Making Emacs work like my Neovim setup

Table of contents

  1. Package management: from vim-plug to Package.el and use-package.
  2. Vim things and Evil things: experiences using Evil mode.
  3. Project management and file navigation: from fzf to Helm and Projectile.
  4. Specific packages: a small teaser on alternatives for popular Vim packages.
  5. Theming: everybody wants some eye-candy.
  6. Performance and server mode: naïve comparison of how Neovim and Emacs feel differently performance-wise.
  7. Conclusion and fare-thee-wells.

My configuration repositories

Do not expect extremely polished dotfiles. I know some of you will be pulling your hair out with some of the stuff you see here:

I will not give you counsel, saying do this, or do that. For not in doing or contriving, nor in choosing between this course and another, can I avail; but only in knowing what was and is, and in part also what shall be.

Galadriel

I’ve been a Neovim user and fan for a bit more than a year now. After having given it a reasonable spin I’ve become quite efficient at working with it, and it’s been a pleasure all the way through. Certainly, I’m a lot faster with my Tmux/Neovim/gitsh workspace than I was with either Atom, Sublime Text or VSCode, and I feel a lot more comfortable.

From this point and forward, and although I use Neovim, I’ll be using the words Vim and Neovim interchangeably. Whether I refer to the software packages or to a specific user community should be clear in context.

During the last weeks I’ve noticed several tools and concepts in the Emacs which I’ve found attractive enough to try out the platform. These include:

  • Org-mode: I’ve tried the Vim port and although it’s a wonderful effort at emulating the original Emacs package, I think it would require quite a bit of an investment to reach the current scope of Org-mode. I plan to use Org-mode for GTD and for generic notetaking; also being able to write my Emacs configuration in Org-mode is a beauty.
  • Magit: with my Tmux setup, I initialize several workspaces for each project with a script, and my standard workspace includes a Vim window, and another window with several panes. One of these is always a gitsh instance. It’s worked wonderfully for me but after having tried the Magit interface there’s no question that I’m going to be needing less keystrokes to do my thing, all while enjoying a beautiful interface.
  • Lisp: admittedly, I could do with Vim but Emacs has a Lisp interpreter at its core, and integration is granted. I don’t use Lisp at work and I’m a beginner, but it feels like it’s impossible to find anything about Lisp support in Vim where the Emacs solutions are not mentioned.
  • Integration: I like the never leave your editor and kitchen sink in Emacs approach and although I doubt I’ll ever manage emails or browse the web inside Emacs, I feel all warm and fuzzy when I realize I could if I wanted to. Many of these things are arguably possible in Vim but it feels like the Emacs community leans more towards it than the Vim counterpart.

So I decided to surrender to my sacrilegous self and try to emulate everything I do with Vim from an empty Emacs config file built with Org-mode. And I must say: it’s been a breeze! I haven’t even needed to dedicate much time to learning actual Emacs, and what I’ve learned has actually been nice. In this post I’ll try to go through what I did to rebuild my setup; I hope you’ll enjoy it as much as I did.

Package management

For package management needs the Vim community has contributed several awesome packages like Pathogen or vim-plug among the many worth mentioning. I’ve always used vim-plug and never found a problem with it. As active as the Emacs community is in regards to package development, I expected a solution that would provide the same level of comfort.

Emacs comes bundled with Package, and this is as much as I’m aware of: it takes care of package repository management, and to configure it I only needed to add the links to those repositories and initialize it.

Package, however, does not take responsibility for automatic fetching, updates, and encapsulation of configuration (which vim-plug does, and very well). For this, I’ve found the de-facto solution to be use-package. To be able to work with use-package using its minimal functionality, this is all you need to know:

  • use-package can fetch whatever packages are made available through your Package configuration.
  • A basic declaration looks like this: (use-package package-name).
  • If you add :ensure t, you’ll get automatic fetching of your package and startup checks: (use-package package-name :ensure t).
  • If you add :defer t, your package will load lazily: (use-package package-name :ensure t :defer t).
  • You can add :init, and everything you pass it will be evaluated before the package loads. Here’s where you’ll use (setq key 'value), for example.
  • You can add :config, and everything you pass it will be evaluated after the package loads. Here’s where you’ll initialize modes, for example.

