When a full screen refresh is done, apply a vertical scroll during the refresh. This makes the transition from one screen the another one smoother, even if the refresh rate is slow.

src/DisplayApp/DisplayApp.cpp

@@ -117,19 +117,19 @@ void DisplayApp::Refresh() {
         OnTouchEvent();
         break;
       case Messages::ButtonPushed:
-        if(!currentScreen->OnButtonPushed()) {
-          systemTask.PushMessage(System::SystemTask::Messages::GoToSleep);
-        }
-//        currentScreen.reset(nullptr);
-//        if(toggle) {
-//          modal.Show();
-////          currentScreen.reset(new Screens::Tile(this));
-//          toggle = false;
-//        } else {
-//          modal.Hide();
-////          currentScreen.reset(new Screens::Clock(this, dateTimeController, batteryController, bleController));
-//          toggle = true;
+//        if(!currentScreen->OnButtonPushed()) {
+//          systemTask.PushMessage(System::SystemTask::Messages::GoToSleep);
 //        }
+        lvgl.SetFullRefresh();
+        lv_disp_set_direction(lv_disp_get_default(), 0);
+        currentScreen.reset(nullptr);
+        if(toggle) {
+          currentScreen.reset(new Screens::Tile(this));
+          toggle = false;
+        } else {
+          currentScreen.reset(new Screens::Clock(this, dateTimeController, batteryController, bleController));
+          toggle = true;
+        }
 
         break;
     }
@@ -140,6 +140,7 @@ void DisplayApp::RunningState() {
 //  clockScreen.SetCurrentDateTime(dateTimeController.CurrentDateTime());
 
   if(!currentScreen->Refresh()) {
+    lvgl.SetFullRefresh();
     currentScreen.reset(nullptr);
     switch(nextApp) {
       case Apps::None:

src/DisplayApp/LittleVgl.cpp

@@ -64,21 +64,95 @@ void LittleVgl::InitTouchpad() {
   lv_indev_drv_register(&indev_drv);
 }
 
+void LittleVgl::SetFullRefresh() {
+  fullRefresh = true;
+}
+
 void LittleVgl::FlushDisplay(const lv_area_t *area, lv_color_t *color_p) {
   ulTaskNotifyTake(pdTRUE, 500);
 
-  auto x = area->x1;
-  auto y = area->y1;
-  auto width = (area->x2-area->x1)+1;
-  auto height = (area->y2-area->y1)+1;
-  lcd.BeginDrawBuffer(x, y, width, height);
-  lcd.NextDrawBuffer(reinterpret_cast<const uint8_t *>(color_p), width * height*2) ;
+  // TODO refactore and remove duplicated code
+
+  uint16_t x, y, y1, y2, width, height = 0;
+  if(fullRefresh) {
+    if(scrollDirection == LittleVgl::ScrollDirections::Down) {
+      if(area->y2 == visibleNbLines-1) {
+        writeOffset = ((writeOffset + totalNbLines) - visibleNbLines) % totalNbLines;
+      }
+      x = area->x1;
+      width = (area->x2 - area->x1) + 1;
+
+      y1 = (area->y1 + writeOffset) % totalNbLines;
+      y2 = (area->y2 + writeOffset) % totalNbLines;
+      y = y1;
+      height = (y2 - y1) + 1;
+
+      if(area->y2 < visibleNbLines - 1) {
+        uint16_t toScroll = 0;
+        if(area->y1 == 0) {
+          toScroll = height*2;
+          fullRefresh = false;
+          lv_disp_set_direction(lv_disp_get_default(), 0);
+        } else {
+          toScroll = height;
+        }
+
+        if(scrollOffset >= toScroll)
+          scrollOffset -= toScroll;
+        else {
+          toScroll -= scrollOffset;
+          scrollOffset = (totalNbLines) - toScroll;
+        }
+
+        lcd.VerticalScrollDefinition(0, 320, 0);
+        lcd.VerticalScrollStartAddress(scrollOffset);
+      }
+
+      lcd.BeginDrawBuffer(x, y, width, height);
+      lcd.NextDrawBuffer(reinterpret_cast<const uint8_t *>(color_p), width * height*2) ;
+
+    } else {
+      if(area->y1 == 0) {
+        writeOffset = (writeOffset + visibleNbLines) % totalNbLines;
+      }
+
+      x = area->x1;
+      width = (area->x2 - area->x1) + 1;
+
+      y1 = (area->y1 + writeOffset) % totalNbLines;
+      y2 = (area->y2 + writeOffset) % totalNbLines;
+      y = y1;
+      height = (y2 - y1) + 1;
+
+      if(area->y1 > 0) {
+        if(area->y2 == visibleNbLines -1) {
+          scrollOffset += (height * 2);
+          fullRefresh = false;
+          lv_disp_set_direction(lv_disp_get_default(), 0);
+        } else {
+          scrollOffset += height;
+        }
+        scrollOffset = scrollOffset % totalNbLines;
+        lcd.VerticalScrollDefinition(0, 320, 0);
+        lcd.VerticalScrollStartAddress(scrollOffset);
+      }
+
+      lcd.BeginDrawBuffer(x, y, width, height);
+      lcd.NextDrawBuffer(reinterpret_cast<const uint8_t *>(color_p), width * height*2);
+    }
+  } else {
+    x = area->x1;
+    y = area->y1;
+    width = (area->x2 - area->x1) + 1;
+    height = (area->y2 - area->y1) + 1;
+    lcd.BeginDrawBuffer(x, y, width, height);
+    lcd.NextDrawBuffer(reinterpret_cast<const uint8_t *>(color_p), width * height*2) ;
+  }
 
   /* IMPORTANT!!!
    * Inform the graphics library that you are ready with the flushing*/
   lv_disp_flush_ready(&disp_drv);
 }
-
 bool LittleVgl::GetTouchPadInfo(lv_indev_data_t *ptr) {
   auto info = touchPanel.GetTouchInfo();
 
@@ -715,3 +789,4 @@ void LittleVgl::InitThemeWindow() {
 //  theme.style.win.btn.rel = &lv_style_transp;
 //  theme.style.win.btn.pr  = &win_btn_pr;
 }
+

src/DisplayApp/LittleVgl.h

@@ -15,10 +15,15 @@ namespace Pinetime {
     class LittleVgl {
       public:
         LittleVgl(Pinetime::Drivers::St7789& lcd, Pinetime::Drivers::Cst816S& touchPanel);
+
+        LittleVgl(const LittleVgl&) = delete;
+        LittleVgl& operator=(const LittleVgl&) = delete;
+        LittleVgl(LittleVgl&&) = delete;
+        LittleVgl& operator=(LittleVgl&&) = delete;
+
         void FlushDisplay(const lv_area_t * area, lv_color_t * color_p);
-
-
         bool GetTouchPadInfo(lv_indev_data_t *ptr);
+        void SetFullRefresh();
       private:
         void InitDisplay();
         void InitTouchpad();
@@ -94,6 +99,15 @@ namespace Pinetime {
         lv_style_t win_btn_pr;
 
         bool firstTouch = true;
+        bool fullRefresh = false;
+        static constexpr uint8_t nbWriteLines = 4;
+        static constexpr uint16_t totalNbLines = 320;
+        static constexpr uint16_t visibleNbLines = 240;
+        static constexpr uint8_t MaxScrollOffset() { return LV_VER_RES_MAX - nbWriteLines; }
+        enum class ScrollDirections {Unknown, Up, Down};
+        ScrollDirections scrollDirection = ScrollDirections::Up;
+        uint16_t writeOffset = 0;
+        uint16_t scrollOffset = 0;
     };
   }
 }