Utilizing the Vue Signature Pad by neighborhood999 within my Larvel/Vue3 project has been a key feature. However, I am facing an issue crop the signature as users may not utilize the entire available space and might stay towards one side. Researching this problem led me to a GitHub discussion in szimek/signature_pad where multiple users proposed different approaches.

The main challenge I encountered is that all the solutions provided in the post require access to the canvas element of the Signature Pad, which is not exposed by Vue Signature Pad by neighborhood999. I am unsure how to access the canvas element in Vue3. Implementing the code snippets from the post resulted in a common error message:

error canvas.getContext is not a function

, regardless of whether using signaturePad.value or signaturePad. Here's what I have tried so far:

Note: The signature data resides in records, which is an array of signature records, with the actual data contained within records.[0].signature_data. Omitted for clarity are next and prev buttons used for navigation, which I believe are not crucial to the current issue at hand:

<template>
    <div class="container w-[650px] h-[350px] flex flex-col border-2 border-primary-500 p-2 rounded-lg">
        <div class="container overflow-auto">
            <VueSignaturePad width="620px" height="300px" :options="options" :scaleToDevicePixelRatio="true"
                ref="signaturePad" />
        </div>
    </div>

    ...

    <div class="flex flex-row space-x-3 md:justify-start justify-around py-3">
       ...
        <button type="button" class="btn-primary md:w-72 md:flex-none flex-1" @click="saveToFile">Save to file</button>
    </div>
</template>

<script setup>
import { ref, onMounted, onUnmounted, computed, watch } from 'vue';
import { VueSignaturePad } from 'vue-signature-pad';
import useSignatureOps from '@/Composables/useSignatureOps';
import axios from 'axios';

// const devStore = useDeveloperStore();
const { convertLegacySignature, StringToArray } = useSignatureOps;

const props = defineProps({
    records: Array,
})

const options = ref({
    minWidth: 0.5,
    maxWidth: 2.5,
    penColor: 'black',
    backgroundColor: 'white',
});

const saveSignatureForm = useForm({
    url: null,
    signature_id: null,
})

const signaturePad = ref(null);

const currentIndex = ref(0);
const currentSignature = ref(props.records[currentIndex.value]);

....

const saveToFile = () => {
    const { isEmpty, data } = signaturePad.value.saveSignature();
    
    // without cropping the data object returned is perfect with the signature as in the signature pad

    if (!isEmpty) {
        // i want to crop the signature here and download the png to the user...
        // this below line is throwing an exception canvas.getContext is not a function
        const cropped = getCroppedCanvasImage(signaturePad.value); 
        console.log(cropped);
        
        // this below line is another implementation i found also throwing an exception canvas.getContext is not a function
        const cropped = getCroppedCanvasImage(signaturePad.value); 
        console.log(cropped);
    } else {
        console.warn('Warning: Signature is empty.');
    }

}

function getCroppedCanvasImage(canvas) { // here how do I pass the canvas object??

    let originalCtx = canvas.getContext('2d');

    let originalWidth = canvas.width;
    let originalHeight = canvas.height;
    let imageData = originalCtx.getImageData(0, 0, originalWidth, originalHeight);

    let minX = originalWidth + 1, maxX = -1, minY = originalHeight + 1, maxY = -1, x = 0, y = 0, currentPixelColorValueIndex;

    for (y = 0; y < originalHeight; y++) {
        for (x = 0; x < originalWidth; x++) {
            currentPixelColorValueIndex = (y * originalWidth + x) * 4;
            let currentPixelAlphaValue = imageData.data[currentPixelColorValueIndex + 3];
            if (currentPixelAlphaValue > 0) {
                if (minX > x) minX = x;
                if (maxX < x) maxX = x;
                if (minY > y) minY = y;
                if (maxY < y) maxY = y;
            }
        }
    }

    let croppedWidth = maxX - minX;
    let croppedHeight = maxY - minY;
    if (croppedWidth < 0 || croppedHeight < 0) return null;
    let cuttedImageData = originalCtx.getImageData(minX, minY, croppedWidth, croppedHeight);

    let croppedCanvas = document.createElement('canvas'),
        croppedCtx = croppedCanvas.getContext('2d');

    croppedCanvas.width = croppedWidth;
    croppedCanvas.height = croppedHeight;
    croppedCtx.putImageData(cuttedImageData, 0, 0);

    return croppedCanvas.toDataURL();
}

const cropSignatureCanvas = (canvas) => {

    // First duplicate the canvas to not alter the original
    var croppedCanvas = document.createElement('canvas'),
        croppedCtx = croppedCanvas.getContext('2d');

    croppedCanvas.width = canvas.width;
    croppedCanvas.height = canvas.height;
    croppedCtx.drawImage(canvas, 0, 0);

    // Next do the actual cropping
    var w = croppedCanvas.width,
        h = croppedCanvas.height,
        pix = { x: [], y: [] },
        imageData = croppedCtx.getImageData(0, 0, croppedCanvas.width, croppedCanvas.height),
        x, y, index;

    for (y = 0; y < h; y++) {
        for (x = 0; x < w; x++) {
            index = (y * w + x) * 4;
            if (imageData.data[index + 3] > 0) {
                pix.x.push(x);
                pix.y.push(y);

            }
        }
    }
    pix.x.sort(function (a, b) { return a - b });
    pix.y.sort(function (a, b) { return a - b });
    var n = pix.x.length - 1;

    w = pix.x[n] - pix.x[0];
    h = pix.y[n] - pix.y[0];
    var cut = croppedCtx.getImageData(pix.x[0], pix.y[0], w, h);

    croppedCanvas.width = w;
    croppedCanvas.height = h;
    croppedCtx.putImageData(cut, 0, 0);

    return croppedCanvas.toDataURL();
}

</script>