It didn’t take me too long to learn this, and use-package allegedly does a thousand more things which I’ll begin to learn with time.

Vim things and Evil things

Evil calls itself the extensible vi layer for Emacs, and claims that it emulates the main features of Vim. I’d say this is an understatement; Evil feels like a complete re-implementation of Vim’s porcelain. It makes you feel right at home once you start using it:

  • Macros: these work exactly as expected. Even making a visual selection and running :norm @q runs your q macro on the visual selection, just like in Vim. The only difference I’ve noticed is that execution is minimally slower, but the decrease in speed does not compare to that of VSCode’s implementation of Vim macros, for example.
  • Registers: registers also work exactly as expected. The only problem I’ve had is that I can’t copy to the clipboard by using the + register, but this must be a misconfiguration on my part for Emac’s clipboard integration, so I suspect it won’t be a huge effort to fix it.
  • Command repetition (.): works as expected, except for some actions introduced by other packages. One of these, unfortunately, is evil-surround. Here’s the related issue.
  • Auto-save and safety/backup features: they can be easily configured to not happen at all or to happen in a specified directory (I’m using /tmp).
  • Ex commands (those starting with a colon :) like substitution, substitution with manual confirmation, invocation of macros in normal mode, etc. All work great and I haven’t found an instance where they don’t.
  • Marks: I don’t make extensive use of them, but they also seem to be working great.

Using evil-leader you can configure a leader key. I’ve configured mine to Space, and added a several keybindings. The same results can be achieved with the more powerful general.el, and if you need chained keystrokes to produce a command (for example, I used to have <leader> wq, which I found faster than :wq), you can use Hydra. I haven’t found a need for these and I’m doing just fine with evil-leader.

Project management and file navigation

My setup using Vim is basically fzf (which I use for many more things outside Vim) powered by Ag (or The Silver Searcher) for finding files and ripgrep for finding text in a project. This works flawlessly.

I’ve found the combination of Helm and Projectile to be an adequate substitute to my former setup. On big projects like Servo, the difference in speed is noticeable (in favor of the Vim configuration) but I can live with that. I don’t know why, but there’s a longer load time on the Emacs setup.

The scope of fzf is by no means comparable to that of Helm and Projectile, so this is not meant to be a comparison but it does happen to be what covers my file-finding needs. Both setups enable extremely quick fuzzy search for files and content.

As you can see on my Emacs configuration, my setup for Helm and Projectile is extremely basic and I haven’t needed further customization yet. And I must say: they look much prettier than the Vim setup I use.

Specific packages

A quick search on your favorite engine will yield at least a couple different solutions to problems some of the nicest Vim plugins solve. Here’s a quick list to encourage you:

  • VimCompletesMe: I enjoyed the simplicity of VimCompletesMe, which basically only extends Vim’s autocomplete features and lets you use them by pressing Tab. I found that the Emacs package auto-complete provides the same ease of use and also feels lightweight.
  • vim-tmux-navigator: in Tmux, I use <my-tmux-prefix>-[hjkl] to navigate panes. Using Vim, I wanted windows to behave as if they were on the same level as Tmux panes, and vim-tmux-navigator works great for that. For Emacs there’s a port called emacs-tmux-navigator.
  • auto-pairs: Emacs has a built-in mode that suits my needs. Enable it with (electric-pair-mode 1).
  • NerdTree: the Emacs port NeoTree does the original justice and, although I haven’t gotten there yet, it can also be extended with Git integration and icons if you use GUI Emacs.
  • vim-emoji-complete: I use this to navigate and autocomplete through a list of Unicode emojis. In the company I work at, we use Gitmojis extensively, so this is actually an important part of my workflow. You should check them out too, it may seem silly but it’s quite helpful to be able to recognize what every commit does without even reading the message. For Emacs, there’s an even better solution for inserting emojis into your buffer: emojify. This thing even lets you customize the list of emojis you get. For example, I’ve chosen to only display Unicode emojis, and not GitHub or vanilla ASCII emojis.

