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zoom in on a particular area in a line chart (using d3 and svelte)

I am trying to zoom in on parts of a line chart using viewBox. I managed to get it working, however, not sure how to deal with the fact that everything scales accordingly (line path also becomes larger).
What I am looking for is for the line to stay constant while zoom is happening. I researched that there is also a way with translation and scale, but not sure how to implement it.
Also, not sure how to make this behavior more automatic. For example, I am zooming in on a range between two years: 2010 and 2011. Currently, I specify the y value manually. But ideally, this would be specified in using yScale function.
Any help would be appriciated!
Here is my repl: https://svelte.dev/repl/be0df7e353334108b3d432d5c82a6cd3?version=3.38.2

One way to accomplish this is by scaling the viewBox of the <svg> element.
You can do this by binding the x, y, width and height of the viewBox.
<svg ... viewBox="{x} {y} {width} {height}">
You can also tween the viewbox changes:
By using Svelte's tweened() store for x, y, width, height. ie <svg viewBox="{$x} {$y} {$width} {$height}">
Or by using SVG's <animate> element. ie <animate attributeName="viewBox" values="..." dur="2s"/>

Zoomable timeline with one element per tick (D3V6)

I'm working on a timeline-based chart that should always have one rect per x-axis tick. The idea is to use the color of each rectangle to convey the amount of data that's in that date (somewhat like a heatmap).
The chart also has grouped y values. That is, there are two y axes: one for each group, and inside each of those, three lines (subgroups). Semantically the intention is to say: "For this coupon, on this date, there are this many readings for each data type". To help clear up my intention further, this library has a very similar solution to what I'm aiming at.
OK, and your question...?
My question is about aligning the rectangles with the ticks, and keeping them that way. How can I make them always be aligned with the ticks? Is there a way to "tie" a rect to a tick?
To make matters worst, the chart has to be zoomable, so when you scroll and the dimensions of the ticks change, the rectangles should stick to their corresponding ticks: move with them, change their width accordingly and so on. Basically, I'd like to "marry" the rects to their corresponding ticks.
What have you tried?
My approach right now is to make the segments' width depend on the current tick count, and essentially treat the current ticks as if they were my data.
That is:
segmentWidth = state.width() / ticks.length;
And when updating/rendering the rects:
state.mainG.selectAll('g.couponData')
.selectAll('g.column')
.data(ticks)
...
One problem I see with this is that if you click and drag, the ticks expand, so having a single, global segmentWidth doesn't seem like the right approach. Seems like I'd need a way to grab each tick and get the distance to the next one, and use that as the width of each corresponding segment, but I haven't quite got there yet.
Here's a fiddle with an example of what I have:
https://jsfiddle.net/bnekvp0o/11/
TBH, I presume I'm making some dumb calculation mistakes, but I also feel like I'm bruteforcing the solution, so I'm hesitant to keep trying to make it work with my current approach, since I'm quite new to the framework.
Thanks in advance!

JavaScript Canvas createPattern

I have problem with canvas createPattern. I have two boxes, both will move after pressing a keyarrow:
Example:
http://jsfiddle.net/wA73R/1/
The problem is that the box background filled by createPattern also is moving. How to avoid that? Is there any solution? The big box is only an example (drawImage is not the good solution for me, I need something that will repeat background image).
Thank you for help

The problem is that the box background filled by createPattern also is moving.
Actually your problem is that the background is not moving - it is static, while you are drawing your rectangle to different positions.
How to avoid that?
The pattern will always be drawn at the coordinate origin, whose actual position is defined by the current transformation. In future you will be able to transform the pattern itself with the setTransform method, but since that currently is not implemented anywhere you instead will have to change the global transformation matrix.
In your case it means, that instead of drawing your rectangle at x/y, you translate the whole context to x/y and draw your rectangle at 0/0 then:
ctx.fillStyle=pattern;
ctx.save();
ctx.translate(boxes[i].x - left , boxes[i].y);
ctx.fillRect(0, 0, boxes[i].width, boxes[i].height);
ctx.restore();
(updated demo)

