Posts in the Tech Category

Grid-Powered Drop Quotes

Published 7 years, 10 months past

I’ve been experimenting with CSS Grid for various layout treatments — not high-level, whole-page layouts, but focused bits of design.  I’d like to share one of them for a few reasons.  Partly it’s because I like what I came up with.  More importantly, though, I think it illustrates a few principles and uses of CSS Grid that might not be immediately intuitively obvious.

First, here’s an interactive demo of the thing I’m going to be talking about.  You can use the checkboxes to alter aspects of the example, whether singly or in combination.  Feel free to fiddle with them before reading the rest of the article, or but you’ll probably want to come back to the demonstration as you read.  There’s also an external version of the demo as a standalone file, if you prefer opening it in a new tab and flipping back and forth.

So that’s how things have been laid out since the middle of 2005, more or less. I fiddled with a flexbox layout at one point as an experiment, but never shipped it, because it felt clumsy to be using a one-dimensional layout tool to manage a two-dimensional layout. I probably should have converted the navigation bar to flexbox, but I got distracted by something else and never returned to the effort.

Besides, Grid was coming. In the run-up to Grid support being released to the public, I was focused on learning and teaching Grid, creating test cases, and using it to build figures for publication.  And then, March 7th, 2017, it shipped to the public in Firefox 52.  I tweeted and posted an article and demo I’d put together the night before, and sat back in wonderment that the day had finally come to pass.  After 20+ years of CSS, finally, a real layout system, a set of properties and values designed from the outset for that purpose.

And then I decided, more or less in that moment, to convert my personal site to use Grid for its main-level layout.  It took me less than five minutes…

Let’s dig in!  The core concept here is a Grid-powered version of the big drop-quote on the left side, there, which is a relatively common treatment for blockquotes.  To make this happen, I’ve applied display: grid to the blockquote element itself, and added the opening quote using generated content, like so:

blockquote {
   display: grid;
   grid-template-columns: -webkit-min-content 1fr;
   grid-template-columns: min-content 1fr;
}
blockquote::before {
   grid-column: 1;
   content: "“";
   font-size: 5em;
   font-weight: bold;
}

There’s more to the actual styles of both rules, but that’s the central thesis: set up a two-column grid, and generate a great big opening quote.

The first thing to note here is that generated content also generates a pseudo-element that can be styled.  You may already realize this, since it’s known we can style generated content separately from the main content of the element.  But given that, if a grid is applied to the element, then any generated content’s pseudo-element, whether ::before or ::after, will become a grid item.  You can then place it in the grid.

I first came across this concept in the comments on my ALA article “Practical CSS Grid”, where Šime proposed using generated elements as a hack to get around the inability to directly style grid cells.  Here, I’m just using one to push a quote over to the side.

Why do this, when we can already use floats or relative/absolute positioning approaches to do the same?  Because it’s not quite the same: with Grid, the column containing the drop-quote responds to any changes to the quotation symbol.  Change the font, change its size, have the preferred font fail and fall back to an unexpected face, or replace the character with an SVG image, and the first column will resize thanks to the min-content track sizing, and the actual main content of the blockquote will adjust its placement to accommodate.  That didn’t happen with earlier techniques.

And yes, there is a vendor prefix in there.  Safari’s 10.1 Grid support came with -webkit- prefixed versions of min-content, max-content, and fit-content.  So I did the old pattern of prefixed first, unprefixed second.  This should be necessary only until the next release; Safari has already dropped the prefixes in its latest Technology Preview builds.  The change apparently just didn’t quite make the cut for 10.1.  It’s sad, but it’s also temporary.

In the meantime, this does mean that if you want to restrict your Grid styles only to implementations that don’t require prefixes, use that in your feature queries:

@supports (grid-template-columns: min-content) {…}

That, as well as a number of close variants like using grid-template-rows or max-content, will keep your Grid styles away from Safari until they update their Grid support in the public release channel.

