RGB Matrix: Custom effects on a kb/user level (#5338)

* Revamped custom effects approach

See docs for example usage

* push-up RGB Matrix default mode

Override default effect using RGB_MATRIX_STARTUP_MODE.
Useful on boards without EEPROM support
(*cough* Massdrop ALT/CTRL *cough*)

* update docs

1 files changed, 50 insertions, 7 deletions

diff --git a/docs/feature_rgb_matrix.md b/docs/feature_rgb_matrix.md
index f2168ab16e..4ce9d15f0f 100644
--- a/docs/feature_rgb_matrix.md
+++ b/docs/feature_rgb_matrix.md
@@ -177,7 +177,7 @@ enum rgb_matrix_effects {
     RGB_MATRIX_GRADIENT_UP_DOWN,    // Static gradient top to bottom, speed controls how much gradient changes
     RGB_MATRIX_BREATHING,           // Single hue brightness cycling animation
     RGB_MATRIX_CYCLE_ALL,           // Full keyboard solid hue cycling through full gradient
-    RGB_MATRIX_CYCLE_LEFT_RIGHT,    // Full gradient scrolling left to right 
+    RGB_MATRIX_CYCLE_LEFT_RIGHT,    // Full gradient scrolling left to right
     RGB_MATRIX_CYCLE_UP_DOWN,       // Full gradient scrolling top to bottom
     RGB_MATRIX_RAINBOW_MOVING_CHEVRON,  // Full gradent Chevron shapped scrolling left to right
     RGB_MATRIX_DUAL_BEACON,         // Full gradient spinning around center of keyboard
@@ -203,7 +203,7 @@ enum rgb_matrix_effects {
     RGB_MATRIX_EFFECT_MAX
 };
 ```
-    
+
 You can disable a single effect by defining `DISABLE_[EFFECT_NAME]` in your `config.h`:
 
 
@@ -236,17 +236,60 @@ You can disable a single effect by defining `DISABLE_[EFFECT_NAME]` in your `con
 |`#define DISABLE_RGB_MATRIX_SOLID_MULTISPLASH`         |Disables `RGB_MATRIX_SOLID_MULTISPLASH`        |
 
 
-## Custom layer effects
+## Custom RGB Matrix Effects
+
+By setting `RGB_MATRIX_CUSTOM_USER` (and/or `RGB_MATRIX_CUSTOM_KB`) in `rule.mk`, new effects can be defined directly from userspace, without having to edit any QMK core files.
+
+To declare new effects, create a new `rgb_matrix_user/kb.inc` that looks something like this:
 
-Custom layer effects can be done by defining this in your `<keyboard>.c`:
+`rgb_matrix_user.inc` should go in the root of the keymap directory.
+`rgb_matrix_kb.inc` should go in the root of the keyboard directory.
 
 ```C
-void rgb_matrix_indicators_kb(void) {
-    rgb_matrix_set_color(index, red, green, blue);
+// !!! DO NOT ADD #pragma once !!! //
+
+// Step 1.
+// Declare custom effects using the RGB_MATRIX_EFFECT macro
+// (note the lack of semicolon after the macro!)
+RGB_MATRIX_EFFECT(my_cool_effect)
+RGB_MATRIX_EFFECT(my_cool_effect2)
+
+// Step 2.
+// Define effects inside the `RGB_MATRIX_CUSTOM_EFFECT_IMPLS` ifdef block
+#ifdef RGB_MATRIX_CUSTOM_EFFECT_IMPLS
+
+// e.g: A simple effect, self-contained within a single method
+static bool my_cool_effect(effect_params_t* params) {
+  RGB_MATRIX_USE_LIMITS(led_min, led_max);
+  for (uint8_t i = led_min; i < led_max; i++) {
+    rgb_matrix_set_color(i, 0xff, 0xff, 0x00);
+  }
+  return led_max < DRIVER_LED_TOTAL;
+}
+
+// e.g: A more complex effect, relying on external methods and state, with
+// dedicated init and run methods
+static uint8_t some_global_state;
+static void my_cool_effect2_complex_init(effect_params_t* params) {
+  some_global_state = 1;
 }
+static bool my_cool_effect2_complex_run(effect_params_t* params) {
+  RGB_MATRIX_USE_LIMITS(led_min, led_max);
+  for (uint8_t i = led_min; i < led_max; i++) {
+    rgb_matrix_set_color(i, 0xff, some_global_state++, 0xff);
+  }
+
+  return led_max < DRIVER_LED_TOTAL;
+}
+static bool my_cool_effect2(effect_params_t* params) {
+  if (params->init) my_cool_effect2_complex_init(params);
+  return my_cool_effect2_complex_run(params);
+}
+
+#endif // RGB_MATRIX_CUSTOM_EFFECT_IMPLS
 ```
 
-A similar function works in the keymap as `rgb_matrix_indicators_user`.
+For inspiration and examples, check out the built-in effects under `quantum/rgb_matrix_animation/`
 
 
 ## Colors