Calculate new width when skewing in canvas

I'm using canvas for a project and I have a number of elements that I'm skewing. I'm only skewing on the y value and just want to know what the new width of the image is after skewing (so I can align it with another canvas element). Check out the code below to see what I mean
ctx.save();
//skew the context
ctx.transform(1,0,1.3,0,0,0);
//draw two images with different heights/widths
ctx.drawImage(image,0,0,42,60);
ctx.drawImage(image,0,0,32,25);
The goal would be to know that the 42 by 60 image was now a X by 60 image so I could do some translating before drawing it at 0,0. It's easy enough to measure each image individually, but I have different skew values and heights/widths throughout the project that need to be align. Currently I use this code (works decently for images between 25 and 42 widths):
var skewModifier = imageWidth*(8/6)+(19/3);
var skewAmount = 1.3; //this is dynamic in my app
var width = (skewModifier*skewAmount)+imageWidth;
As images get wider though this formula quickly falls apart (I think it's a sloping formula not a straight value like this one). Any ideas on what canvas does for skews?

You should be able to derive it mathematically. I believe:
Math.atan(skewAmount) is the angle, in radians, that something is skewed with respect to the origin.
So 1.3 would skew the object by 0.915 radians or 52 degrees.
So here's a red unskewed object next to the same object skewed (painted green). So you have a right triangle:
We know the origin angle (0.915 rads) and we know the adjacent side length, which is 60 and 25 for your two images. (red's height).
The hypotenuse is the long side thats being skewed.
And the opposite side is the triangle bottom - how much its been skewed!
Tangent gets us opposite / adjacent if I recall, so for the first one:
tan(0.915) = opposite / 60, solving for the opposite in JavaScript code we have:
opposite = Math.tan(0.915)*60
So the bottom side of the skewed object starts about 77 pixels away from the origin. Lets check our work in the canvas:
http://jsfiddle.net/LBzUt/
Looks good to me!
The triangle in question of course is the canvas origin, that black dot I painted, and the bottom-left of the red rectangle, which is the original position that we're searching for before skewing.
That was a bit of a haphazard explanation. Any questions?

Taking Simon's fiddle example one step further, so you can simply enter the degrees:
Here's the fiddle
http://jsfiddle.net/LBzUt/33/

Canvas coordinates in Fabric.js have offset

I just started with fabric.js and I have a (probably beginner) error:
I am using fabric with jquery with the following code:
$(document).ready(function () {
canvas = new fabric.StaticCanvas('scroller');
canvas.add(
new fabric.Rect({ top: 0, left: 0, width: 140, height: 100, fill: '#f55' })
);
});
This code should draw a 140x100 Rectangle on the canvas.
Sadly, only a quarter of the Rectangle appears.
If I change the top and left values to higher numbers, more of the Rectangle appears on the canvas.
So it seems, that the canvas origin is not at 0/0, but at sth. higher.
Does someone know how to fix this or what I am doing wrong?
Thanks in advance,
McFarlane

Here is a jsfiddle link with some examples http://jsfiddle.net/pukster/sdQ7U/2/
My guess is that fabric.js calculates everything from the origin (middle point) since it is drawing exactly one quarter of a rectangle even with a canvas 10 times the size of the rectangle. My guess is that top and left actually refer to the origin and not the top and left sides of the imaginary bounding box. Trouble is there is very little documentation on fabricjs. Is there any reason you are using fabricjs and not easeljs
EDIT Here's the same fiddle but with squares instead of rectangles (it is more clear) http://jsfiddle.net/pukster/sdQ7U/3/
EDIT OK I am now almost absolutely certain that fabric.js uses the center as the top/left. I ripped their example off of their site and overlayed it with the transparent couterpart to those shapes had they been coded in pure canvas http://jsfiddle.net/pukster/uathZ/2/ (blue border is the limit of the canvas element).
What you see is that the boxes are exactly offset by half but the circle (I only drew a semi circle otherwise it would not have been discernable) is perfectly overlapped. This is b/c in HTML Canvas, the circle coordinates (x,y) refer to the origin and not the top left. I did not bother with the triangle b/c my trigonometry is a bit rusty. I personally think it's misleading to use the terms top and left, when x and y would have been more representative and shorter.

Yes, this is highly unexpected and even more undocumented.
Workaround:
Set
originX: "left"
originY: "top"
for each created object.
edit: or use kangax simpler solution in the comment below.

I want to comment but lack the reputation to do so. So anyway, here is what happens when I do the following:
fabric.Object.prototype.originX = "left";
fabric.Object.prototype.originY = "top";
The shape gets rendered fine but when I select it for resizing or moving, it gets offset to a different location. The best approach seems to be to set the coordinates for every object separately using the set() method.