Update Raindrops effect to respect LED range limits (#24531)

quantum/rgb_matrix/animations/raindrops_anim.h

@@ -2,35 +2,42 @@
 RGB_MATRIX_EFFECT(RAINDROPS)
 #    ifdef RGB_MATRIX_CUSTOM_EFFECT_IMPLS
 
-static void raindrops_set_color(int i, effect_params_t* params) {
+static void raindrops_set_color(uint8_t i, effect_params_t* params) {
     if (!HAS_ANY_FLAGS(g_led_config.flags[i], params->flags)) return;
-    hsv_t hsv = {0, rgb_matrix_config.hsv.s, rgb_matrix_config.hsv.v};
+    hsv_t hsv = rgb_matrix_config.hsv;
 
     // Take the shortest path between hues
-    int16_t deltaH = ((rgb_matrix_config.hsv.h + 180) % 360 - rgb_matrix_config.hsv.h) / 4;
+    int16_t deltaH = ((hsv.h + 180) % 360 - hsv.h) / 4;
     if (deltaH > 127) {
         deltaH -= 256;
     } else if (deltaH < -127) {
         deltaH += 256;
     }
 
-    hsv.h     = rgb_matrix_config.hsv.h + (deltaH * (random8() & 0x03));
+    hsv.h += (deltaH * random8_max(3));
     rgb_t rgb = rgb_matrix_hsv_to_rgb(hsv);
     rgb_matrix_set_color(i, rgb.r, rgb.g, rgb.b);
 }
 
 bool RAINDROPS(effect_params_t* params) {
+    static uint16_t index = RGB_MATRIX_LED_COUNT + 1;
+
+    // Periodic trigger for LED change
+    if ((params->iter == 0) && (scale16by8(g_rgb_timer, qadd8(rgb_matrix_config.speed, 16)) % 10 == 0)) {
+        index = random8_max(RGB_MATRIX_LED_COUNT);
+    }
+
     RGB_MATRIX_USE_LIMITS(led_min, led_max);
-    if (!params->init) {
-        // Change one LED every tick, make sure speed is not 0
-        if (scale16by8(g_rgb_timer, qadd8(rgb_matrix_config.speed, 16)) % 10 == 0) {
-            raindrops_set_color(random8_max(RGB_MATRIX_LED_COUNT), params);
-        }
-    } else {
-        for (int i = led_min; i < led_max; i++) {
+    if (params->init) {
+        for (uint8_t i = led_min; i < led_max; i++) {
             raindrops_set_color(i, params);
         }
     }
+    // Change LED once and set index out of range till next trigger
+    else if (led_min <= index && index < led_max) {
+        raindrops_set_color(index, params);
+        index = RGB_MATRIX_LED_COUNT + 1;
+    }
     return rgb_matrix_check_finished_leds(led_max);
 }