That’s all nice, but there’s a great deal more to learn!  If you use the “Border” checkbox in the demo, you’ll see a dotted red border around the drop quote’s pseudo-element.  Notice that it matches the height of the opening paragraph, not the entire height of the blockquote.  That’s because the pseudo-element and the first paragraph share a row track.  The following paragraphs are in their own row tracks.

This brings up two things to consider.  First, all the child elements of the blockquote are now grid items.  That means the drop quote’s pseudo-element, but also all the paragraphs contained by the blockquote.  The same would happen to any child elements.  We could get around that by wrapping all the contents of the blockquote in a div or something like that, but I’d rather not.  So, this grid has four grid items: the pseudo-element, and three paragraphs.

This leads us to the second consideration: without placing the paragraphs into the same column, they’ll auto-flow into whatever grid cells are available.  You can see this by selecting the “Auto placement” option.  The first column will contain the quote and the second paragraph, as narrow as they both can be due to min-content.  The second column will contain the first and third paragraphs.

How I get around this in the working version is to explicitly put all the paragraphs — really, all child elements of the blockquote, which just happen in the case to be paragraphs — into the second column, like this:

blockquote > * {grid-column: 2;}

Okay, but how do they end up stacked vertically?  After all, I didn’t assign each of those child elements to a row, did I?

Wait a minute.  What rows?

If you go back and look at the CSS I showed, there is nothing about rows.  The property grid-template-rows exists, but I didn’t use it.  All I did was define columns.

Each child element goes into a row of its own anyway, because Grid has the ability to automatically create columns or rows when needed.  Suppose you define a three-by-three grid, and then assign a grid item to the fifth column of the fourth row.  What should happen?  The browser should auto-create as many columns and rows as needed.  Any auto-created tracks will have zero width or height if they don’t contain any grid items, unless you size them using grid-auto-columns or grid-auto-rows, but we’re not going there today.  The point is, here I’ve said all of the blockquote’s child elements should go into column 2.  Given that, they’ll auto-fill rows as available and auto-create rows as needed, filling them in once they’re created.

So the blockquote in the demo above has two columns because I explicitly defined them, and three rows because that’s what it needed to create to handle the three child elements.  If I’d added two more paragraphs and an unordered list, the grid would have had two columns and six rows (because six chid elements).

There are a lot of possible extensions to this technique.  A close quote could be created using ::after and placed in the last row of the grid, thanks to the ability to use negative track values to count back from the end of the grid.  Thus:

blockquote::after {
   grid-column: 3;
   grid-row: -1;
   content: "”";
   font-size: 5em;
   font-weight: bold;   
}

That places the close-quote in the third column, so to the right of the quoted text, and in the last row, regardless of how many rows were auto-created.  Of course, there is no third column…or there wasn’t, until assigning something to the third column.  At the point, the browser created it.

The danger there is that the auto-generated column is essentially tacked on to the trailing edge of the grid, without real consideration for what might be in the way — up to and including the edge of the viewport. Rather than auto-generate the column, we could define a third column like so:

grid-template-columns: min-content 1fr min-content;

This sets up a column on each side of the grid, one for each of the big quotes.  The second column, the one that gets all the actual child elements of the blockquote, receives all the space left over after those outer columns are sized, thanks to its 1fr value.

There’s one more drawback here, albeit one that’s easily overcome.  Grid items’ margins do not collapse.  You can see this effect by checking the “Default margins” option in the demo.  That shows what happens if default paragraph margins are allowed to remain.  We end up with two ems of space between the paragraphs, because each has top and bottom margins of 1em.

In the normal flow, margins collapse to the largest of the adjacent margins, which is why we’re used to 1em of space between adjacent paragraphs.  With grid items, what we see instead is the full element box, margins and all, placed inside the grid cell(s) they occupy.  That means any margin will create space between the edge of the grid cell and the border-edge of the element.  The fix here is straightforward: add a style to reduce margins between elements.  For example, something like:

blockquote > * {
   grid-column: 2;
   margin: 0.5em 0;
}

With a half-em margin above and below each element, any two adjacent elements will have the common 1em separation.  The demo actually has less than that because I wanted to use the print convention of paragraphs with the first lines indented, and a minor separation between paragraphs.  So the actual demo styles are more like this:

blockquote > * {
   grid-column: 2;
   margin: 0.125em 0;
   text-indent: 2.5em;
}
blockquote > *:first-child {
   text-indent: 0;
}

So there you have it: a Grid-powered drop quote.  I should note that all this by itself isn’t quite sufficient: if Grid isn’t supported, it will degrade poorly, as you can verify with the “Disable grid” option.

