Show converted mouse coordinates of an element with javascript - javascript

I'd like to show a mouse tooltip like this:
with a coordinate system relative to its image.
Whenever the mouse is hovered over one of the 75x75 cells, the position is displayed in text. I can only show the mouse's raw coordinates, but can't figure out the math to display it like it is in the picture.
I'm open to HTML5 implementations as well.

Here’s how to convert mouse coordinates to cell coordinates and display a tooltip
This math calculates which 75x75 cell your mouse is inside:
var col=parseInt(mouseX/75);
var row=parseInt(mouseY/75);
And here is the math to calculate a tip rectangle in the upper-right of that cell:
var tipX=tipCol*75+75-tipWidth;
var tipY=tipRow*75;
You can use canvas to draw the tip inside the cell at your calculated coordinates:
function tip(x,y){
var tipX=tipCol*75+75-tipWidth;
var tipY=tipRow*75;
ctx.beginPath();
ctx.rect(tipX,tipY,tipWidth,tipHeight);
ctx.fillStyle="ivory";
ctx.fill();
ctx.fillStyle="blue";
ctx.fillText(tipCol+","+tipRow,tipX+2,tipY+17);
}
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/9V5QK/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; padding:25px;}
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var canvasOffset=$("#canvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var startX;
var startY;
var isDown=false;
var tipWidth=35;
var tipHeight=22;
var tipRow;
var tipCol;
ctx.font="14pt verdana";
draw();
function draw(){
// you would just draw your image here
// ctx.drawImage(0,0,image.width,image.height);
// but for illustration, this just recreates your image
ctx.beginPath();
ctx.rect(0,0,375,225);
for(var x=1;x<5;x++){ ctx.moveTo(x*75,0); ctx.lineTo(x*75,canvas.height); }
for(var y=1;y<3;y++){ ctx.moveTo(0,y*75); ctx.lineTo(canvas.width,y*75); }
ctx.fillStyle="black";
ctx.fill();
ctx.strokeStyle="gray";
ctx.lineWidth=2;
ctx.stroke();
}
function tip(x,y){
var tipX=tipCol*75+75-tipWidth;
var tipY=tipRow*75;
ctx.beginPath();
ctx.rect(tipX,tipY,tipWidth,tipHeight);
ctx.fillStyle="ivory";
ctx.fill();
ctx.fillStyle="blue";
ctx.fillText(tipCol+","+tipRow,tipX+2,tipY+17);
}
function handleMouseMove(e){
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
$("#movelog").html("Move: "+ mouseX + " / " + mouseY);
// Put your mousemove stuff here
var col=parseInt(mouseX/75);
var row=parseInt(mouseY/75);
if(!(row==tipRow && col==tipCol)){
tipCol=col;
tipRow=row;
draw();
tip();
}
}
$("#canvas").mousemove(function(e){handleMouseMove(e);});
}); // end $(function(){});
</script>
</head>
<body>
<p>Move mouse over grid to display current cell</p>
<p id="movelog">Move</p>
<canvas id="canvas" width=375 height=225></canvas>
</body>
</html>