Regarding Tim Pope plugins: there’s an Emacs port for everything Mr. Pope does. Many of these go on top of Evil, and it’s a no-brainer to add them and use them if you’re used to their Vim counterpart.

Theming

Themes are really easy to set up on Emacs. Just add a use-package declaration and then load it with (load-theme 'pretty-theme t). The second argument automatically answers “yes” to a couple security questions that pop up every time you load a new theme. Emacs themes can run arbitrary Elisp so they can do a lot of nasty stuff. Make sure you trust the sources where you get your themes.

If I had to complain about anything, I’d say most themes work much better on the GUI version of Emacs, and I use the terminal version (emacs -nw). Many themes’ backgrounds are broken and show up differently depending on your $TERM environment variable. Of the ones I’ve tried, I’ve found Monokai and Badger to work look best on terminal Emacs.

Performance and server mode

Neovim feels a lot snappier for a lot of interactions. This, however, is not important at all most of the time, because it never shows while writing or navigating text inside a buffer.

The main difference in performance shows in startup time. Here’s a quick-and-dirty comparison using time, with my full configuration loaded on both programs:

time nvim +q
nvim +q  0.13s user 0.02s system 97% cpu 0.160 total
➜  time em +q
emacs -nw +q  2.14s user 0.12s system 44% cpu 5.121 total

Please do not evaluate this as any kind of benchmark: I haven’t done anything to improve startup time on either Neovim or Emacs (like using use-package’s :defer t).

The two seconds of waiting is OK if you open Emacs once and work from there for each project. It is not OK if you’re using Emacs as a default editor for stuff like Git, or even your $EDITOR environment variable.

Emac’s solution to this is server mode. Basically, you start an Emacs server on your fully loaded instance (the one that took two seconds to open). From then on, if you want to open Emacs for a quick edit and you don’t need the default directory to be the one you called Emacs on, you can go emacsclient.

➜  time emacsclient -nw -c -a "" +q
emacsclient -nw -c -a "" +q  0.00s user 0.00s system 0% cpu 3.010 total

Yep - instant! That’s more like it. I have that gravely arcane command (emacsclient -nw -c -a "") set as my $EDITOR environment variable. Also, I have two aliases:

  • em opens a full Emacs instance.
  • e is used to manually call emacsclient -nw -c -a "", which is also my $EDITOR.

This is admittedly a lot of work compared to just having an editor that loads quickly all the time. But it works! You can see the section of my config file where I set up server mode (basically, there’s no setup).

Conclusion

Voilà! Now I can continue Vimming around. I can Vim around while writing Lisp comfortably, doing some GTD in Org-mode, using Magit, and having leveled up in snobbism 😭.

Jokes aside, it feels good to have given both editors a chance. I have certainly had a taste of why both communities are so passionate about their preferences. I’ll make another post as soon as I’ve discovered if I can actually use my new setup as fluently as my former configuration. Until then, happy new year!

My experience contributing to Servo

Some months ago a colleague introduced me to Rust and to the Servo project. It’s a web browser engine led by Mozilla, and its code is available on GitHub and is open to contributions.

Working on Servo was attractive to me from the start for several reasons:

  • It’s written in Rust, and Rust has an exciting community, it’s low level and modern, it’s not shackled in any way by existing legacy code nor by industry requirements, and it just seemed like the perfect thing to help me quench my learning thirst.
  • Servo is a web browser engine, and working for a web browser engine as a web developer feels like working on the biggest possible project, on the foundation on which everything I’d ever done took place.
  • Servo has an enormous amount of issues you’re welcome to take. Some of these may seem extremely cryptic and complicated for someone new, but others are extremely trivial. You’ll be sure to find the full gradient of difficulties in Servo issues, and there’s even Servo Starters, which uses GitHub labels to show issues that are Good first PRs.

