feat(underglow): Add support for configurable min/max brightness

Co-authored-by: jrhrsmit <jasper.770@gmail.com>

app/Kconfig

@@ -262,6 +262,16 @@ config ZMK_RGB_UNDERGLOW_EXT_POWER
 	bool "RGB underglow toggling also controls external power"
 	default y
 
+config ZMK_RGB_UNDERGLOW_BRT_MIN
+	int "RGB underglow minimum brightness in percent"
+	range 0 100
+	default 0
+
+config ZMK_RGB_UNDERGLOW_BRT_MAX
+	int "RGB underglow maximum brightness in percent"
+	range 0 100
+	default 100
+
 config ZMK_RGB_UNDERGLOW_HUE_STEP
 	int "RGB underglow hue step in degrees of 360"
 	default 10

app/src/rgb_underglow.c

@@ -28,6 +28,9 @@ LOG_MODULE_DECLARE(zmk, CONFIG_ZMK_LOG_LEVEL);
 #define SAT_MAX 100
 #define BRT_MAX 100
 
+BUILD_ASSERT(CONFIG_ZMK_RGB_UNDERGLOW_BRT_MIN <= CONFIG_ZMK_RGB_UNDERGLOW_BRT_MAX,
+    "ERROR: RGB underglow maximum brightness is less than minimum brightness");
+
 enum rgb_underglow_effect {
     UNDERGLOW_EFFECT_SOLID,
     UNDERGLOW_EFFECT_BREATHE,
@@ -54,6 +57,17 @@ static struct rgb_underglow_state state;
 static const struct device *ext_power;
 #endif
 
+static struct zmk_led_hsb hsb_scale_min_max(struct zmk_led_hsb hsb) {
+    hsb.b = CONFIG_ZMK_RGB_UNDERGLOW_BRT_MIN +
+        (CONFIG_ZMK_RGB_UNDERGLOW_BRT_MAX - CONFIG_ZMK_RGB_UNDERGLOW_BRT_MIN) * hsb.b / BRT_MAX;
+    return hsb;
+}
+
+static struct zmk_led_hsb hsb_scale_zero_max(struct zmk_led_hsb hsb) {
+    hsb.b = hsb.b * CONFIG_ZMK_RGB_UNDERGLOW_BRT_MAX / BRT_MAX;
+    return hsb;
+}
+
 static struct led_rgb hsb_to_rgb(struct zmk_led_hsb hsb) {
     double r, g, b;
 
@@ -105,7 +119,7 @@ static struct led_rgb hsb_to_rgb(struct zmk_led_hsb hsb) {
 
 static void zmk_rgb_underglow_effect_solid() {
     for (int i = 0; i < STRIP_NUM_PIXELS; i++) {
-        pixels[i] = hsb_to_rgb(state.color);
+        pixels[i] = hsb_to_rgb(hsb_scale_min_max(state.color));
     }
 }
 
@@ -114,7 +128,7 @@ static void zmk_rgb_underglow_effect_breathe() {
         struct zmk_led_hsb hsb = state.color;
         hsb.b = abs(state.animation_step - 1200) / 12;
 
-        pixels[i] = hsb_to_rgb(hsb);
+        pixels[i] = hsb_to_rgb(hsb_scale_zero_max(hsb));
     }
 
     state.animation_step += state.animation_speed * 10;
@@ -129,7 +143,7 @@ static void zmk_rgb_underglow_effect_spectrum() {
         struct zmk_led_hsb hsb = state.color;
         hsb.h = state.animation_step;
 
-        pixels[i] = hsb_to_rgb(hsb);
+        pixels[i] = hsb_to_rgb(hsb_scale_min_max(hsb));
     }
 
     state.animation_step += state.animation_speed;
@@ -141,7 +155,7 @@ static void zmk_rgb_underglow_effect_swirl() {
         struct zmk_led_hsb hsb = state.color;
         hsb.h = (HUE_MAX / STRIP_NUM_PIXELS * i + state.animation_step) % HUE_MAX;
 
-        pixels[i] = hsb_to_rgb(hsb);
+        pixels[i] = hsb_to_rgb(hsb_scale_min_max(hsb));
     }
 
     state.animation_step += state.animation_speed * 2;
@@ -371,12 +385,7 @@ struct zmk_led_hsb zmk_rgb_underglow_calc_brt(int direction) {
     struct zmk_led_hsb color = state.color;
 
     int b = color.b + (direction * CONFIG_ZMK_RGB_UNDERGLOW_BRT_STEP);
-    if (b < 0) {
-        b = 0;
-    } else if (b > BRT_MAX) {
-        b = BRT_MAX;
-    }
-    color.b = b;
+    color.b = CLAMP(b, 0, BRT_MAX);
 
     return color;
 }