reactive backlighting for QMK

make your custom mechanical keyboard's keys light up when pressed

Recently, I picked up a new mechanical keyboard PCB (an HS60). It’s nice, it even has addressable LEDs under each key.

I didn’t like any of the stock LED pattern options. My thoughts were:

  • I want keys to only light up when I press them
  • They should fade out nicely
  • I’ve seen this behaviour on pre-built keyboards before, why isn’t it in the stock wilba_tech RGB matrix interface?

So, obviously, I did some patching.

First off, we need to get our own RGB backlighting effect to be called:

@@ -1928,6 +1930,9 @@ static void gpt_backlight_timer_task(GPTDriver *gptp)
     case 10:
+    case 11:
+      backlight_effect_user();
+      break;

Then, we need to actually define this new backlight_effect_user for that file.

Above, I stuck a simple relative #include directive to point back to my own repository that is sub-tree-ed into the QMK sources:

+#include "../hs60/v2/iso/keymaps/half-kh-hacker/backlighting.h"

And in that header file, I simply define my desired backlighting behaviour:

#pragma once

void backlight_effect_user(void) {
  for (int i = 0; i < BACKLIGHT_LED_COUNT; i++) {
    HSV hsv = { .h = 0, .s = 0, .v = 255 - g_key_hit[i] };
    RGB rgb = hsv_to_rgb(hsv);
    backlight_set_color(i, rgb.r, rgb.g, rgb.b);

Obviously, you can set the HSV values to whatever you want, and probably multiply the value you get from g_key_hit - The key_hit value is a uint8_t of number of twentieths of a second, so with the snippet above it takes almost 13(!) seconds to fully fade out a key.