This is where using @supports() to encapsulate the Grid styling comes in handy.  You can put all of the quote-generation styles into the @supports() block, so that downlevel browsers just don’t get the drop quotes; or, you can set up the drop quotes with floats or positioning and then override those with @supports()-protected Grid styles.  Either one works.

Fortunately, we do have that capability, so it’s fairly easy to progressively enhance your designs with little touches like this one, even if you’re not ready for a full-on Grid plunge.  I’m looking forward to deploying this pattern here on meyerweb, as part of a site design overhaul I’ve been working on for the past couple of weeks.  That’s right: I’m working on my first redesign in a dozen years.  If that doesn’t give you some sense of the power of Grid, well, I just don’t know what will.


There is a followup to this article that explains and corrects an oversight in this article.


Practical CSS Grid

Published 7 years, 10 months past

…In the run-up to Grid support being released to the public, I was focused on learning and teaching Grid, creating test cases, and using it to build figures for publication.  And then, March 7th, 2017, it shipped to the public in Firefox 52.  I tweeted and posted an article and demo I’d put together the night before, and sat back in wonderment that the day had finally come to pass.  After 20+ years of CSS, finally, a real layout system, a set of properties and values designed from the outset for that purpose.

And then I decided, more or less in that moment, to convert my personal site to use Grid for its main-level layout.

Me, writing for A List Apart, taking you on a detailed, illustrated walkthrough of how I added CSS Grid layout to meyerweb.com, while still leaving the old layout in place for non-Grid browsers.  As I write this, Grid is available in the latest public releases of Firefox, Chrome, and Opera, with Safari likely to follow suit within the next few weeks.  Assuming the last holds true, that’s four major browsers shipping major support in the space of one month.  As Jen Simmons hashtagged it, it’s a new day in browser collaboration.

As I’ve said before, I understand being hesitant.  Based on our field’s history, it’s natural to assume that Grid as it stands now is buggy, incomplete, and will have a long ramp-up period before it’s usable.  I am here to tell you, as someone who was there for almost all of that history, Grid is different.  There are areas of incompleteness, but they’re features that haven’t been developed yet, not bugs or omissions.  I’m literally using Grid in production, right now, on this site, and the layout is fine in both Grid browsers and non-Grid browsers (as the article describes).  I’m very likely to add it to our production styles over at An Event Apart in the near future.  I’d probably have done so already, except every second of AEA-related work time I have is consumed by preparations for AEA Seattle (read: tearing my new talk apart and putting it back together with a better structure).

Again, I get being wary.  I do.  We’re used to new CSS stuff taking two years to get up to usefulness.  Not this time.  It’s ready right now.

So: dive in.  Soak up.  Enjoy.  Go forth, and Grid.


Getting Grid

Published 7 years, 11 months past

That converting-meyerweb-to-Grid article I’ve mentioned previously is still coming along (3,999 words as of the last draft, and I realized last night it needs another few hundred) and I think it will be out within a week.  I’ll do my best!  In the meantime, I’d like to point you to a few resources from the end of the article, plus do a tiny bit of self-promotion.

Resources first!  If you’re wondering what Grid means for Flexbox, Chen Hui Jing has a lovely piece on “Grid + Flexbox: the best 1-2 punch in web layout”.  Just the right length, with live Codepens, this is a very good introduction to using Grid and Flexbox in harmony.  Some of what’s described there won’t be as necessary in the future, as Flexbox-style alignment migrates to Grid, but in the meantime Hui Jing explores the current state of the art with elegance.