Let’s talk about what actually working on the project feels like.

Finding an issue

First, you’ll need to find an issue you find interesting. Helpful labels are E-easy, Good first PR, and C-assigned. You can filter for issues that haven’t been assigned to anyone yet by searching with a negative prefix: -label:C-assigned. Here’s a good filter to start with:

is:issue is:open label:E-easy -label:C-assigned

Do not be discouraged by issues which don’t have the E-easy label on them. In my experience, an E-easy task could end up being a bit more complicated anyway: the line between easy and difficult is blurry and you’ll only find out what you’re facing once you start working on it.

Also, don’t forget Servo Starters.

Working on your task

Once you’ve found the issue you want to work on, make sure to leave a comment saying you’re working on it so there’s no two people implementing the same thing separately.

Compiling Servo is understandably slow: it’s a huge project. Your first run will likely take between thirty minutes and one hour depending on your machine and connection, and after some re-runs and testing you’ll find yourself with a 15GB directory.

Servo has its own tool, mach, which you can use to build for development (./mach build -d), for release (./mach build -r), and to do many other things. When you submit your pull request, it must pass some CI tests which you can try locally to save time:

If all of those pass, you’re almost safe to think it will pass the first CI tests. Check out the complete .travis.yml file to see the rest. Of course, even if your changes don’t pass the tests, you can submit your pull request and expect help from the Servo project members.

Submitting a pull request

What you need to do to submit a pull request is carefully explained in Servo’s Wiki Page about GitHub workflow. Once you submit your pull request, you’ll be promptly greeted by a dog. You won’t need to talk to bors-servo but Servo organization members can request CI retries by mentioning @bors-servo.

The review process and regression tests

If needed, you’re guaranteed to receive extensive help from the project maintainers. In fact, in some cases, I’m quite sure any of the Servo organization members could have solved the problem I was facing with less effort than it took to help me. Here’s some live proof. The help I receive when working on Servo makes for an invaluable learning opportunity and it makes contributing to the project all the more enjoyable. Do not be afraid to ask any doubts, and always do your research on the topic: if you study it enough, you’ll be able to discuss with others and learn even more.

Once your pull request is all green, you can request review by commenting r?. The time until somebody reviews your PR ranges between minutes and a day or two. Somebody will automatically be assigned to the pull request depending on the code area you’re working on. Servo organization members can request a full CI run by commenting @bors-servo try. This will trigger the rest of the CI suites, and the most important one is the Web Platform Tests. It’s a regression test suite used for Firefox a cross-browser regression test suite run for Firefox and (at least in part) by the Chrome, Edge and Safari teams (thanks for the correction jgraham). Many of the tests that run on the suite for Servo come directly from the WPT, but you can also write your own new tests, modify existing ones or modify the expectations for existing test results. Many tests are expected to fail for Servo, and you can also submit a pull request to fix those failures. Of my four pull requests to Servo, two of them have caused failures on the WPT suite and most of the work related to the issue went on fixing and improving the tests.

Running the full test suite takes a long time on CI. Usually around one hour. If a regression test fails live and you’re working on a fix, you can always run the test locally to avoid running the full suite online again. First, make a development build with ./mach build -d and then run the specific test with ./mach test-wpt [path-to-test]. Unexpected test results, such as PASS, expected FAIL will also make the CI suite fail: you’ll need to update the test expectations by modifying the corresponding .ini file. On the guide I linked above there’s all the information you need on how to work with the WPT suite.

Resources to help you figure out how to solve an issue

Of course, this is highly dependent on what type of issue you picked. But in general, the most important resource is documentation. Reading the HTML Living Standard is a great way to help you find the right way to solve a problem. Usually, all the problems are already solved and their solution is in the spec. You’re just writing a different explanation of their solutions… in Rust. Quoting Kevlin Henney:

The act of describing a program in unambiguous detail and the act of programming are one and the same.

