Customize Emacs Mode Line Color Based On Window Count

Introduction

Hey guys! Ever felt like your Emacs mode line is a bit too… enthusiastic? You know, all bright and colorful even when you've only got one or two windows open? Yeah, me too. I've been wrestling with this issue of a coloured active mode line for a while now. I love the visual distinction it provides, making it super easy to spot the active window amidst a sea of buffers. But let's be real, sometimes it's just overkill. I mean, if I've only got a couple of windows open, the colourful mode line feels a bit like a spotlight on a stage with only one actor. It's distracting, not helpful. So, I started thinking, wouldn't it be awesome if we could reserve that vibrant active mode line for when things really get busy? You know, when you're juggling multiple projects, editing files across different directories, and basically living the Emacs dream (or nightmare, depending on your perspective)? That's when a distinctive mode line becomes a lifesaver, a quick visual cue to keep you oriented in the Emacs-verse. This led me down a rabbit hole of Emacs Lisp customization, and I'm excited to share what I've learned with you all. We're going to dive deep into how to make your mode line smarter, more context-aware, and ultimately, more helpful. We'll explore the code snippets, the logic behind them, and how you can adapt them to your own Emacs setup. So, buckle up, grab your favourite beverage, and let's get started on this journey to a more intelligent and less visually noisy Emacs experience! This article will walk you through how to configure Emacs to display a coloured active mode line only when you have a certain number of windows open. This approach helps to reduce visual clutter when you're working with fewer windows while still providing a clear visual distinction when things get busy.

The Problem: Overly Enthusiastic Mode Lines

Okay, let's break down the core issue we're tackling here. The default behavior of Emacs, and even many customized Emacs setups, is to have a consistently coloured active mode line. Now, don't get me wrong, I appreciate the intention behind this. A coloured mode line is fantastic for quickly identifying the active window, especially when you're dealing with a multitude of buffers and windows. It's like a beacon in the Emacs wilderness, guiding your eyes to the right place. However, the problem arises when this enthusiasm becomes… well, a bit much. Imagine this: you're working on a simple task, maybe editing a single file or writing a quick email. You've got two windows open, neatly arranged. In this scenario, a brightly coloured active mode line feels almost like a shout, when a gentle whisper would suffice. It's visually distracting and, frankly, a bit unnecessary. The colourful mode line, in this case, doesn't add much value. It's like wearing a tuxedo to a casual brunch – technically correct, but definitely overkill. This constant colourful mode line can also contribute to visual fatigue, especially during long coding sessions. Your eyes are constantly drawn to the bright colours, even when you don't need them to be. It's like having a notification light flashing incessantly, even when there's nothing new to see. This is where the idea of a context-aware mode line comes in. What if our active mode line could intelligently adapt to the situation? What if it could dim its colours when we're working with fewer windows and brighten up only when we're juggling multiple tasks? That's the kind of nuanced, user-friendly experience we're aiming for. We want our coloured mode line to be a helpful tool, not a visual distraction. So, how do we achieve this? That's what we'll explore in the following sections. We'll delve into the Emacs Lisp code required to make this magic happen, breaking down each step and explaining the logic behind it. By the end of this article, you'll have the knowledge and tools to create a more intelligent and context-aware mode line, one that's there to help you, not to shout at you.

The Solution: Conditional Colouring

The core idea behind our solution is to make the coloured active mode line conditional. Instead of always displaying a coloured mode line, we'll set up Emacs to check the number of open windows. If the number exceeds a certain threshold, say, three or four, then we'll activate the colours. Otherwise, we'll use a more subdued mode line, perhaps with a simple background colour or no special colouring at all. This approach allows us to reserve the colourful mode line for situations where it's genuinely helpful, reducing visual clutter in simpler scenarios. The implementation involves a bit of Emacs Lisp, but don't worry, we'll break it down step by step. We'll need to define a function that checks the number of windows and then modifies the mode-line-face accordingly. The mode-line-face is the face (Emacs's term for a set of display attributes like colour, font, and weight) that's used for the active mode line. By modifying this face, we can control the appearance of the mode line. First, we'll define a variable to store the threshold number of windows. This allows us to easily adjust the threshold without having to modify the code directly. Then, we'll create the function that checks the window count and sets the mode-line-face. This function will use the window-list function to get a list of all windows and then check the length of that list. If the length is greater than or equal to our threshold, we'll set the mode-line-face to a coloured face. Otherwise, we'll set it to a more subdued face. Finally, we'll need to tell Emacs to run this function whenever the window configuration changes. We can do this using a hook. A hook is a function that Emacs runs automatically when a certain event occurs. In this case, we'll use the window-configuration-change-hook, which is run whenever the window configuration is changed (e.g., when a new window is opened or closed). By adding our function to this hook, we ensure that the mode line is updated whenever the window configuration changes. This ensures that our conditional colouring logic is always up-to-date, providing a seamless and context-aware user experience. In the next sections, we'll dive into the specific code snippets and explain how they work in detail. We'll also discuss how to customize the colours and the threshold to suit your own preferences and workflow.

