wiki-grav/plugins/form/templates/forms/fields/signature/signature.html.twig

{% extends "forms/field.html.twig" %}

{% block prepend %}
    <div id="signature-pad" class="signature-pad">
        <div class="signature-pad--body">
            <canvas></canvas>
        </div>
        <div class="signature-pad--footer">
            <div class="description">Sign above</div>

            <div class="signature-pad--actions">
                <div>
                    <button type="button" class="btn btn-primary-border" data-action="clear">Clear Signature</button>
                </div>
            </div>
        </div>
    </div>

    <script src="{{ url('plugin://form/assets/signature_pad.js') }}"></script>
    <script>

        var wrapper = document.getElementById("signature-pad");
        var clearButton = wrapper.querySelector("[data-action=clear]");

        var canvas = wrapper.querySelector("canvas");
        var signaturePad = new SignaturePad(canvas, {
            // It's Necessary to use an opaque color when saving image as JPEG;
            // this option can be omitted if only saving as PNG or SVG
            backgroundColor: 'rgb(255, 255, 255)',
            onEnd: function() {
                var input = document.querySelector('[name="data[{{ field.name }}]"]');
                input.value = this.toDataURL();
            }
        });

        // Adjust canvas coordinate space taking into account pixel ratio,
        // to make it look crisp on mobile devices.
        // This also causes canvas to be cleared.
        function resizeCanvas() {
            // When zoomed out to less than 100%, for some very strange reason,
            // some browsers report devicePixelRatio as less than 1
            // and only part of the canvas is cleared then.
            var ratio =  Math.max(window.devicePixelRatio || 1, 1);

            // This part causes the canvas to be cleared
            canvas.width = canvas.offsetWidth * ratio;
            canvas.height = canvas.offsetHeight * ratio;
            canvas.getContext("2d").scale(ratio, ratio);

            // This library does not listen for canvas changes, so after the canvas is automatically
            // cleared by the browser, SignaturePad#isEmpty might still return false, even though the
            // canvas looks empty, because the internal data of this library wasn't cleared. To make sure
            // that the state of this library is consistent with visual state of the canvas, you
            // have to clear it manually.
            signaturePad.clear();
        }

        // On mobile devices it might make more sense to listen to orientation change,
        // rather than window resize events.
        window.onresize = resizeCanvas;
        resizeCanvas();

        function download(dataURL, filename) {
            var blob = dataURLToBlob(dataURL);
            var url = window.URL.createObjectURL(blob);

            var a = document.createElement("a");
            a.style = "display: none";
            a.href = url;
            a.download = filename;

            document.body.appendChild(a);
            a.click();

            window.URL.revokeObjectURL(url);
        }

        // One could simply use Canvas#toBlob method instead, but it's just to show
        // that it can be done using result of SignaturePad#toDataURL.
        function dataURLToBlob(dataURL) {
            // Code taken from https://github.com/ebidel/filer.js
            var parts = dataURL.split(';base64,');
            var contentType = parts[0].split(":")[1];
            var raw = window.atob(parts[1]);
            var rawLength = raw.length;
            var uInt8Array = new Uint8Array(rawLength);

            for (var i = 0; i < rawLength; ++i) {
                uInt8Array[i] = raw.charCodeAt(i);
            }

            return new Blob([uInt8Array], { type: contentType });
        }

        clearButton.addEventListener("click", function (event) {
            signaturePad.clear();
        });

    </script>
{% endblock prepend %}

{% block input_attributes %}
    type="hidden"
    {{ parent() }}
{% endblock %}