":7,"mx":42,"my":16},{"lx":51,"ly":2,"mx":48,"my":7},{"lx":54,"ly":-3,"mx":51,"my":2},{"lx":58,"ly":2,"mx":58,"my":1},{"lx":59,"ly":9,"mx":58,"my":2},{"lx":60,"ly":18,"mx":59,"my":9},{"lx":60,"ly":27,"mx":60,"my":18},{"lx":60,"ly":38,"mx":60,"my":27},{"lx":55,"ly":45,"mx":60,"my":38},{"lx":49,"ly":51,"mx":55,"my":45},{"lx":45,"ly":54,"mx":49,"my":51},{"lx":39,"ly":57,"mx":45,"my":54},{"lx":35,"ly":51,"mx":35,"my":50},{"lx":43,"ly":45,"mx":35,"my":51},{"lx":54,"ly":39,"mx":43,"my":45},{"lx":70,"ly":32,"mx":54,"my":39},{"lx":81,"ly":28,"mx":70,"my":32},{"lx":96,"ly":25,"mx":81,"my":28},{"lx":111,"ly":23,"mx":96,"my":25},{"lx":119,"ly":23,"mx":111,"my":23},{"lx":126,"ly":23,"mx":119,"my":23},{"lx":129,"ly":23,"mx":126,"my":23},{"lx":130,"ly":23,"mx":129,"my":23},{"lx":128,"ly":24,"mx":130,"my":23},{"lx":117,"ly":25,"mx":128,"my":24},{"lx":105,"ly":27,"mx":117,"my":25},{"lx":96,"ly":29,"mx":105,"my":27},{"lx":89,"ly":30,"mx":96,"my":29},{"lx":85,"ly":30,"mx":89,"my":30},{"lx":84,"ly":31,"mx":85,"my":30},{"lx":87,"ly":32,"mx":84,"my":31},{"lx":101,"ly":36,"mx":87,"my":32},{"lx":118,"ly":39,"mx":101,"my":36},{"lx":136,"ly":42,"mx":118,"my":39},{"lx":151,"ly":43,"mx":136,"my":42},{"lx":165,"ly":43,"mx":151,"my":43},{"lx":171,"ly":40,"mx":165,"my":43},{"lx":175,"ly":37,"mx":171,"my":40},{"lx":177,"ly":34,"mx":175,"my":37},{"lx":178,"ly":32,"mx":177,"my":34},{"lx":178,"ly":31,"mx":178,"my":32}]'
@sig = JSON.parse signature
sigpad_height = 55
sigpad_width = 198

然后在

光标

点创建一个

边界框

，并从JSON数据中绘制

线

。我们必须使用

边界框

的原因是设置

线

原点的坐标。否则，

行

功能将使用页面左下角作为原点：

bounding_box([0, cursor], width: sigpad_width, height: sigpad_height) do
  stroke_bounds
  @sig.each do |e|
    stroke { line [e["lx"], e["ly"]],
                  [e["mx"], e["my"]] }
  end
end

生成的PDF将是：

请注意图像是如何颠倒的，这是由于

PDF

和

canvas

之间的轴方向点不同造成的。在

PDF

中，原点位于左下角，而在

画布中，原点位于左上角。我们需要做的是将坐标从
canvas
style转换为
PDF
style。一个基本的转换是将其翻转到x轴上，然后将其平移回
sigpad\u height
。
行
代码现在是：

    stroke { line [e["lx"], sigpad_height - e["ly"]],
                  [e["mx"], sigpad_height - e["my"]] }

最终结果将是：


如果不希望在
边界框周围添加边框
将删除
笔划边界
。您需要注意的几个问题：


SignaturePad捕获HTML签名板维度之外的数据坐标，因此您可以看到渲染的PDF签名在其
边界框
之外的线条过多
上述转换假定边界框和HTML填充的签名高度相同。如果不同，则需要添加一些偏移，以便由于翻转x轴而将签名转换回正确位置
取决于如何在数据库中存储JSON。您可能可以通过
：hash
访问坐标。因此
e[“lx”]
将产生
nil
，您必须使用
e[：lx]
您在
FormPDF#initialize
上有一个打字错误：应该是
@form=form
。此外，我建议使用不带空格的文件名，其中包括扩展名。希望这对我们有帮助！非常感谢你。
    stroke { line [e["lx"], sigpad_height - e["ly"]],
                  [e["mx"], sigpad_height - e["my"]] }