Implementing the Solution: Code Snippets and Explanation

Alright, let's get our hands dirty with some Emacs Lisp! This is where the rubber meets the road, and we'll transform our ideas into actual code. Don't worry if you're not a Lisp guru; I'll walk you through each step, explaining the logic behind the code. First, we need to define a variable to store our window threshold. This is the number of windows that must be open before the coloured mode line kicks in. Let's set it to 3 for now, but you can adjust it to your liking. We'll use the defvar macro to define a new variable called my-mode-line-colour-threshold.

(defvar my-mode-line-colour-threshold 3
  "Number of windows before coloured mode line is activated.")

This code snippet defines a variable named my-mode-line-colour-threshold and sets its initial value to 3. The string after the value is a documentation string, which is helpful for understanding the purpose of the variable. Now, let's define the function that checks the window count and sets the mode-line-face. We'll call this function my-update-mode-line-colour.

(defun my-update-mode-line-colour ()
  (let ((window-count (length (window-list))))
    (if (>= window-count my-mode-line-colour-threshold)
        (set-face-attribute 'mode-line nil :background "darkseagreen" :foreground "black" :box '(:line-width 2 :color "grey"))
      (set-face-attribute 'mode-line nil :background "grey30" :foreground "white"))))

Let's break this down. The defun macro defines a new function called my-update-mode-line-colour. Inside the function, we use let to create a local variable called window-count. We set this variable to the number of windows by using the length function on the result of the window-list function. The window-list function returns a list of all windows, and length returns the number of elements in that list. Next, we use an if statement to check if the window-count is greater than or equal to our my-mode-line-colour-threshold. If it is, we set the mode-line-face to a coloured face using the set-face-attribute function. We set the background colour to "darkseagreen", the foreground colour to "black", and add a grey box around the mode line. If the window-count is less than the threshold, we set the mode-line-face to a more subdued face with a grey background and white foreground. You can customize these colours to your liking. Feel free to experiment with different colour combinations to find what works best for you. Finally, we need to add this function to the window-configuration-change-hook. This will ensure that the function is run whenever the window configuration changes.

(add-hook 'window-configuration-change-hook 'my-update-mode-line-colour)

This code snippet uses the add-hook function to add our my-update-mode-line-colour function to the window-configuration-change-hook. Now, whenever the window configuration changes, our function will be run, and the mode line will be updated accordingly. To make these changes take effect, you'll need to evaluate the code. You can do this by copying the code into your Emacs configuration file (usually ~/.emacs or ~/.emacs.d/init.el) and then reloading the configuration (by evaluating (load-file "~/.emacs.d/init.el") or restarting Emacs). Alternatively, you can evaluate each code snippet individually by placing your cursor at the end of the snippet and pressing C-x C-e (that's Ctrl-x followed by Ctrl-e). Once you've evaluated the code, you should see the mode line change as you open and close windows. If you open more than three windows, the mode line should become coloured. If you close windows until you have fewer than three, the mode line should revert to the subdued grey. Congratulations! You've successfully implemented conditional mode line colouring in Emacs. In the next section, we'll explore some customizations and further enhancements.