You can also find a huge amount of valuable information in the Mozilla Developer Network. Pretty much the same as the spec, but with a lot of examples, and a lot more verbosity. Do not make the same mistake I did and skim through the examples trying to find the exact line that will solve your problem: reading everything thoroughly is what will help you understand the issue best.

If armed with a powerful enough tool, you’ll be able to document your way out of your issue by just reading the source code and searching inside of it. I know all editors have project search functionality but this is a huge project. As of commit b1d7b6bfcf, the Servo repository has a whopping 6,517,647 lines of code (that’s six and a half million). I used loc to count those. So use something fast like ripgrep: it’ll make your life a lot easier.

In the end, you’ll receive the most help from the project maintainers: just ask them. It’s an extremely fun process.

If you think I’ve missed a great resource, please comment below and I’ll be sure to include it in this post, and use it on my own as well.

Conclusion

Working on Servo is one of my main sources of learning nowadays and I’ll keep on trying to find issues I can tackle. The tasks I’ve carried out for now have ranged from a two line change dependency removal to properly setting the origin of fetch requests. The fetch API issue took me almost three months to get merged, mostly because of my lack of understanding of the project. But the project maintainers proved to be exceptionally helpful and pleasant to work with. They also never tried to rush a solution and always “followed” (and this should read “accommodated to” or “slowed down to”) my pace.

I encourage everyone reading this to check out the project and consider contributing to it. The time you spend working on a project like this is extremely valuable to you as a web developer, and in the end you can feel proud of helping build something on which your applications and websites will probably run in the future.

Why won't my text overflow? Where's my ellipsis!?

The text-overflow property is a PITA to deal with because on its own, it won’t force text to overflow. Say what? Its name IS text overflow. Anyway, what it actually does is to define the behavior of a text node if it overflows. The job of actually making it overflow is yours and only yours.

I present to you a checklist that should once and for all truncate that stubborn span and print some beautiful ellipses at the end of your one-liners.

In the checklist, I’ll be using the word “container”. So let’s define it first, just for this post: the “container” I’m talking about is the immmediate parent of the element that contains the text node you want to truncate. For example:

<div> <!-- This div is the container -->
  <span>I will NOT truncate. Nononononono, no!</span> <!-- Let's call this one "stubborn child" -->
</div>

Is your container NOT a flex container? Checklist A is your friend. Is your container a flex container? Checklist B is for you.

Checklist A: for non-flex containers

  1. Is the container a block-level element?
  2. Does the container have a computed size determined by your CSS, or does it inherit one?
  3. Did you add the white-space: nowrap; property to the container?
  4. Did you add the overflow: hidden; property to the container?
  5. Did you add the text-overflow: ellipsis; property to the container? (duh)

Checklist B: for flex containers

  1. Does the container have a computed size determined by your CSS, or does it inherit one?
  2. Does the child also have a computed size determined by your CSS, or does it inherit one?
  3. Did you add the white-space: nowrap; property to the child?
  4. Did you add the overflow: hidden; property to the child?
  5. Did you add the text-overflow: ellipsis; property to the child? (duh)

Hope that helped. Here’s some nice documentation from MDN about the text-overflow property which is well worth the read.

CSS features that Firefox supports but Chrome doesn't

This is a short list of CSS features that work on Firefox but not yet on Chrome. In particular, features that would be really cool to use in production if the other major browsers supported them. Maybe you didn’t know about some of these. Hopefully, I’ll get you informed on them. I’ll update this when the glorious day comes in which we are able to use these without polyfills or any other kind of external libraries.

Scroll snap points

Scroll snap points, in case you haven’t heard of them yet, are a way of introducing precision while scrolling. They’re especially useful for touch devices. Imagine a gallery of images arranged horizontally: a user on a tablet might swipe upwards to continue towards the next image, but the browser scrolls wildly towards the southern ranges of the website. With scroll snap points, we can tell the browser to gracefully stop scrolling in certain points of our document.

There are some cool libraries which implement this with cross-browser compatibility, such as the ever-famous pagePiling.js (which does a lot more things than just scroll snapping), but the native CSS property doesn’t work on Chrome.