Related

HTML5 Canvas: Replace Cursor with Crossing Lines

I'm trying to replace my cursor within the canvas with two perpendicular lines: one horizontal and one vertical. Example here: http://imgur.com/tUBkQn8
I need to do three things
1) Hide the cursor
2) Draw the crossing lines
3) Erase old lines on mouse move and draw new lines based on new mouse location
The following code is a non-performant way of achieving #2 and #3 (it's incredibly slow re-rendering the entire canvas every time the mouse moves):
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
canvas.addEventListener('mousemove', function(evt) {
// clear the canvas
ctx.clearRect(0, 0, xsize, ysize);
// re-draw the base
drawCanvas();
var mousePos = getMousePos(canvas, evt);
// draw vertical line
ctx.beginPath();
ctx.moveTo(mousePos.x,0);
ctx.lineTo(mousePos.x,ysize);
ctx.stroke();
ctx.closePath();
// draw horizontal line
ctx.beginPath();
ctx.moveTo(0,mousePos.y);
ctx.lineTo(xsize,mousePos.y);
ctx.stroke();
ctx.closePath();
}, false);
So my questions:
1) How do I hide the cursor but still display the lines?
2) Is there a way I can just re-render the crossing lines ONLY, rather than the whole canvas every time the mouse moves? Thanks!
Here's one way to create a custom cursor and maintain performance:
Create a second canvas on top of your main drawing canvas.
Hide the system mouse cursor on both the canvases.
Draw/Move your X-cursor and nothing else on the top canvas
Example code and a Demo: http://jsfiddle.net/m1erickson/abokzhn6/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#wrapper{position:relative;}
#canvas,#cursor{position:absolute; cursor:none;}
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("cursor");
var ctx=canvas.getContext("2d");
var $canvas=$("#cursor");
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
$("#cursor").mousemove(function(e){handleMouseMove(e);});
function handleMouseMove(e){
e.preventDefault();
e.stopPropagation();
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.beginPath();
ctx.moveTo(mouseX,mouseY-15);
ctx.lineTo(mouseX,mouseY+15);
ctx.moveTo(mouseX-15,mouseY);
ctx.lineTo(mouseX+15,mouseY);
ctx.stroke();
}
}); // end $(function(){});
</script>
</head>
<body>
<div id='wrapper'>
<canvas id="canvas" width=300 height=300></canvas>
<canvas id="cursor" width=300 height=300></canvas>
</div>
</body>
</html>
Ad 1
I didn't test it but I think that you can hide cursor by changing cursor image in CSS to white 1x1 image.
Ad 2
Use http://kineticjs.com/

