add LV_DRAW_UNIT_IDLE

fixes #6374

src/draw/lv_draw.c

@@ -253,7 +253,7 @@ bool lv_draw_dispatch_layer(lv_display_t * disp, lv_layer_t * layer)
         lv_draw_unit_t * u = _draw_info.unit_head;
         while(u) {
             int32_t taken_cnt = u->dispatch_cb(u, layer);
-            if(taken_cnt >= 0) render_running = true;
+            if(taken_cnt != LV_DRAW_UNIT_IDLE) render_running = true;
             u = u->next;
         }
     }

src/draw/lv_draw.h

@@ -27,6 +27,7 @@ extern "C" {
  *      DEFINES
  *********************/
 #define LV_DRAW_UNIT_NONE  0
+#define LV_DRAW_UNIT_IDLE  -1   /*The draw unit is idle, new dispatching might be requested to try again*/
 
 /**********************
  *      TYPEDEFS

src/draw/nxp/pxp/lv_draw_pxp.c

@@ -319,11 +319,11 @@ static int32_t _pxp_dispatch(lv_draw_unit_t * draw_unit, lv_layer_t * layer)
     lv_draw_task_t * t = lv_draw_get_next_available_task(layer, NULL, DRAW_UNIT_ID_PXP);
 
     if(t == NULL || t->preferred_draw_unit_id != DRAW_UNIT_ID_PXP)
-        return -1;
+        return LV_DRAW_UNIT_IDLE;
 
     void * buf = lv_draw_layer_alloc_buf(layer);
     if(buf == NULL)
-        return -1;
+        return LV_DRAW_UNIT_IDLE;
 
     t->state = LV_DRAW_TASK_STATE_IN_PROGRESS;
     draw_pxp_unit->base_unit.target_layer = layer;

src/draw/nxp/vglite/lv_draw_vglite.c

@@ -285,11 +285,11 @@ static int32_t _vglite_dispatch(lv_draw_unit_t * draw_unit, lv_layer_t * layer)
     lv_draw_task_t * t = lv_draw_get_next_available_task(layer, NULL, DRAW_UNIT_ID_VGLITE);
 
     if(t == NULL || t->preferred_draw_unit_id != DRAW_UNIT_ID_VGLITE)
-        return -1;
+        return LV_DRAW_UNIT_IDLE;
 
     void * buf = lv_draw_layer_alloc_buf(layer);
     if(buf == NULL)
-        return -1;
+        return LV_DRAW_UNIT_IDLE;
 
     t->state = LV_DRAW_TASK_STATE_IN_PROGRESS;
     draw_vglite_unit->base_unit.target_layer = layer;

src/draw/renesas/dave2d/lv_draw_dave2d.c

@@ -349,7 +349,6 @@ static int32_t lv_draw_dave2d_dispatch(lv_draw_unit_t * draw_unit, lv_layer_t *
         t = lv_draw_get_next_available_task(layer, NULL, DRAW_UNIT_ID_DAVE2D);
     }
 
-    /* Return 0 is no selection, some tasks can be supported by other units. */
     if(t == NULL) {
 #if  (0 == D2_RENDER_EACH_OPERATION)
         if(false == _lv_ll_is_empty(&_ll_Dave2D_Tasks)) {
@@ -357,13 +356,12 @@ static int32_t lv_draw_dave2d_dispatch(lv_draw_unit_t * draw_unit, lv_layer_t *
             dave2d_execute_dlist_and_flush();
         }
 #endif
-        return 0;
+        return LV_DRAW_UNIT_IDLE;  /*Couldn't start rendering*/
     }
 
-
     void * buf = lv_draw_layer_alloc_buf(layer);
     if(buf == NULL) {
-        return -1;
+        return LV_DRAW_UNIT_IDLE;  /*Couldn't start rendering*/
     }
 
 #if  (0 == D2_RENDER_EACH_OPERATION)

src/draw/sw/lv_draw_sw.c

@@ -372,13 +372,13 @@ static int32_t dispatch(lv_draw_unit_t * draw_unit, lv_layer_t * layer)
     t = lv_draw_get_next_available_task(layer, NULL, DRAW_UNIT_ID_SW);
     if(t == NULL) {
         LV_PROFILER_END;
-        return -1;
+        return LV_DRAW_UNIT_IDLE;  /*Couldn't start rendering*/
     }
 
     void * buf = lv_draw_layer_alloc_buf(layer);
     if(buf == NULL) {
         LV_PROFILER_END;
-        return -1;
+        return LV_DRAW_UNIT_IDLE;  /*Couldn't start rendering*/
     }
 
     t->state = LV_DRAW_TASK_STATE_IN_PROGRESS;

src/draw/vg_lite/lv_draw_vg_lite.c

@@ -172,17 +172,17 @@ static int32_t draw_dispatch(lv_draw_unit_t * draw_unit, lv_layer_t * layer)
     /* