Develop Reference

Pan Zoom behaviour using EaselJS

I’m having some trouble incorporating pan/zoom behaviour with the ability to also drag-move some shapes around on the canvas, using EaselJS.
I want to be able to move the shape ONLY if I mousedown on it, but if I mousedown on the stage (i.e. not on a shape), then I want to be able to pan the stage.
This behaviour needs to be consistent regardless of the ‘zoom’ level (which is altered by the mousewheel).
I have read this: How to stop the event bubble in easljs? Which suggests that the stage mousedown events will fire regardless of whether I have clicked on a shape or empty space, so it would be better to create a ‘background’ shape to capture my mousedown events that are not on a ‘proper’ shape.
This fiddle is how I have set it up: https://jsfiddle.net/hmcleay/mzheuLbg/
var stage = new createjs.Stage("myCanvas");
console.log('stage.scaleX: ', stage.scaleX);
console.log('stage.scaleY: ', stage.scaleY);
function addCircle(r,x,y){
var g=new createjs.Graphics().beginFill("#ff0000").drawCircle(0,0,r);
var s=new createjs.Shape(g)
s.x=x;
s.y=y;
s.on('pressmove', function(ev) {
var localpos = stage.globalToLocal(ev.stageX, ev.stageY)
s.x = localpos.x;
s.y = localpos.y;
stage.update();
});
stage.addChild(s);
stage.update();
}
// create a rectangle 'background' Shape object to cover the stage (to allow for capturing mouse drags on anything except other shapes).
bg = new createjs.Shape();
bg.graphics.beginFill("LightGray").drawRect(10, 10, stage.canvas.width - 20, stage.canvas.height - 20); //deliberately smaller for debugging purposes (easier to see if it moves).
bg.x = 0;
bg.y = 0;
stage.addChild(bg);
stage.update();
//create a rectangle frame to represent the position of the stage.
stageborder = new createjs.Shape();
stageborder.graphics.beginStroke("Black").drawRect(0, 0, stage.canvas.width, stage.canvas.height);
stageborder.x = 0;
stageborder.y = 0;
stage.addChild(stageborder);
stage.update();
// MOUSEWHEEL ZOOM LISTENER - anywhere on canvas.
var factor
canvas.addEventListener("wheel", function(e){
if(Math.max(-1, Math.min(1, (e.wheelDelta || -e.detail)))>0){
factor = 1.1;
} else {
factor = 1/1.1;
}
var local = stage.globalToLocal(stage.mouseX, stage.mouseY);
stage.regX=local.x;
stage.regY=local.y;
stage.x=stage.mouseX;
stage.y=stage.mouseY;
stage.scaleX = stage.scaleX * factor;
stage.scaleY = stage.scaleY * factor;
//re-size the 'background' shape to be the same as the canvas size.
bg.graphics.command.w = bg.graphics.command.w / factor;
bg.graphics.command.h = bg.graphics.command.h / factor;
// re-position the 'background' shape to it's original position of (0,0) in the global space.
var localzero = stage.globalToLocal(0, 0);
bg.x = localzero.x;
bg.y = localzero.y;
stage.update();
});
// listener to add circles to the canvas.
canvas.addEventListener('dblclick', function(){
var localpos = stage.globalToLocal(stage.mouseX, stage.mouseY);
addCircle(10, localpos.x, localpos.y);
});
bg.addEventListener("mousedown", function(ev1){
// purpose of this listener is to be able to capture drag events on the 'background' to pan the whole stage.
// it needs to be a separate 'shape' object (rather than the stage itself), so that it doesn't fire when other shape objects are drag-moved around on the stage.
// get the initial positions of the stage, background, and mousedown.
var mousedownPos0 = {'x': ev1.stageX, 'y': ev1.stageY};
var stagePos0 = {'x': stage.x, 'y': stage.y};
var bgPos0 = {'x': bg.x, 'y': bg.y};
bg.addEventListener('pressmove', function(ev2){
//logic is to pan the stage, which will automatically pan all of it's children (shapes).
// except we want the 'background' shape to stay where it is, so we need to offset it in the opposite direction to the stage movement so that it stays where it is.
stageDelta = {'x': ev2.stageX - mousedownPos0.x, 'y': ev2.stageY - mousedownPos0.y};
//adjust the stage position
stage.x = stagePos0.x + stageDelta.x;
stage.y = stagePos0.y + stageDelta.y;
// return the 'background' shape to global(0,0), so that it doesn't move with the stage.
var localzero = stage.globalToLocal(0,0);
bg.x = localzero.x;
bg.y = localzero.y;
stage.update();
});
});
The grey box is my background shape. I have deliberately made it slightly smaller than the canvas, so that I can see where it is (useful for debugging).
Double click anywhere on the canvas to add some red circles.
If you drag a circle, it only moves that circle.
If you drag on the grey ‘background’ area in between circles, it moves the whole stage (and therefore all the child shapes belonging to the stage).
Because the grey background is also a child of the stage, it wants to move with it. So I have included some code to always return that grey box back to where it started.
The black border represents the position of the ‘stage’, I just added it to help visualise where the stage is.
The mousewheel zoom control is based on the answer to this question: EaselJS - broken panning on zoomed image
Similar to drag-panning, when zooming I have to adjust the size and position of the grey ‘background’ box so that it renders in the same position on the canvas.
However, it doesn’t stay exactly where I want it to… it seems to creep up towards the top left corner of the canvas when I zoom out.
I’ve spent quite some time trying to diagnose this behaviour and can’t find out why it’s happening. I suspect it may have something to do with rounding.. but I’m really not sure.
Can anyone explain why my grey box isn't staying stationary when I zoom in and out?
An alternative method would be to scrap the ‘background’ shape used for capturing mousedown events that aren’t on a ‘proper’ shape.
Instead, it might be possible to use the ‘stage’ mousedown event, but prevent it from moving the stage if the mouse is over a ‘shape’.
Would this be a better way of handling this behaviour? Any suggestions how to prevent it from moving the stage?
Thanks in advance,
Hugh.

Ok,
So as usually happens, after finally asking for help, I managed to work out the problem.
The issue was caused by making the background shape (grey rectangle) 10px smaller than the canvas, so that I could see its position more clearly (to assist with debugging). How ironic that this offset was causing the issue.
The 10px offset was not being converted into the 'local' space when the zoom was applied.
By making the grey rectangle's graphic position at (0,0) with width and height equal to that of the canvas, the problem went away!
Hope this is of use to someone at some point in time.
Cheers,
Hugh.

How do I translate mouse movement distances to SVG coordinate space?

I have an SVG visualization of the distribution of CSS4 color keywords in HSL space here: https://meyerweb.com/eric/css/colors/hsl-dist.html
I recently added zooming via the mouse wheel, and panning via mouse clack-and-drag. I’m able to convert a point from screen space to SVG coordinate space using matrixTransform, .getScreenCTM(), and .inverse() thanks to example code I found online, but how do I convert mouse movements during dragging? Right now I’m just shifting the viewBox coordinates by the X and Y values from event, which means the image drag is faster than the mouse movement when zoomed in.
As an example, suppose I’m zoomed in on the image and am dragging to pan, and I jerk the mouse leftwards and slightly downwards. event.movementX returns -37 and event.movementY returns 6. How do I determine how far that equates to in SVG coordinates, so that the viewBox coordinates are shifted properly?
(Note: I’m aware that there are libraries for this sort of thing, but I’m intentionally writing vanilla JS code in order to learn more about both SVG and JS. So please, don’t post “lol just use library X” and leave it at that. Thanks!)
Edited to add: I was asked to post code. Posting the entire JS seems overlong, but this is the function that fires on mousemove events:
function dragger(event) {
var target = document.getElementById('color-wheel');
var coords = parseViewBox(target);
coords.x -= event.movementX;
coords.y -= event.movementY;
changeViewBox(target,coords);
}
If more is needed, then view source on the linked page; all the JS is at the top of the page. Nothing is external except for a file that just contains all the HSL values and color names for the visualization.

My recommendation:
Don't worry about the movementX/Y properties on the event.
Just worry about where the mouse started and where it is now.
(This has the additional benefit that you get the same result even if you miss some events: maybe because the mouse moved out of the window, or maybe because you want to group events so you only run the code once per animation frame.)
For where the mouse started, you measure that on the mousedown event.
Convert it to a position in the SVG coordinates, using the method you were using,
with .getScreenCTM().inverse() and .matrixTransform().
After this conversion, you don't care where on the screen this point is. You only care about where it is in the picture. That's the point in the picture that you're always going to move to be underneath the mouse.
On the mousemove events, you use that same conversion method to find out where the mouse currently is within the current SVG coordinate system. Then you figure out how far that is from the point (again, in SVG coordinates) that you want underneath the mouse. That's the amount that you use to transform the graphic. I've followed your example and am doing the transform by shifting the x and y parts of the viewBox:
function move(e) {
var targetPoint = svgCoords(event, svg);
shiftViewBox(anchorPoint.x - targetPoint.x,
anchorPoint.y - targetPoint.y);
}
You can also shift the graphic around with a transform on a group (<g> element) within the SVG; just be sure to use that same group element for the getScreenCTM() call that converts from the clientX/Y event coordinates.
Full demo for the drag to pan. I've skipped all your drawing code and the zooming effect.
But the zoom should still work, because the only position you're saving in global values is already converted into SVG coordinates.
var svg = document.querySelector("svg");
var anchorPoint;
function shiftViewBox(deltaX, deltaY) {
svg.viewBox.baseVal.x += deltaX;
svg.viewBox.baseVal.y += deltaY;
}
function svgCoords(event,elem) {
var ctm = elem.getScreenCTM();
var pt = svg.createSVGPoint();
// Note: rest of method could work with another element,
// if you don't want to listen to drags on the entire svg.
// But createSVGPoint only exists on <svg> elements.
pt.x = event.clientX;
pt.y = event.clientY;
return pt.matrixTransform(ctm.inverse());
}
svg.addEventListener("mousedown", function(e) {
anchorPoint = svgCoords(event, svg);
window.addEventListener("mousemove", move);
window.addEventListener("mouseup", cancelMove);
});
function cancelMove(e) {
window.removeEventListener("mousemove", move);
window.removeEventListener("mouseup", cancelMove);
anchorPoint = undefined;
}
function move(e) {
var targetPoint = svgCoords(event, svg);
shiftViewBox(anchorPoint.x - targetPoint.x,
anchorPoint.y - targetPoint.y);
}
body {
display: grid;
margin: 0;
min-height: 100vh;
}
svg {
margin: auto;
width: 70vmin;
height: 70vmin;
border: thin solid gray;
cursor: move;
}
<svg viewBox="-40 -40 80 80">
<polygon fill="skyBlue"
points="0 -40, 40 0, 0 40 -40 0" />
</svg>

