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draw line snap to grid

Discussion in 'JavaScript' started by money4leads, Jan 21, 2018.

0
  1. #1
    hello
    I am trying to create a page that allow the visitor to draw lines, I have this script but I need the drawing lines to be straight lines and start and end mouse should snap to grid, the grid lines should be visible.
    also, can I add the arc drawing option (can be drawn buy clicking on three points)
    here is my page code:
    <html>
    <script type="text/javascript">
    var canvas, ctx, flag = false,
        prevX = 0,
        currX = 0,
        prevY = 0,
        currY = 0,
        dot_flag = false;

    var x = "black",
        y = 2;

    function init() {
        canvas = document.getElementById('can');
        ctx = canvas.getContext("2d");
        w = canvas.width;
        h = canvas.height;

        canvas.addEventListener("mousemove", function (e) {
            findxy('move', e)
        }, false);
        canvas.addEventListener("mousedown", function (e) {
            findxy('down', e)
        }, false);
        canvas.addEventListener("mouseup", function (e) {
            findxy('up', e)
        }, false);
        canvas.addEventListener("mouseout", function (e) {
            findxy('out', e)
        }, false);
    }

    function color(obj) {
        switch (obj.id) {
            case "green":
                x = "green";
                break;
            case "blue":
                x = "blue";
                break;
            case "red":
                x = "red";
                break;
            case "yellow":
                x = "yellow";
                break;
            case "orange":
                x = "orange";
                break;
            case "black":
                x = "black";
                break;
            case "white":
                x = "white";
                break;
        }
        if (x == "white") y = 14;
        else y = 2;

    }

    function draw() {
        ctx.beginPath();
        ctx.moveTo(prevX, prevY);
        ctx.lineTo(currX, currY);
        ctx.strokeStyle = x;
        ctx.lineWidth = y;
        ctx.stroke();
        ctx.closePath();
    }

    function erase() {
        var m = confirm("Want to clear");
        if (m) {
            ctx.clearRect(0, 0, w, h);
            document.getElementById("canvasimg").style.display = "none";
        }
    }

    function save() {
        document.getElementById("canvasimg").style.border = "2px solid";
        var dataURL = canvas.toDataURL();
        document.getElementById("canvasimg").src = dataURL;
        document.getElementById("canvasimg").style.display = "inline";
    }

    function findxy(res, e) {
        if (res == 'down') {
            prevX = currX;
            prevY = currY;
            currX = e.clientX - canvas.offsetLeft;
            currY = e.clientY - canvas.offsetTop;

            flag = true;
            dot_flag = true;
            if (dot_flag) {
                ctx.beginPath();
                ctx.fillStyle = x;
                ctx.fillRect(currX, currY, 2, 2);
                ctx.closePath();
                dot_flag = false;
            }
        }
        if (res == 'up' || res == "out") {
            flag = false;
        }
        if (res == 'move') {
            if (flag) {
                prevX = currX;
                prevY = currY;
                currX = e.clientX - canvas.offsetLeft;
                currY = e.clientY - canvas.offsetTop;
                draw();
            }
        }
    }
    </script>
    <body onload="init()">
        <canvas id="can" width="400" height="400" style="position:absolute;top:10%;left:10%;border:2px solid;"></canvas>
        <div style="position:absolute;top:12%;left:43%;">Choose Color</div>
        <div style="position:absolute;top:15%;left:45%;width:10px;height:10px;background:green;" id="green" onclick="color(this)"></div>
        <div style="position:absolute;top:15%;left:46%;width:10px;height:10px;background:blue;" id="blue" onclick="color(this)"></div>
        <div style="position:absolute;top:15%;left:47%;width:10px;height:10px;background:red;" id="red" onclick="color(this)"></div>
        <div style="position:absolute;top:17%;left:45%;width:10px;height:10px;background:yellow;" id="yellow" onclick="color(this)"></div>
        <div style="position:absolute;top:17%;left:46%;width:10px;height:10px;background:orange;" id="orange" onclick="color(this)"></div>
        <div style="position:absolute;top:17%;left:47%;width:10px;height:10px;background:black;" id="black" onclick="color(this)"></div>
        <div style="position:absolute;top:20%;left:43%;">Eraser</div>
        <div style="position:absolute;top:22%;left:45%;width:15px;height:15px;background:white;border:2px solid;" id="white" onclick="color(this)"></div>
        <img id="canvasimg" style="position:absolute;top:10%;left:52%;" style="display:none;">
        <input type="button" value="save" id="btn" size="30" onclick="save()" style="position:absolute;top:55%;left:10%;">
        <input type="button" value="clear" id="clr" size="23" onclick="erase()" style="position:absolute;top:55%;left:15%;">
    </body>
    </html>
    Code (markup):

     
    money4leads, Jan 21, 2018 IP
  2. deathshadow

    deathshadow Acclaimed Member

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    #2
    The math for snap to grid -- at least assuming integer precision -- is pretty simple:

    gridX = Math.round( mouseX / gridSize ) * gridSize;

    Now that said, you've got a LOT of problems in your code, static scripting only nonsense in the markup, static style in the markup wasting bandwidth, DIV doing BUTTON's job, wasting time repeatedly grabbing the same element by ID introducing pointless overhead, use of onevent attributes like onclick that we've been told for a decade to stop using (and don't even EXIST if you deploy under the CSP), adding pointless overhead through using single callbacks to handle multiple possibilities...

    Or even that since you aren't recording what's being drawn everything is erased and lost on a window resize.
     
    deathshadow, Feb 3, 2018 IP