If you have Firefox or Chrome and they’re updated to the latest release (FF52, C57) then I strongly encourage you to set aside a few minutes and go browse The Experimental Layout Lab of Jen Simmons.  Jen’s been creating Grid demonstrations and experiments for well over a year now, and there are some really great examples there, summarizing some common design patterns and showing how Grid can make them much simpler and more robust.  I especially recommend the 2016 home page, which combines CSS Grid, writing modes, transforms, and design history to create something really great (try resizing to see the responsive coolness).  But don’t stop there!

If you like your learning in motion, Rachel Andrew’s video series introducing Grid concepts and properties is fabulous.  As an application developer — she’s part of the Perch CMS team — she’s been excited about Grid and what it can do longer than just about anyone.  Her deep technical skills and teaching abilities really come together in the video series.  If you prefer to read up on Grid, then Rachel’s written a series of articles for the Mozilla Developer Network that cover similar ground.

Finally, if you like extended technical explanations of every Grid property and value seasoned with lots of examples and screenshots, then I suggest picking up the Early Access version of CSS: The Definitive Guide, 4th EditionEstelle Weyl and I have been working on finishing this for a while now, and it’s just about ready: there are three chapters still to be added.  They’ve already been written, but haven’t quite finished first editorial review and production massaging.  But: the Grid chapter is already available, so if you get the book now, you’ll have instant access to something like 25,000 words going through Grid property by property.  And also a whooooole lot more words covering everything else in CSS.  (The current page count estimate for the book is 950.  Nine hundred fifty.  Yoinks.)

Go forth and Grid!


Chrome Grid Bug Update

Published 7 years, 11 months past

I mentioned late last week, in my post about Chrome 57 having landed Grid layout, that there is a bug that affects some people.  Well, further investigation has revealed that the bug doesn’t seem to be in the Grid layout engine.  Instead, disabling selected extensions makes the bug go away.

The odd part is that the extension seems to vary.  In my case, disabling Window Resizer fixed the problem.  Before you think it’s all their fault, though, Rachel Andrew discovered that disabling Window Resizer in her copy of Chrome did not solve the problem.  For her, it was disabling the LastPass extension that did it.  I don’t even have the LastPass extension installed on my machine, in any browser.

So: if you run into this problem, try disabling extensions to see if that fixes it.  If so, you can enable them one at a time and test to see which one triggers the bug.  With any luck, a fix will be found soon and deployed via auto-updating.  And if you find out anything else, please let us know on the bug report!


Doubled Grids

Published 7 years, 11 months past

Chrome 57 released yesterday, not quite a week ahead of schedule, with Grid support enabled.  So that’s two browsers with Grid support in the space of two days, including the most popular browser in the world right now.  Safari has it enabled in Technology Preview builds, and just blogged an introduction to Grid, so it definitely feels like it’ll be landing there soon as well.  No word from Edge, so far as I know.

I did discover a Chrome bug in Grid this morning, albeit one that might be fairly rare.  I filed a bug report, but the upshot is this: most or all of an affected page is rendered, and then gets blanked.  I ran into a similar bug earlier this year, and it seemed to affect people semi-randomly — others with the same OS as me didn’t see it, and others with different OSes did see it.  This leads me to suspect it’s related to graphics cards, but I have no proof of that at all.  If you can reproduce the bug, and more importantly come up with a reliable way to fix it, please comment on the Chromium bug!


Grid Inspection

Published 7 years, 11 months past

I said yesterday I would write up the process of adding Grid to meyerweb, and I did.  I started it last night and I finished it this morning, and when I was done with the first draft I discovered I’d written almost four thousand words.

So I pitched it to an online magazine, and they accepted, so it should be ready in the next couple of weeks.  Probably not long after Chrome ships its Grid implementation into public release, in fact.  I’ll certainly share the news when it’s available.

In the meantime, you can inspect live grids for yourself, whether here or at Grid by Example or The Experimental Layout Lab of Jen Simmons or wherever else.  All you need is Firefox 52, though Firefox Nightly is recommended for reasons I’ll get to in a bit.

In Firefox 52, if you inspect an element that has display: grid assigned to it, you’ll get a little waffle icon in the inspector, like so:

Mmmmmm, waffles.

