dela/pages/paint.html

{{ define "paint" }}

<canvas class="row border border-secondary" id="drawingCanvas" width="256" height="256"></canvas>
<input class="row border border-secondary" type="color" id="colorPicker" value="#000000" aria-label="Drawing color">

<script>
    const canvas = document.getElementById('drawingCanvas');
    const ctx = canvas.getContext('2d');
    const colorPicker = document.getElementById('colorPicker');
    let drawing = false;

    function startDrawing(x, y) {
        drawing = true;
        ctx.beginPath();
        ctx.moveTo(x, y);
    };

    function draw(x, y){
        if (drawing) {
            ctx.strokeStyle = colorPicker.value;
            ctx.lineWidth = 5;
            ctx.lineTo(x, y);
            ctx.stroke();
        }
    };

    function stopDrawing() {
        drawing = false;
        ctx.closePath();
    };

    function getMousePos(event) {
        const rect = canvas.getBoundingClientRect();
        return {
            x: event.clientX - rect.left,
            y: event.clientY - rect.top
        };
    };

    function getTouchPos(event) {
        const rect = canvas.getBoundingClientRect();
        return {
            x: event.touches[0].clientX - rect.left,
            y: event.touches[0].clientY - rect.top
        };
    };

    // Mouse events
    canvas.addEventListener('mousedown', (e) => {
        const pos = getMousePos(e);
        startDrawing(pos.x, pos.y);
    });

    canvas.addEventListener('mousemove', (e) => {
        const pos = getMousePos(e);
        draw(pos.x, pos.y);
    });

    canvas.addEventListener('mouseup', stopDrawing);
    canvas.addEventListener('mouseleave', stopDrawing);

    // Touch events
    canvas.addEventListener('touchstart', (e) => {
        e.preventDefault(); // Prevent scrolling
        const pos = getTouchPos(e);
        startDrawing(pos.x, pos.y);
    });

    canvas.addEventListener('touchmove', (e) => {
        e.preventDefault(); // Prevent scrolling
        const pos = getTouchPos(e);
        draw(pos.x, pos.y);
    });

    canvas.addEventListener('touchend', stopDrawing);

    // Fills with white
    function clearCanvas() {
        ctx.clearRect(0, 0, canvas.width, canvas.height);
    }

    function isCanvasEmpty() {
        const pixels = new Uint32Array(
            ctx.getImageData(0, 0, canvas.width, canvas.height).data.buffer
        );

        return !pixels.some(color => color !== 0);
    }

    function getCanvasImage() {
        if (!isCanvasEmpty()) {
            return canvas.toDataURL("image/png");
        }

        return null;
    }
</script>

{{ end }}