Find all black rectangles in canvas

Let's say I have an scanned paper with some black filled rectangles and I want to positionate all of them, getting their coordinates (X and Y) and their dimensions (Width and Height).
Is there any accurate algorithm which does what I need? I'm new to pixel processing with Javascript and Canvas and I need some help. Thanks in advance!
Identifying the x,y,width,height of all black rectangles involves these steps:
Use context.getImageData to get an array of all the r,g,b,a pixel information on the canvas.
Scan the pixel colors to find any one black pixel.
Find the bounding box of the black rectangle containing that one black pixel.
That bounding box will give you the x,y,width,height of one black rectangle.
Clear that black rectangle so that it is not found when searching for the next black rectangle.
Repeat step#1 until all the rectangles are identified.
Here's example code and a Demo: http://jsfiddle.net/m1erickson/3m0dL368/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
#clips{border:1px solid blue; padding:5px;}
img{margin:3px;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var cw,ch;
// background definition
// OPTION: look at the top-left pixel and assume == background
// then set these vars automatically
var isTransparent=false;
var bkColor={r:255,g:255,b:255};
var bkFillColor="rgb("+bkColor.r+","+bkColor.g+","+bkColor.b+")";
cw=canvas.width;
ch=canvas.height;
ctx.fillStyle="white";
ctx.fillRect(0,0,canvas.width,canvas.height);
drawTestRect(30,30,50,50,"1");
drawTestRect(100,30,50,50,"2");
drawTestRect(170,30,50,50,"3");
function drawTestRect(x,y,w,h,label){
ctx.fillStyle="black";
ctx.fillRect(x,y,w,h);
ctx.fillStyle="white";
ctx.font="24px verdana";
ctx.fillText(label,x+10,y+25);
}
function clipBox(data){
var pos=findEdge(data);
if(!pos.valid){return;}
var bb=findBoundary(pos,data);
alert("Found target at "+bb.x+"/"+bb.y+", size: "+bb.width+"/"+bb.height);
clipToImage(bb.x,bb.y,bb.width,bb.height);
if(isTransparent){
// clear the clipped area
// plus a few pixels to clear any anti-aliasing
ctx.clearRect(bb.x-2,bb.y-2,bb.width+4,bb.height+4);
}else{
// fill the clipped area with the bkColor
// plus a few pixels to clear any anti-aliasing
ctx.fillStyle=bkFillColor;
ctx.fillRect(bb.x-2,bb.y-2,bb.width+4,bb.height+4);
}
}
function xyIsInImage(data,x,y){
// find the starting index of the r,g,b,a of pixel x,y
var start=(y*cw+x)*4;
if(isTransparent){
return(data[start+3]>25);
}else{
var r=data[start+0];
var g=data[start+1];
var b=data[start+2];
var a=data[start+3]; // pixel alpha (opacity)
var deltaR=Math.abs(bkColor.r-r);
var deltaG=Math.abs(bkColor.g-g);
var deltaB=Math.abs(bkColor.b-b);
return(!(deltaR<5 && deltaG<5 && deltaB<5 && a>25));
}
}
function findEdge(data){
for(var y=0;y<ch;y++){
for(var x=0;x<cw;x++){
if(xyIsInImage(data,x,y)){
return({x:x,y:y,valid:true});
}
}}
return({x:-100,y:-100,valid:false});
}
function findBoundary(pos,data){
var x0=x1=pos.x;
var y0=y1=pos.y;
while(y1<=ch && xyIsInImage(data,x1,y1)){y1++;}
var x2=x1;
var y2=y1-1;
while(x2<=cw && xyIsInImage(data,x2,y2)){x2++;}
return({x:x0,y:y0,width:x2-x0,height:y2-y0+1});
}
function drawLine(x1,y1,x2,y2){
ctx.beginPath();
ctx.moveTo(x1,y1);
ctx.lineTo(x2,y2);
ctx.strokeStyle="red";
ctx.lineWidth=0.50;
ctx.stroke();
}
function clipToImage(x,y,w,h){
// don't save anti-alias slivers
if(w<3 || h<3){ return; }
// save clipped area to an img element
var tempCanvas=document.createElement("canvas");
var tempCtx=tempCanvas.getContext("2d");
tempCanvas.width=w;
tempCanvas.height=h;
tempCtx.drawImage(canvas,x,y,w,h,0,0,w,h);
var image=new Image();
image.width=w;
image.height=h;
image.src=tempCanvas.toDataURL();
$("#clips").append(image);
}
$("#unbox").click(function(){
var imgData=ctx.getImageData(0,0,cw,ch);
var data=imgData.data;
clipBox(data);
});
}); // end $(function(){});
</script>
</head>
<body>
<button id="unbox">Clip next sub-image</button><br>
<canvas id="canvas" width=300 height=150></canvas><br>
<h4>Below are images clipped from the canvas above.</h4><br>
<div id="clips"></div>
</body>
</html>