Click it, and Firefox will draw the grid lines on the page for you in a lovely shade of purple.  It will even fill in grid gaps (which are a thing) with a crosshatch-y pattern.  It’s a quick way to visualize what the grid’s template values are creating.

If you have Firefox Nightly, there’s an even more powerful tool at your disposal.  First, go into the inspector’s settings, and make sure “Enable layout panel” is checked.  You may or may not have to restart the browser at this point — I did, but YEMV — but once it’s up and running, there will be a “Layout” panel to go with the other panels on the right side of the Inspector.  There you get the box model stuff, as well as a checklist of grids on the current page.

The Layout panel

For each grid on the page — not just the element you’re inspecting — you can set your own color for the gridlines, though those color choices do not currently persist, even across page reloads.  You can also turn on number labels for the grid lines, which are currently tiny and black no matter what you do.  And if you allow grid lines to extend into infinity, you can turn the page into a blizzard of multicolored lines, assuming there are several grids present.

This panel is very much in its infancy, so we can expect future enhancements.  Things like color persistence and better grid line labels are already on the to-do list, I’m told, as well as several more ambitious features.  Even as it is, I find it valuable in constructing new grids and diagnosing the situation when things go sideways.  (Occasionally, literally sideways: I was playing with writing-mode in grid contexts today.)

There’s another, possibly simpler, way to enable the Layout panel, which I learned about courtesy Andrei Petcu.  You type about:config into the URL bar, then enter layoutview into the search field.  Double-click “devtools.layoutview.enabled” to set it to “true”, and it will be ready to go.  Thanks, Andrei!

So go ahead — inspect those grids!


Welcome to the Grid

Published 7 years, 11 months past

Grid is public.  It’s live right now in the latest Firefox release, Firefox 52.

It will similarly be live in the next public Chrome release, due in the next week or so.

It’s here.  I almost can’t believe it.

For well more than a decade now, when asked what CSS needs more than anything, I’ve said it needs real, actual layout.  “A layout-shaped hole at its heart” is a phrase I may have used a fair few times.

Rachel Andrew had a great article last week about “Learning CSS Grid Layout”, which charts a sensible course for getting used to grid.  It also busted a few myths about grid.  I recommend it highly.

There’s one more myth I’d like to do my best to bust, which I’ll summarize as a comment I’ve seen many times: “Ugh, tables again?”

The underlying assumption here is: grids are just tables with a new syntaxThis is entirely untrue.

I mean, yes, you can recreate 1990s-era table-based layout techniques with grid, in much the same way you can recreate the submit button with two JS libraries and a complex front-end framework.  The ability to do it doesn’t necessarily make it a good idea.

(Though you might, from time to time, find the ability useful.  Here’s what I mean: you can take a bunch of data contained in arbitrary markup someone else is producing, and lay it out in a tabular format.  It would be far preferable to have the data in actual table markup, but if that’s not an option, grid will give you a potential solution.)

I have an example of just one way grids are different than tables.  I just last Friday finished writing the last chapter of CSS: The Definitive Guide, 4th Edition, covering filters, blending, clipping, and masking.  (I finished the grid chapter late last year, so it’s already available in the early-access title.)  Almost all the figures in the book were created by building HTML+CSS pages, and taking high-resolution screen captures with Firefox’s screenshot command.  Here’s one.

Compositing masks

The way these are displayed is actually the inverse of their source order.  I wanted them to be in document source such that the compositing steps were in chronological order, so that’s how I wrote them.  Once I laid them out that way in the figure, using grid, I realized it made more sense to arrange them visually, with the bottom layer at the bottom of the figure, the next above that, all leading up to the result at the top.