Customization and Further Enhancements

The beauty of Emacs is its customizability, and our conditional mode line setup is no exception. There are several ways we can tweak and enhance this setup to better suit our individual preferences and workflows. First and foremost, let's talk about colours. The colours I've chosen – darkseagreen for the active mode line and grey30 for the inactive one – are just starting points. You might prefer a different colour scheme altogether. The set-face-attribute function gives you a lot of flexibility in this regard. You can specify colours by name (like "darkseagreen" or "black"), by hexadecimal code (like "#RRGGBB"), or even by RGB values. Experiment with different colours to find a combination that you find visually appealing and easy on the eyes. Consider using a colour palette generator or a website that specializes in accessible colour combinations to ensure good contrast and readability. You can also customize the other attributes of the mode-line-face, such as the font, font size, and font weight. For example, you could make the active mode line bold or use a larger font size to make it even more prominent. Another customization option is the threshold number of windows. We've set it to 3, but you might find that a different value works better for you. If you tend to work with many windows open, you might want to increase the threshold. If you prefer a more subtle mode line, you might want to decrease it. You can easily change the value of the my-mode-line-colour-threshold variable to adjust the threshold. Beyond simple colour and threshold adjustments, we can also add more sophisticated logic to our conditional mode line. For example, we could consider the size of the windows in addition to the number of windows. If we have three small windows open, we might not want the coloured mode line to activate. We could also consider the current major mode. For example, we might want a coloured mode line only when we're in a programming mode, like python-mode or java-mode. To implement these more advanced customizations, we'll need to modify our my-update-mode-line-colour function. We can add more conditions to the if statement to check for window size and major mode. For example, to check the size of the windows, we can use the window-width and window-height functions. To check the major mode, we can use the major-mode variable. We can also use other faces for mode line display. For example, you may want to change mode-line-inactive-face too. By combining these techniques, we can create a truly intelligent and context-aware mode line, one that adapts to our workflow and provides the right level of visual cues at the right time. In the final section, we'll discuss some best practices and troubleshooting tips.

Best Practices and Troubleshooting Tips

Before we wrap things up, let's talk about some best practices and troubleshooting tips to ensure that your conditional mode line setup runs smoothly and remains maintainable. First and foremost, always back up your Emacs configuration file before making any significant changes. This is a general best practice for any Emacs customization, but it's especially important when you're working with Lisp code. If something goes wrong, you can always revert to your backup. When you're writing Emacs Lisp code, it's crucial to indent your code properly. Proper indentation makes your code much easier to read and understand, both for yourself and for others. Emacs has built-in support for Lisp indentation, so take advantage of it. Use the indent-for-comment command (usually bound to M-;) to automatically indent your code. Comments are also essential for maintainability. Add comments to your code to explain what it does and why you've made certain choices. This will make it much easier to understand your code later, especially if you haven't looked at it in a while. When you're debugging Emacs Lisp code, the *Messages* buffer is your best friend. This buffer contains all the error messages and other output from Emacs. If you're experiencing problems with your conditional mode line, check the *Messages* buffer for any error messages. The edebug package is a powerful debugging tool for Emacs Lisp. It allows you to step through your code line by line, inspect variables, and see exactly what's happening. If you're having trouble debugging your code, consider using edebug. If your conditional mode line isn't working as expected, the first thing to do is to check that you've evaluated the code correctly. Make sure you've copied the code into your Emacs configuration file and reloaded the configuration, or that you've evaluated each code snippet individually using C-x C-e. If the code is evaluated correctly, double-check your logic. Make sure the threshold is set to the value you expect, and that the conditions in your if statement are correct. Use the message function to print the values of variables to the *Messages* buffer. This can be helpful for understanding what's happening in your code. For example, you could add a (message "Window count: %d" window-count) line to your my-update-mode-line-colour function to see the current window count. Finally, remember that Emacs is a vast and complex system, and there's always more to learn. Don't be afraid to experiment, explore, and ask for help. The Emacs community is incredibly supportive and helpful, and there are many resources available online, including the Emacs manual, the Emacs Wiki, and various forums and mailing lists. By following these best practices and troubleshooting tips, you can ensure that your conditional mode line setup remains a valuable and reliable part of your Emacs workflow.

Conclusion

We've reached the end of our journey into the world of conditional mode line colouring in Emacs. We've explored the problem of overly enthusiastic mode lines, devised a solution based on conditional logic, implemented the solution with Emacs Lisp code, and discussed various customization and enhancement options. We've also covered best practices and troubleshooting tips to ensure that your setup remains robust and maintainable. By now, you should have a solid understanding of how to create a mode line that adapts to your workflow, providing visual cues when you need them and staying out of your way when you don't. This is just one example of the power and flexibility of Emacs. By customizing your Emacs environment, you can create a tool that perfectly fits your needs and preferences. Don't be afraid to experiment with different customizations and explore the vast ecosystem of Emacs packages and extensions. The more you customize Emacs, the more efficient and enjoyable your editing experience will become. I hope this article has been helpful and inspiring. If you have any questions or comments, feel free to leave them below. And remember, happy hacking!