Moving canvas shapes with mouse

After pressing a button, I'd like to draw a circle at the tip of the mouse pointer on a canvas and then place it when the user clicks again. Here's what I've got so far:
$("#button").click(function(e){
var canvas = document.getElementById('MyCanvas');
var context = canvas.getContext('2d');
canvas.addEventListener('mousemove', function(evt) {
var mousePos = getMousePos(canvas, evt);
var message = 'Mouse position: ' + mousePos.x + ',' + mousePos.y;
console.log(message);
var nodehandle = document.getElementById('circle');
if(mousePos.x && mousePos.y) {
nodehandle.x = mousePos.x;
nodehandle.y = mousePos.y;
flag = 1;
}
}, false);
});
function getMousePos(canvas, evt) {
var rect = canvas.getBoundingClientRect();
return {
x: evt.clientX - rect.left,
y: evt.clientY - rect.top
};
}
My problem is that when I draw a circle like this:
function drawCircle(mouseX, mouseY){
var c = document.getElementById("grid");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(95,50,5,0,2*Math.PI);
ctx.stroke();
}
I don't know how to select that circle (the getElementById('circle') returns null even if I add ctx.id='circle' to the drawCircle function). I'm also going to need to erase and redraw the circle each time the mouse moves, and I'm sure there's a nice way to do that but I'm not aware of it.
Anything you draw on the canvas--like circles, are just like dried paint on the canvas.
Your circles cannot be selected or moved like html elements.
To move a circle you must clear the canvas and redraw the circle at a different location.
It's convenient to store info about the circle in an object.
var circle1 = { centerX:100, centerY=100, radius=20 }
And you can draw circle1 using that info:
ctx.beginPath();
ctx.arc(circle1.centerX, circle1.centerY, circle1.radius, 0,Math.PI*2);
ctx.closePath();
ctx.fill();
For more than 1 circle you can create a circles array and put each circle object into that array
var circles=[];
circles.push(circle1);
Then to "move" a circle, just change the object's centerX/centerY to the mouse position and redraw all the circles on the canvas.
circle1.centerX=mouseX;
circle1.centerY=mouseY;
// Clear the canvas and redraw all circles
// The "moved" circle will be redrawn at its new position
function drawAll(){
ctx.clearRect(0,0,canvas.width,canvas.height);
for(var i=0;i<circles.length;i++){
var c=circles[i];
ctx.beginPath();
ctx.arc(c.centerX,c.centerY,c.radius,0,Math.PI*2);
ctx.closePath();
ctx.fillStyle=c.color;
ctx.fill();
}
}
You can use Html radio buttons to determine which action a mouse-click will do:
Create a new circle at the mouse position, or
Select the circle under the mouse position, or
"Move" the currently selected circle
Here's example code and a Demo: http://jsfiddle.net/m1erickson/CEB7T/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
// get references to the canvas and its context
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var $canvas=$("#canvas");
// get the canvas position on the page
// used to get mouse position
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var scrollX=$canvas.scrollLeft();
var scrollY=$canvas.scrollTop();
ctx.lineWidth=3;
// save info about each circle in an object
var circles=[];
var selectedCircle=-1;
// the html radio buttons indicating what action to do upon mousedown
var $create=$("#rCreate")[0];
var $select=$("#rSelect")[0];
var $move=$("#rMove")[0];
// draw all circles[]
function drawAll(){
ctx.clearRect(0,0,canvas.width,canvas.height);
for(var i=0;i<circles.length;i++){
var c=circles[i];
ctx.beginPath();
ctx.arc(c.cx,c.cy,c.radius,0,Math.PI*2);
ctx.closePath();
ctx.fillStyle=c.color;
ctx.fill();
// if this is the selected circle, highlight it
if(selectedCircle==i){
ctx.strokeStyle="red";
ctx.stroke();
}
}
}
function handleMouseDown(e){
e.preventDefault();
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
if($create.checked){
// create a new circle a the mouse position and select it
circles.push({cx:mouseX,cy:mouseY,radius:10,color:randomColor()});
selectedCircle=circles.length-1;
}
if($select.checked){
// unselect any selected circle
selectedCircle=-1;
// iterate circles[] and select a circle under the mouse
for(var i=0;i<circles.length;i++){
var c=circles[i];
var dx=mouseX-c.cx;
var dy=mouseY-c.cy;
var rr=c.radius*c.radius;
if(dx*dx+dy*dy<rr){ selectedCircle=i; }
}
}
if($move.checked && selectedCircle>=0){
// move the selected circle to the mouse position
var c=circles[selectedCircle];
c.cx=mouseX;
c.cy=mouseY;
}
// redraw all circles
drawAll();
}
// return a random color
function randomColor(){
return('#'+Math.floor(Math.random()*16777215).toString(16));
}
// handle mousedown events
$("#canvas").mousedown(function(e){handleMouseDown(e);});
}); // end $(function(){});
</script>
</head>
<body>
<input type="radio" name="grp1" id="rCreate" checked>Click will create a new circle.<br>
<input type="radio" name="grp1" id="rSelect">Click will select an existing circle.<br>
<input type="radio" name="grp1" id="rMove">Click will move selected circle.<br>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