So I just rearranged them on the grid, by assigning grid row numbers.  The document source wasn’t touched.  A bit simplified, the CSS to do that looked something like this:


ol li:nth-child(1) {grid-row: 4;}
ol li:nth-child(2) {grid-row: 3;}
ol li:nth-child(3) {grid-row: 2;}
ol li:nth-child(4) {grid-row: 1;}

Because the compositing examples (the “columns” in the layout) were represented as ordered lists, with the grid set up to place each image with some captioning, I could just change their order.  So yes, it looks like a table, but the underlying structure is anything but table-like.  Just to get each column of examples grouped together with tables, I’d have to nest tables, or accept a one-row table with each cell containing some other structure.  Rearranging the columns would mean doing markup surgery, instead of just reassigning their layout placement via CSS.

Instead, I was able to represent the content in the best available structure (ordered lists) and then arrange them on a grid in the best way I could visually.  For that matter, I could responsively change the layout from a six-column grid to a three-column grid to un-gridded lists as the viewport got more and more narrow.  As, in fact, I did — check it out.  If you make the window narrow enough, Grid is dropped entirely so you can see the base structure and content.

This ability to place grid items without respect to source order is a powerful tool, and like all powerful tools it can be used for good or ill.  It’s possible to assemble a visually usable layout out of the most inaccessible, horrible markup structures imaginable.  It’s also possible to assemble a visually usable layout from clean, accessible markup in ways we’ve never even dared dream.

Combine grids with other CSS features, and you can really create art.  Jen Simmmons has a layout lab site, and her 2016 main-page design is… well, go see it in a grid-capable browser, like today’s release of Firefox.  Realize it’s all text, no images, no scripting.  Just markup and style.

And the style is remarkably simple for what’s being accomplished.  It’s not too alien a syntax, but it will likely take some time to adjust to using it.  It’s taken me some time, as I’ve experimented and written about it.  Unlearning my float habits has taken some work, and I don’t know that I’m completely done.  I do know that it’s been worth it many times over.

I’ve done a few experiments with the layout of a local copy of meyerweb, and done some frankly goofy things to the design along the way.  I’m hoping to convert what’s up here to a simple grid layout in the next few days, make it a slightly more complex grid shortly after that, and then maybe — maybe — actually do some redesigning for the first time in over a decade, to take advantage of grid more fully.  Jen has a great six-minute video exploring a few features of grid and the grid inspection tool now built into Firefox, which I recommend to anyone curious to know more.

So if you’re thinking of grid as tables 2.0, please, stop.  Table-style layouts are the first one percent of what grid offers.  There are works of art and undiscovered techniques waiting in the other 99 percent.


Scaling SVG Clipping Paths for CSS Use

Published 7 years, 11 months past

I’ve been working a lot with the clip-path property recently, as I write the chapter on filters, blends, clipping, and masking for CSS: The Definitive Guide’s long-delayed 4th edition (available now in early-release format!).  One of the nifty things you can do with clipping paths is define them with percentage-based coordinates.  For example, here’s a hexagon-like clipping path:

clip-path: polygon(50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%);

That starts at the center top (50% 0), goes to the right edge, quarter-down (100% 25%), and so on.

When I got to SVG-based clipping, which you can use with the CSS pattern clip-path: url(#pathID), I tried and failed with this:

<clipPath id="hexlike">
  <polygon points="50% 0, 100% 25%, 100% 75%, 50% 100%, 0 75%, 0 25%" />
</clipPath>

It didn’t work because, as I discovered to my horror, SVG does not allow percentage coordinates.  I could just strip all the percent signs out, but that would be the same as saying this in CSS:

clip-path: polygon(50px 0, 100px 25px, 100px 75px, 50px 100px, 0 75px, 0 25px);

I didn’t want pixels, though.  I want percentages, darn it all!

So I asked around on Twitter, and Markus Stange pointed me to the solution: converting all the SVG coordinates to the range 0–1 and using the clipPathUnits attribute.  The working version looks like this:

<clipPath id="hexlike" clipPathUnits="objectBoundingBox">
  <polygon points="0.5 0, 1 0.25, 1 0.75, 0.5 1, 0 0.75, 0 0.25"/>
</clipPath>`
A hexlike clipping path.

That yields the same result as the polygon() CSS shape with the percentages I showed before.

