javascript - Canvas change size of drawings live -


i'm trying achieve following. have html5 canvas, can draw in. code this:

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 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();                  }              }          }
<html>          <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>

so drawing lines 1 point another.

now i'm wondering following. of should know onenote, has feature can draw something, , see "whoops, drawn big or small in comparison other things have drawn" , can mark , grab corner , make rectangle marked smaller or bigger.

i'm thinking same solution in canvas. people can draw in canvas, , there's resize button, when click on it, can "draw" rectangle (like dotted border , transparet fill) , in rectangle marked. can grab 1 of corners , make marked drawings smaller or bigger, , move content well.

but honestly, have no idea how started that. has idea on how that?

not difficult:

  1. create button, attach event listener, call function. i’ll call resize purpose of guide
  2. create dotted border overlay on canvas. make div, wrap canvas wrapper, apply bit of css. voilà.
  3. attach event handlers div make resizable or search web library can that.
  4. then you’ll have redraw canvas image canvasrenderingcontext2d.drawimage().

it’s worth noting canvases raster-graphics. canvas become unsharp enlarging.


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