CSS scroll snap points work for the horizontal axis as well as for the vertical axis. I’m going to give you an example of a vertical scrolling container with scroll snap points. Hop to Firefox if you’re not there already.

This will only work on Firefox

For a great guide on how to use this, refer to CSS Tricks. The basic syntax you have to use for this is as follows:

.container {
scroll-snap-type: mandatory;
scroll-snap-points-y:repeat(px, vh, vw, percentage);
scroll-snap-destination: x y;
}

Hyphenation

Next up in our CSS features that don’t work on Chrome is hyphenation. Check out this piece of lorem. The upper picture was taken on Chrome, and the lower one was taken on Firefox. They both have hyphenation active, but obviously it only works on Firefox.

Hyphenation in Chrome vs Firefox

The hyphens property is tied to the language attribute you give your HTML, so be sure to use the correct language. Here is the different syntax options you can use in more detail:

.element-that-contains-text {
hyphens: none;
hyphens: manual;
hyphens: auto;
/* And as usual... */
hyphens: inherit;
hyphens: initial;
hyphens: unset;
}

Normally you’d use auto. But the manual option is quite interesting (although not very practical, I think). On manual you’d be able to suggest a line break. This can be done in two different ways: by typing a hyphen (-), which suggests the line break but prints the hyphen even if there’s not going to be a line break, or by adding a soft hyphen (U+00AD). A soft hyphen won’t print but will break the line if able to.

I have recently been informed by a tweet by Michael Scharnagl of a plan to introduce hyphens to Blink, which is interesting. Let’s hope it comes to Chrome soon.

The element function

This feature is awesome! Its effect is a little bit difficult to pick up on. Here’s my attempt at explaining it. The CSS background property accepts several different values, such as colors and image URLs. In Firefox, you can also use the element() function as a value for the background property. Let’s set up two div elements with some simple markup:

<div id='element-on-the-left'>
<!-- whatever content here, this will be
the source for the element() function -->

</div>

<div id='element-on-the-right'>
<!-- here we will print a background
with element() and it will be awesome -->

</div>

Next, we will use this markup to generate a live image of the element on the left. This image will be then used as a background for the element on the right, and the markup goes like this:

#element-on-the-right {
/* set whatever size here and... */
background: -moz-element(#element-on-the-left);
}

The whole thing will end up looking similar to this (here’s a link to codepen.io which obviously only works on Firefox):

element() CSS function demo

Now, at first I thought this was cool, but not extremely useful. Until I saw this post by Vincent de Oliveira. His ideas using this feature are extensive and really nice! Go check it out.

Sticky positioning

Update: This has been added to Chrome in version 56. Hurray!

No idea how this one went past my sight for the original list. Thanks to reddit user Graftak9000, Geoffrey Crofte and Nathan here in the comments for pointing this one out.

Scroll down. This will work on Firefox and (now) Chrome 56+

This sticks to the specified 'top' value without any JS.

This property value solves the issue that many modern websites using as sticky header have. Nowadays, cross-browser implementations of a sticky header (or sidebar, or whatever) effect include JavaScript in one way or another. Elements with this property will behave as a relative positioned element until it reaches a threshold specified by its top property, at which point it will behave as a fixed position element. I guess the demo up there is self-explanatory. Here’s the syntax for sticky elements:

.element {
position: sticky;
top: /* Your value */;
}

Recent versions of Safari also support this but don’t work properly when the parent has overflow: auto; specified. My demo will not work on Safari because it doesn’t include the -webkit- vendor prefix and because it uses said overflow property. Support on Chrome was enabled with a flag on versions 23 through 26 but it was dropped later on. A new implementation is in development, though, so hurray!

Guide to CSS filters

If you’re a web developer, then for one reason or another you’ve probably put your hands (like I have) on image editing software like Photoshop. Also, you’ve probably used the filter menu, which lets you give a layer cool effects such as blur or overlays, and gives you control of contrast, saturation, etc. Well, fear not! Enter CSS filters and say goodbye to the longest minutes of requesting work from our fellow designers: do it yourself! Unlock the powers of the CSS filter property and show the world some magic.