All that is great if you’re writing your own SVG shapes and can make sure you set it up properly, but what if someone hands you a shape to be used as a clip path and it’s in absolute coordinates like 100 75?  If you’re really lucky, the shape has a viewbox of 0 0 100 100 (or all the coordinate points are in that range) and you can just divide all the coordinate points by 100 to get the proper values.  But that’s really tedious for any but the simplest of shapes, and besides, what if it has some other viewbox?  That’s where the transform attribute saves the day.

For example, suppose you get an SVG file that looks like this (with the actual path coordinates removed because there are a lot of them):

<svg version="1.1" xmlns="http://www.w3.org/2000/svg"
  xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 329.6667 86">
  <clipPath id="cloud02">
    <path d="…(coordinates go here)…"/>
  </clipPath>
</svg>

First, add the clipPathUnits attribute to the <clipPath> element:

<svg version="1.1" xmlns="http://www.w3.org/2000/svg"
 xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 329.6667 86">
  <clipPath id="cloud02" clipPathUnits="objectBoundingBox">
    <path d="…(coordinates go here)…"/>
  </clipPath>
</svg>

Next, look at the viewBox attribute on the <svg> element itself.  The value there is 329.6667 86.  That means 329.6667 coordinate units horizontally, and 86 units vertically.  So all you need to do now is divide all the horizontal values by 329.6667, and the vertical values by 86.  Which would be super tedious, except we have scaling transforms at our disposal:

<svg version="1.1" xmlns="http://www.w3.org/2000/svg"
  xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 329.6667 86">
  <clipPath id="cloud02" clipPathUnits="objectBoundingBox"
   transform="scale(0.003033 0.0116279)">
    <path d="…(coordinates go here)…"/>
  </clipPath>
</svg>

Those two values are 1/329.6667 and 1/86, respectively, and they effectively scale every point in the d attribute to fit into the needed 0–1 range.  (That’s not precisely what happens, but the outcome is the same.)  Thus we have an SVG clipping path that scales with the element and fits to its dimensions!

This works just as well for other markup patterns.  To return to the hexlike path from before, assume it was written like this:

<svg version="1.1" xmlns="http://www.w3.org/2000/svg"
 xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 100 100">
  <clipPath id="hexlike">
    <polygon points="50 0, 100 25, 100 75, 50 100, 0 75, 0 25" />
  </clipPath>
</svg>

If that were applied as-is, via clip-path: url(#hexlike), it would create a hex-like clipping path that fits a 100px by 100px box, positioned in the top left of the element (in left-to-right languages, I presume).  The quick fix:

<svg version="1.1" xmlns="http://www.w3.org/2000/svg"
 xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 100 100">
  <clipPath id="hexlike" clipPathUnits="objectBoundingBox"
   transform="scale(0.01)">
    <polygon points="50 0, 100 25, 100 75, 50 100, 0 75, 0 25" />
  </clipPath>
</svg>

Bingo bango bongo, it will now scale to the element’s dimensions, whatever those turn out to be.

Of course, if you apply that to something like a short paragraph, it will be verrrrry stretched out, but the same would be true with a percentage-based polygon() shape.  The beauty here is that you can scale any coordinate set, so if you have a tiny path that you want to blow up, or a huge path you want to shrink down, you can transform it without using clipPathUnits to stretch it over the bounding box.  Something like this:

<svg version="1.1" xmlns="http://www.w3.org/2000/svg"
 xmlns:xlink="http://www.w3.org/1999/xlink" viewBox="0 0 100 100">
  <clipPath id="hexlike" transform="scale(4)">
    <polygon points="50 0, 100 25, 100 75, 50 100, 0 75, 0 25" />
  </clipPath>
</svg>

That gets you a hexlike shape that fits a 400px by 400px box, for example.

Now all CSS needs is the ability to size and position clipping paths in a manner similar background images, and we’ll be in clover.  I hope such properties are in the WG’s mind, because I’d love to be able to just point an at SVG clipping path, and then say something like clip-path-position: center; clip-path-size: contain;.  That would remove the need for fiddling with SVG attributes altogether.

Thanks to Markus Stange for the technique and his invaluable assistance in proofreading this article.


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