Canvas size in HTML5

I have this code in my project, here is the link: http://jsfiddle.net/89wgk/
This is my code:
<canvas id="myCanvas" width="188" height="200"></canvas>
var rectWidth = 110;
var rectHeight = 110;
var rectX = 10;
var rectY = 25;
When I put the mouse in curved rectangle starts the shadow, but I want that to happen when I put the mouse over the reeds (rectangle) and not within the canvas.
I wonder how do I run the shadow so when I move the mouse over the rectangle?
Here is how I would do it:
create a function that draws the arc shape because it must be redrawn often
listen for mouseMove events on the canvas
test whether the mouse is inside the arc with context.isPointInside(mouseX,mouseY)
redraw the arc with/without the shadow based on if the mouse is inside the arc
Have Fun!
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/64BHx/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var context=canvas.getContext("2d");
var $canvas=$("#canvas");
var canvasOffset=$canvas.offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var w = 110;
var h = 110;
var x = 10;
var y = 25;
var isShadowed=false;
context.strokeStyle="#FF2A2A";
context.shadowBlur = 20;
context.shadowOffsetX = 5;
context.shadowOffsetY = 5;
context.globalAlpha=.250;
context.strokeRect(x,y,w,h);
context.globalAlpha=1.00;
function draw(){
// clear the canvas
context.clearRect(0,0,canvas.width,canvas.height);
// save the context state
context.save();
// set/clear the shadow based on isShadowed
context.shadowColor= isShadowed ? '#7FD4FF' : "#FFFFFF";
// draw the arc shape
context.beginPath();
context.moveTo(x,y);
context.quadraticCurveTo(x+w-2,y+2,x+w,y+h);
context.lineTo(x+w-35,y+h);
context.quadraticCurveTo(x+w-2-35,y+2+35,x,y+35);
context.lineTo(x,y);
context.fillStyle="red";
context.fill();
context.stroke();
// restore the context state
context.restore();
}
// testing: display if mouse is in/out of arc shape
var $status=$("#status");
// listen for mousemove events
$("#canvas").mousemove(function(e){handleMouseMove(e);});
// handle mousemove events
function handleMouseMove(e){
// we alone are using mousemove events
e.preventDefault();
// get current mouse X/Y
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
// hit test if mouse is inside the arc shape
var isInside=context.isPointInPath(mouseX,mouseY);
$status.text("Is mouse inside: "+isInside);
// don't redraw unless needed
if(isInside && isShadowed){return;}
if(!isInside && !isShadowed){return;}
// change the shadow and redraw
isShadowed=isInside;
draw();
}
// start by drawing the unshadowed arc
draw();
}); // end $(function(){});
</script>
</head>
<body>
<p id="status">Status</p><br>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