The totally awesome CSS filter property has been around for a while already. Full support was first included in Chrome 18 (March 2012). Firefox adopted it early in version 3.6 but only achieved full support in Firefox 36 (January 2015). A little bit later on, Opera and Safari added support, and nowadays you can use it on most browsers, including the Android native app. Of course, with the exception of cough Internet Explorer (no support) and Microsoft Edge, which includes partial support.

Before actually explaining what any of this does, I’d like to show you a little piece of code I’ve written to let you play around with filters. Go ahead, frolic away:

CSS Filter Playground
Image URL
Opacity
Contrast
Brightness
Saturate
Grayscale
Hue-rotate
Sepia
Invert
Blur
The resulting CSS will appear here.

As you can see, there’s a million things you can do with the CSS filter property. If you haven’t yet, try using a GIF with it. For the lazy ones, here’s a link to a very cool one by Elle Muliarchyk.

CSS filter FAQ


Most of these effects are self-explanatory. But there are some things which may cause a little bit of head scratching. Here’s my attempt at guessing what those are:

Why would I use an opacity filter when I can just use the good old opacity property?

img {
/* A filter... */
filter: opacity(50%);
/* Or normal opacity... */
opacity: 0.5;
}

These two will yield the exact same visual effect. But most modern browsers use hardware acceleration on filters, which improves the performance of opacity filters relative to that of the regular opacity CSS property.

What is hue-rotate? What the hell does it do to my element?

I’ve based this information on this Wikipedia article. Hue is one of the properties of a color. It is described by the CIECAM02 model as “the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow”. Hue is to a color what timbre is to a sound, basically. Each one of the colors in our HTML element can be located (and represented by a degree) on this scale:

Hue scale

When you use, for example:

filter: hue-rotate(20deg);

…you shift every single one of the colors in your HTML element 20 degrees to the right in the scale up there. CSS uses a little bit of a more rudimentary scale though, so what you get is an approximation.

Hue is a cyclical property. Use my filter generator and apply a 360 degree hue-rotate. You’ll see you get the exact same result with a 0 degree hue-rotate, or with no filter at all.

Which different units should I be using with each filter?

For blur, you use pixels. With blur, every pixel is analyzed and the surrounding pixels up to a distance specified by you with:

filter:blur(20px);

…are blended together to create the blur effect.

For hue-rotate, you use degrees. This has already been explained in the last section. For the rest of the filters you use percentages.

More effects Vol. I: drop-shadow

There are two more functions you can do with the CSS filter property other than the ones I’ve included in my little program up there. One of them is an effect very similar to box-shadow. It’s called drop-shadow and the syntax goes as follows:

img {
filter: drop-shadow(16px 16px 10px grey);
}

The values stand for h-shadow v-shadow blur spread color, and the result of the example up there is:

CSS drop-shadow example

But what is the difference between drop-shadow and box-shadow?

Here’s a visual example. That’s the drop-shadow filter on the left and the box-shadow property on the right, on the same image. As you can see, the filter respects the alpha layer on your PNG while the box-shadow property applies the effect on the limits of the canvas. If you were to give an element with a drop-shadow filter a pseudo-element such as :after or :before, the filter would respect that, too.

PNG Example with drop-shadow PNG Example with box-shadow

For a more in-detail comparison, I’m going to link you to a great article by the new code: box-shadow property vs. drop-shadow filter: a complete comparison.

More effects Vol. II: SVG filters

The filters directly available with CSS are no more than a bunch of presets built on top of different definitions of SVG filters (which are essentially XML data). Building these specific filters from zero whenever you wanted to add them would be a PITA, so some awesome people at W3C packed up the presumably more popular filters and created the filter property. This does mean though, that you can still add your own home-brewed SVG filters with the following syntax:

img {
filter: url(#);
}

You can reference on-page anchors by giving your filter an ID and then using that as the URL. If you’d like to go more in-depth on how to create your own filters, check out this article.