I have been capturing user signatures using signature pad (https://github.com/szimek/signature_pad/). I need to be able to convert these signatures into a jpeg that retains the image of the signature. I can't get it to work with out the images just being a big black box. I think it has something to do with how the images are rendered.
I used this tutorial to create the signatures (https://www.thewebflash.com/using-signature-pad-with-asp-net-mvc/). I need the signature in a picture format so I can put it on my form. I'm guessing something is going wrong because javascript is needed to render the byte[] correctly, so I'm not converting the raw byte[] to a jpeg correctly in the controller (last part).
Here is my code:
Class:
public class Signature
{
public int ID { get; set; }
[UIHint("SignaturePad")]
public byte[] MySignature { get; set; }
}
public class SignatureDbContext : DbContext
{
public DbSet<Signature> SignatureDatabase { get; set; }
}
UIHint attribute in order to specify that the following SignaturePad.cshtml templates should be used to display the model property in a view.
Views\Shared\DisplayTemplates\SignaturePad.cshtml :
@model byte[]
<div class="signature-pad">
<canvas class="panel panel-default"></canvas>
<button type="button" class="btn btn-default btn-sm btn-clear- canvas">Clear</button>
@Html.HiddenFor(model => model, new { @disabled = "disabled" })
and Views\Shared\EditorTemplates\SignaturePad.cshtml :
@model byte[]
<div class="signature-pad">
<canvas class="panel panel-default"></canvas>
<button type="button" class="btn btn-default btn-sm btn-clear-canvas">Clear</button>
@Html.HiddenFor(model => model, ViewData["htmlAttributes"])
In my css Content\Site.css I have this :
.signature-pad > canvas {
display: block;
width: 300px;
height: 150px;
margin-bottom: 5px;
}
In the scripts folder I have a javascript script to help render the image on the view.
SignaturePadInit.js :
var signaturePadWrappers = document.querySelectorAll('.signature-pad');
[].forEach.call(signaturePadWrappers, function (wrapper) {
var canvas = wrapper.querySelector('canvas');
var clearButton = wrapper.querySelector('.btn-clear-canvas');
var hiddenInput = wrapper.querySelector('input[type="hidden"]');
var signaturePad = new SignaturePad(canvas);
// Read base64 string from hidden input
var base64str = hiddenInput.value;
if (base64str) {
// Draws signature image from data URL
signaturePad.fromDataURL('data:image/png;base64,' + base64str);
}
if (hiddenInput.disabled) {
signaturePad.off();
clearButton.classList.add('hidden');
} else {
signaturePad.onEnd = function () {
// Returns signature image as data URL and set it to hidden input
base64str = signaturePad.toDataURL().split(',')[1];
hiddenInput.value = base64str;
};
clearButton.addEventListener('click', function () {
// Clear the canvas and hidden input
signaturePad.clear();
hiddenInput.value = '';
});
}
});
When I want to see the signature in a view I include this at the buttom or else the signature appears as an empty white box:
@section Scripts {
<script src="~/Scripts/signature_pad.min.js"></script>
<script src="~/Scripts/SignaturePadInit.js"></script>
}
The signature_pad.min.js comes default with the signaturepad library through nuget. I didn't touch it and I don't think it needs to be discussed. I haven't included it because it is extremely long.
Here is my code for converting the byte[] to a jpeg. It converts the byte[] to a jpeg and adds it to a pdf but I have excluded everything but the part that converts to a jpeg. even saving the image locally yeilds a file that is a black block with no signature :
public ActionResult GeneratePDFforSignature(int? id)
{
if (id == null)
{
return new HttpStatusCodeResult(HttpStatusCode.BadRequest);
}
Signature signature = db.SignatureDatabase.Find(id);
Image x = (Bitmap)((new ImageConverter()).ConvertFrom(signature.MySignature));
System.Drawing.Image img = x;
img.Save(Server.MapPath("~/Content/test.jpg"), System.Drawing.Imaging.ImageFormat.Jpeg);
//return View();
return RedirectToAction("Index");
}
I really dont know what to do next to fix this and get the signatures as a jpeg with an actual image in it. I guess I'll keep messing with the SignaturePadInit.js for now. If anyone needs me to post more information to fix this please let me know in the comments.