So the script needs something so that the vectors moved by the SVG are coordinated against the vectors moved by the mouse on screen. Despite the event being on your target, your SVG, the MouseEvent properties relate to your screen alone.
The movementX read-only property of the MouseEvent interface provides the difference in the X coordinate of the mouse pointer between the given event and the previous mousemove event. In other words, the value of the property is computed like this: currentEvent.movementX = currentEvent.screenX - previousEvent.screenX.
From https://developer.mozilla.org/en-US/docs/Web/API/MouseEvent/movementX
The screenX read-only property of the MouseEvent interface provides the horizontal coordinate (offset) of the mouse pointer in global (screen) coordinates.
So what you're measuring, and to the best of my knowledge the only thing you can measure direcly without additional libraries or complication, is the movement of the pointer in pixel terms across the screen. The only way to make this work in terms of vector for movement of your SVG is to translate the on screen movement to the dimensions that are relevant to your scaled SVG.
My initial thinking was that you would be able to work out the scaling of the SVG object, using some combination of its viewbox and its actual width on the screen. Naturally what would initially appear sensible is not. This approach won't work, if it appears to it would be purely by chance.
But it turns out that the solution is essentially to use the same type of code you've used in your scaling when you approach your mouse movements. The .getScreenCTM() and .inverse() functions are exactly what you'll need again. But instead of trying to find a single point on the SVG to work from, you need to find out what the on-screen distance translates to in the SVG by comparing two points on the SVG instead.
What I provide here isn't necessarily the most optimal solution but hopefully helps explain and gives you something to work further from...
function dragger(event) {
var target = document.getElementById('color-wheel');
var coords = parseViewBox(target);
//Get an initial point in the SVG to start measuring from
var start_pt = target.createSVGPoint();
start_pt.x = 0;
start_pt.y = 0;
var svgcoord = start_pt.matrixTransform(target.getScreenCTM().inverse());
//Create a point within the same SVG that is equivalent to
//the px movement by the pointer
var comparison_pt = target.createSVGPoint();
comparison_pt.x = event.movementX;
comparison_pt.y = event.movementY;
var svgcoord_plus_movement = comparison_pt.matrixTransform(target.getScreenCTM().inverse());
//Use the two SVG points created from screen position values to determine
//the in-SVG distance to change coordinates
coords.x -= (svgcoord_plus_movement.x - svgcoord.x);
//Repeat the above, but for the Y axis
coords.y -= (svgcoord_plus_movement.y - svgcoord.y);
//Deliver the changes to the SVG to update the view
changeViewBox(target,coords);
}
Sorry for the long winded answer, but hopefully it explains it from the beginning enough that anyone else looking to find an answer can get the whole picture if they've not come as far as you have in this script.

From MouseEvent, we have clientX and movememntX. Taken together, we can deduce our last location. We can then take the transform of our current location and subtract it from the transform of our last location:
element.onpointermove = e => {
const { clientX, clientY, movementX, movementY } = e;
const DOM_pt = svg.createSVGPoint();
DOM_pt.x = clientX;
DOM_pt.y = clientY;
const { x, y } = DOM_pt.matrixTransform(svgs[i].getScreenCTM().inverse());
DOM_pt.x += movementX;
DOM_pt.y += movementY;
const { x: last_x, y: last_y } = DOM_pt.matrixTransform(svgs[i].getScreenCTM().inverse());
const dx = last_x - x;
const dy = last_y - y;
// TODO: use dx & dy
}

Draggable element make it snap to the vertices around it with a high snapTolerance

I just wanted to make a grid with a dragged element and make it snap to the vertices around the element I'm dragging. Happens that if the snapTolerance is too high (grid size i.e: 20px) but the asset is not divisible by 20 in size... it won't snap to the next vertex but it will make a 20px jump to the next block. I don't know if I'm being clear but here's a jsfiddle that might help you understand this better.
In this example, I would like the right side to touch the next vertex before the next-block-jump. Is that possible with jQuery UI right now?
I can decrease the snapTolerance but the snappy effect won't be that smooth since the dragged elements may vary in sizes.
I would like to make it stuck on the vertices at all times but have the edges of the dragged element to snap on every vertex around.
$(".draggable-block").draggable({
snapTolerance: 20,
snap: '.guide-line'
});

Try using this option instead of snap:
$(".draggable-block").draggable({
//snapTolerance: 20,
//snap: '.guide-line',
//snapMode: "inner",
grid: [ 5, 5 ]
});
http://api.jqueryui.com/draggable/#option-grid
It looks like the JQuery UI draggable only snaps with its top left corner and always aligns with the lines at that spot.
You could try to do something on the drag event and see if there is anything helpful on the ui parameter:
http://api.jqueryui.com/draggable/#event-drag
Are you required to use a 20px grid? If not, you could define your grid lines based off the width or height of the draggable.
var grid = $('<div>', {'id': 'grid'});
var gridWidth = $('.draggable-block').width()/5;
var guideLinePos = gridWidth;
var guideLabel = "";
while(guideLinePos <= 1000) {
if(((guideLinePos - gridWidth) % gridWidth) == 0) {
guideLabel = "<div class='guide-line vertical-line'></div>";
$(guideLabel).css( "left", guideLinePos+"px" ).appendTo(grid);
}
guideLinePos = (guideLinePos + gridWidth);
}

Unfortunatly the JS fiddle either does not illustrate the issue : or the problem is the object cant be divided evenly by the grid (IE: a 60px*60px block does not fit well in a 40*40 grid)
I would suggest you take a look at the Gsap Draggable Library for tackling this issue. It does quite a good job of tackling the issue.