To rotation an image in canvas using mouse

In my code I am loading an image in to a canvas. Then I need to resize, rotate and drag it. I managed to implement both dragging and resizing.
How can I implement rotation(along the center of the image) using mouse on this code.
My HTML page:
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; padding:10px;}
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var canvasOffset=$("#canvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var startX;
var startY;
var isDown=false;
var pi2=Math.PI*2;
var resizerRadius=8;
var rr=resizerRadius*resizerRadius;
var draggingResizer={x:0,y:0};
var imageX=50;
var imageY=50;
var imageWidth,imageHeight,imageRight,imageBottom;
var draggingImage=false;
var startX;
var startY;
var img=new Image();
img.onload=function(){
imageWidth=img.width;
imageHeight=img.height;
imageRight=imageX+imageWidth;
imageBottom=imageY+imageHeight
draw(true,false);
}
img.src="https://dl.dropboxusercontent.com/u/139992952/stackoverflow/facesSmall.png";
function draw(withAnchors,withBorders){
// clear the canvas
ctx.clearRect(0,0,canvas.width,canvas.height);
// draw the image
ctx.drawImage(img,0,0,img.width,img.height,imageX,imageY,imageWidth,imageHeight);
// optionally draw the draggable anchors
if(withAnchors){
drawDragAnchor(imageX,imageY);
drawDragAnchor(imageRight,imageY);
drawDragAnchor(imageRight,imageBottom);
drawDragAnchor(imageX,imageBottom);
}
// optionally draw the connecting anchor lines
if(withBorders){
ctx.beginPath();
ctx.moveTo(imageX,imageY);
ctx.lineTo(imageRight,imageY);
ctx.lineTo(imageRight,imageBottom);
ctx.lineTo(imageX,imageBottom);
ctx.closePath();
ctx.stroke();
}
}
function drawDragAnchor(x,y){
ctx.beginPath();
ctx.arc(x,y,resizerRadius,0,pi2,false);
ctx.closePath();
ctx.fill();
}
function anchorHitTest(x,y){
var dx,dy;
// top-left
dx=x-imageX;
dy=y-imageY;
if(dx*dx+dy*dy<=rr){ return(0); }
// top-right
dx=x-imageRight;
dy=y-imageY;
if(dx*dx+dy*dy<=rr){ return(1); }
// bottom-right
dx=x-imageRight;
dy=y-imageBottom;
if(dx*dx+dy*dy<=rr){ return(2); }
// bottom-left
dx=x-imageX;
dy=y-imageBottom;
if(dx*dx+dy*dy<=rr){ return(3); }
return(-1);
}
function hitImage(x,y){
return(x>imageX && x<imageX+imageWidth && y>imageY && y<imageY+imageHeight);
}
function handleMouseDown(e){
startX=parseInt(e.clientX-offsetX);
startY=parseInt(e.clientY-offsetY);
draggingResizer=anchorHitTest(startX,startY);
draggingImage= draggingResizer<0 && hitImage(startX,startY);
}
function handleMouseUp(e){
draggingResizer=-1;
draggingImage=false;
draw(true,false);
}
function handleMouseOut(e){
handleMouseUp(e);
}
function handleMouseMove(e){
if(draggingResizer>-1){
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
// resize the image
switch(draggingResizer){
case 0: //top-left
imageX=mouseX;
imageWidth=imageRight-mouseX;
imageY=mouseY;
imageHeight=imageBottom-mouseY;
break;
case 1: //top-right
imageY=mouseY;
imageWidth=mouseX-imageX;
imageHeight=imageBottom-mouseY;
break;
case 2: //bottom-right
imageWidth=mouseX-imageX;
imageHeight=mouseY-imageY;
break;
case 3: //bottom-left
imageX=mouseX;
imageWidth=imageRight-mouseX;
imageHeight=mouseY-imageY;
break;
}
// enforce minimum dimensions of 25x25
if(imageWidth<25){imageWidth=25;}
if(imageHeight<25){imageHeight=25;}
// set the image right and bottom
imageRight=imageX+imageWidth;
imageBottom=imageY+imageHeight;
// redraw the image with resizing anchors
draw(true,true);
}else if(draggingImage){
imageClick=false;
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
// move the image by the amount of the latest drag
var dx=mouseX-startX;
var dy=mouseY-startY;
imageX+=dx;
imageY+=dy;
imageRight+=dx;
imageBottom+=dy;
// reset the startXY for next time
startX=mouseX;
startY=mouseY;
// redraw the image with border
draw(false,true);
}
}
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUp(e);});
$("#canvas").mouseout(function(e){handleMouseOut(e);});
}); // end $(function(){});
</script>
</head>
<body>
<p>Resize the image using the 4 draggable corner anchors</p>
<p>You can also drag the image</p>
<canvas id="canvas" width=350 height=350></canvas>
