Enable LVGL double buffering and improve border redraw

Introduces a second LVGL buffer for double buffering to reduce display tearing. Updates critical border flashing logic to invalidate and immediately refresh the border area, ensuring cleaner redraws and minimizing visual artifacts.

Author: zjwhitehead

inc/sp140/lvgl/lvgl_core.h

@@ -24,6 +24,7 @@ extern int8_t displayCS;  // Display chip select pin
 extern lv_disp_drv_t disp_drv;
 extern lv_disp_draw_buf_t draw_buf;
 extern lv_color_t buf[LVGL_BUFFER_SIZE];
+extern lv_color_t buf2[LVGL_BUFFER_SIZE];  // Second buffer for double buffering
 extern Adafruit_ST7735* tft_driver;
 extern uint32_t lvgl_last_update;
 // Shared SPI bus mutex (guards TFT + MCP2515 access)

src/sp140/lvgl/lvgl_core.cpp

@@ -7,6 +7,7 @@
 lv_disp_drv_t disp_drv;
 lv_disp_draw_buf_t draw_buf;
 lv_color_t buf[LVGL_BUFFER_SIZE];
+lv_color_t buf2[LVGL_BUFFER_SIZE];  // Second buffer for double buffering
 Adafruit_ST7735* tft_driver = nullptr;
 uint32_t lvgl_last_update = 0;
 // Define the shared SPI bus mutex
@@ -18,10 +19,10 @@ void setupLvglBuffer() {
   lv_init();
   USBSerial.println("LVGL initialized");
 
-  // Setup buffer for LVGL
-  USBSerial.println("Setting up LVGL buffer");
-  lv_disp_draw_buf_init(&draw_buf, buf, NULL, LVGL_BUFFER_SIZE);
-  USBSerial.println("LVGL buffer initialized");
+  // Setup double buffer for LVGL to reduce tearing
+  USBSerial.println("Setting up LVGL double buffer");
+  lv_disp_draw_buf_init(&draw_buf, buf, buf2, LVGL_BUFFER_SIZE);
+  USBSerial.println("LVGL double buffer initialized");
 }
 
 void setupLvglDisplay(

src/sp140/lvgl/lvgl_updates.cpp

@@ -183,16 +183,22 @@ static void critical_border_flash_timer_cb(lv_timer_t* timer) {
     bool is_on = !lv_obj_has_flag(critical_border, LV_OBJ_FLAG_HIDDEN);
     if (is_on) {
       lv_obj_add_flag(critical_border, LV_OBJ_FLAG_HIDDEN);
+      // Invalidate the border area to ensure clean redraw
+      lv_obj_invalidate(critical_border);
       lv_timer_set_period(timer, 700); // Off duration
     } else {
       lv_obj_clear_flag(critical_border, LV_OBJ_FLAG_HIDDEN);
+      // Invalidate the border area to ensure clean redraw
+      lv_obj_invalidate(critical_border);
       lv_timer_set_period(timer, 300); // On duration
 
       // Trigger vibration pulse in sync with border "on"
       if (ENABLE_VIBE) {
         pulseVibration(300, 200); // 300ms pulse, intensity 200
       }
     }
+    // Force immediate refresh to minimize tearing
+    lv_refr_now(lv_disp_get_default());
   }
 }
 
@@ -230,7 +236,10 @@ void startCriticalBorderFlashDirect() {
   if (critical_border != NULL && !isFlashingCriticalBorder) {
     isFlashingCriticalBorder = true;
     lv_obj_clear_flag(critical_border, LV_OBJ_FLAG_HIDDEN); // Start visible
+    lv_obj_invalidate(critical_border); // Ensure clean initial draw
     critical_border_flash_timer = lv_timer_create(critical_border_flash_timer_cb, 300, NULL);
+    // Force immediate refresh for clean start
+    lv_refr_now(lv_disp_get_default());
   }
 }
 
@@ -241,6 +250,9 @@ void stopCriticalBorderFlashDirect() {
   }
   if (critical_border != NULL) {
     lv_obj_add_flag(critical_border, LV_OBJ_FLAG_HIDDEN);
+    lv_obj_invalidate(critical_border); // Ensure clean removal
+    // Force immediate refresh for clean stop
+    lv_refr_now(lv_disp_get_default());
   }
   isFlashingCriticalBorder = false;
 }