Rotating a shape in KineticJS seems to move it out of sync with it's group

I am working on some image viewing tools in KineticJS. I have a rotate tool. When you move the mouse over an image, a line appears from the centre of the image to the mouse position, and then when you click and move, the line follows and the image rotates around that point, in sync with the line. This works great.
My issue is, I have the following set up:
Canvas->
Stage->
Layer->
GroupA->
GroupB->
Image
This is because I draw tabs for options on GroupA and regard it as a container for the image. GroupB is used because I flip GroupB to flip the image ( and down the track, any objects like Text and Paths that I add to the image ), so that it flips but stays in place. This all works well. I am also hoping when I offer zoom, to zoom groupb and thus zoom anything drawn on the image, but for groupA to create clipping and continue to support drag buttons, etc.
The object I am rotating, is GroupA. Here is the method I call to set up rotation:
this.init = function(control)
{
console.log("Initing rotate for : " + control.id());
RotateTool.isMouseDown = false;
RotateTool.startRot = isNaN(control.getRotationDeg()) ? 0 : control.getRotationDeg();
RotateTool.lastAngle = control.parent.rotation() / RotateTool.factor;
RotateTool.startAngle = control.parent.rotation();
this.image = control.parent;
var center = this.getCentrePoint();
RotateTool.middleX = this.image.getAbsolutePosition().x + center.x;
RotateTool.middleY = this.image.getAbsolutePosition().y + center.y;
this.image.x(this.image.x() + center.x - this.image.offsetX());
this.image.y(this.image.y() + center.y - this.image.offsetY());
this.image.offsetX(center.x);
this.image.offsetY(center.y);
}
getCentrePoint is a method that uses trig to get the size of the image, based on the rotation. As I draw a line to the centre of the image, I can tell it's working well, to start with. I've also stepped in to it and it always returns values only slightly higher than the actual width and height, they always look like they should be about what I'd expect, for the angle of the image.
Here is the code I use on mouse move to rotate the image:
this.layerMouseMove = function (evt, layer)
{
if (RotateTool.isRotating == false)
return;
if (!Util.isNull(this.image) && !Util.isNull(this.line))
{
if (Item.moving && !RotateTool.isRotating)
{
console.log("layer mousemove item moving");
RotateTool.layerMouseUp(evt, layer);
}
else
{
var pt = this.translatePoint(evt.x, evt.y);
var x = pt.x;
var y = pt.y;
var end = this.getPoint(x, y, .8);
RotateTool.line.points([this.middleX, this.middleY, end.x, end.y]);
RotateTool.line.parent.draw();
RotateTool.sign.x(x - 20);
RotateTool.sign.y(y - 20);
var angle = Util.findAngle({ x: RotateTool.startX, y: RotateTool.startY }, { x: x, y: y }, { x: RotateTool.middleX, y: RotateTool.middleY });
var newRot = (angle) + RotateTool.startAngle;
RotateTool.image.rotation(newRot);
console.log(newRot);
}
}
}
Much of this code is ephemeral, it's maintaining the line ( which is 80% of the length from the centre to my mouse, as I also show a rotate icon, over the mouse.
Sorry for the long windedness, I'm trying to make sure I am clear, and that it's obvious that I've done a lot of work before asking for help.
So, here is my issue. After I've rotated a few times, when I click again, the 'centre' point that the line draws to, is way off the bottom right of my screen, and if I set a break point, sure enough, the absolute position of my groups are no longer in sync. This seems to me like my rotation has moved the image in the manner I hoped, but moved my group off screen. When I set offsetX and offsetY, do I need to also set it on all the children ? But, it's the bottom child I can see, and the top group I set those things on, so I don't really understand how this is happening.
I do notice my image jumps a few pixels when I move the mouse over it ( which is when the init method is called ) so I feel like perhaps I am just out slightly somewhere, and it's causing this flow on effect. I've done some more testing, and my image always jumps slightly up and to the right when I move the mouse over it, and the rotate tool continues to work reliably, so long as I don't move the mouse over the image again, causing my init method to call. It seems like every time this is called, is when it breaks. So, I could just call it once, but I'd have to associate the data with the image then, for the simple reason that once I have many images, I'll need to change my data as my selected image changes. Either way, I'd prefer to understand and resolve the issue, than just hide it.
Any help appreciated.