</body>
</html>
Here’s how to use a drag-handle to rotate an image
The mousedown event handler hit-tests if the user is starting to drag the rotation-handle.
This hit-testing is made easier with context.isPointInPath(x,y) which tests whether a specified [x,y] coordinate is inside the most recently drawn path (Conveniently, the rotation-handle is actually a path).
So mousedown activates the drag-handle like this:
Calculate the current mouseX and mouseY.
Redraw the rotation handle (required because isPointInPath hit-tests just the most recent path)
Set the isDown flag if the user did click in the rotation handle.
The mousedown code looks like this:
function handleMouseDown(e){
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
drawRotationHandle(false);
isDown=ctx.isPointInPath(mouseX,mouseY);
}
Yes...we could have simply hit-tested a circle on the end of the rotation-handle, but using isPointInPath will allow you to draw whatever fancy rotation handle you desire.
And isPointInPath has another nice benefit. When the context containing the path is rotated, isPointInPath will hit-test the rotated path for you. This means you don't have to code the math to unrotate the mouse coordinates to do the hit testing--it's done for you!
The mousemove handler redraws the rotatable image at the angle specified by the rotation-handle:
If the isDown flag is not set, just return (the user is not dragging the rotation-handle).
Calculate the current mouseX and mouseY.
Calculate the current angle of the rotation-handle.
Redraw the rotatable image at the current angle.
The mousemove code looks like this:
function handleMouseMove(e){
if(!isDown){return;}
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
var dx=mouseX-cx;
var dy=mouseY-cy;
r=Math.atan2(dy,dx);
draw();
}
The image is drawn at the specified rotation using context's transform methods
function drawRect(){
ctx.save();
ctx.translate(cx,cy);
ctx.rotate(r);
ctx.drawImage(img,0,0);
ctx.restore();
}
Finally, the mouseup and mouseout handlers stop the drag operation by clearing the isDown flag.
function handleMouseUp(e){
isDown=false;
}
function handleMouseOut(e){
isDown=false;
}
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/QqwKR/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
#canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var canvasOffset=$("#canvas").offset();
var offsetX=canvasOffset.left;
var offsetY=canvasOffset.top;
var isDown=false;
var cx=canvas.width/2;
var cy=canvas.height/2;
var w;
var h;
var r=0;
var img=new Image();
img.onload=function(){
w=img.width/2;
h=img.height/2;
draw();
}
img.src="facesSmall.png";
function draw(){
ctx.clearRect(0,0,canvas.width,canvas.height);
drawRotationHandle(true);
drawRect();
}
function drawRect(){
ctx.save();
ctx.translate(cx,cy);
ctx.rotate(r);
ctx.drawImage(img,0,0,img.width,img.height,-w/2,-h/2,w,h);
ctx.restore();
}
function drawRotationHandle(withFill){
ctx.save();
ctx.translate(cx,cy);
ctx.rotate(r);
ctx.beginPath();
ctx.moveTo(0,-1);
ctx.lineTo(w/2+20,-1);
ctx.lineTo(w/2+20,-7);
ctx.lineTo(w/2+30,-7);
ctx.lineTo(w/2+30,7);
ctx.lineTo(w/2+20,7);
ctx.lineTo(w/2+20,1);
ctx.lineTo(0,1);
ctx.closePath();
if(withFill){
ctx.fillStyle="blue";
ctx.fill();
}
ctx.restore();
}
function handleMouseDown(e){
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
drawRotationHandle(false);
isDown=ctx.isPointInPath(mouseX,mouseY);
console.log(isDown);
}
function handleMouseUp(e){
isDown=false;
}
function handleMouseOut(e){
isDown=false;
}
function handleMouseMove(e){
if(!isDown){return;}
mouseX=parseInt(e.clientX-offsetX);
mouseY=parseInt(e.clientY-offsetY);
var dx=mouseX-cx;
var dy=mouseY-cy;
r=Math.atan2(dy,dx);
draw();
}
$("#canvas").mousedown(function(e){handleMouseDown(e);});
$("#canvas").mousemove(function(e){handleMouseMove(e);});
$("#canvas").mouseup(function(e){handleMouseUp(e);});
$("#canvas").mouseout(function(e){handleMouseOut(e);});
}); // end $(function(){});
</script>
</head>
<body>
<p>Rotate by dragging blue rotation handle</p>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

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