KineticJS - Moving 4000 tiles with Stage.draggable

(Sorry if this is a duplicate, but I don't think it is)
Just so you know, I'm using Google Chrome 29.0.1547.66 m.
I have a KineticJS Project going on at the moment which builds a tiled "staggered" map 40 x 100 tiles. The map takes about 500ms to render which is fine. All 4000 tiles have been put onto one layer.
Once that has completed, I try to drag the stage but I am getting very poor performance as it tries to move all 4000 tiles at once. We are talking about 160ms of CPU time.
I have tried breaking each row up into its own separate layer as others suggested, but that made it even worse (620ms CPU time) as it had to move each layer separately.
I wouldn't say I'm very good at JavaScript but I can't see a way to improve the performance of the drag and I have done some descent research.
Maybe caching the entire layer or something could work?
The project so far has quite a lot of code, so I'm just going to show snippets:
//Stage Object
window.stage = new Kinetic.Stage({
container: element,
width: 800,
height: 600,
draggable: true
});
//Map Loop for create and position tiles
var tempLayer = map.addLayer(); //makes a new layer and adds it to stage etc.
for (var y = 0; y < height; y++) { //100 tiles high
for (var x = width-1; x > -1; x--) { //40 tiles wide
var tileImg = map._tiles[mapArray[x][y]-1]; //map._tiles is just an array of Kinetic.Image objects
if (typeof(tileImg) != "undefined"){
var tileClone = tileImg.clone();
map.place(x, y, 0, tileClone, tempLayer); //places tile in world scope positions
}
}
}
tempLayer.draw();
If I can't work out how to improve the performance, there is no way anyone will be able to run this and the project is going to have to be binned, so all thoughts are appreciated! Thanks!

Have a look at this SO Question: How to cache a whole layer right before dragstart and revert it back on dragend?
The question and my answer describes a similar issue and I think the solution I came up with may help.
Basically what I was suggesting (although I haven't tried it completely so I don't know if it will work well):
Cache the layer using toImage
Drag the image on a different layer while hiding the original layer.
Calculate dx and dy (the distance that you moved)
Update the original layer with dx and dy
Hide image layer, show shapes layer.
I managed to create a quick example JSFIDDLE to work with so check it out. One thing I noticed is that the stage size really affected the performance of the drag, even if it was just 1 rectangle instead of 4000. So, if the stage is really big, even with this image caching thing it didn't really help. But when I decrease the stage size it seems to help
UPDATE:
I found the reason for that "stretched/scaled" image when dragging. It's because I had the image size set statically like so:
var image = new Kinetic.Image({
image: img,
x: 0,
y: 0,
width: 2000,
height: 5000
});
This caused the image to stretch since the image was larger than the stage. If we remove the width and height properties like so:
var image = new Kinetic.Image({
image: img,
x: 0,
y: 0
});
You'll see that the image doesn't stretch anymore.
The other good news is that I reduced the stage dimensions by half (although the number of rectangles, area taken by rectangles and size of image remains the same) and the performance has improved greatly. Hopefully your stage dimension isn't as large (2000x5000) as I had it before right? Check the JSFIDDLE now and see it in action!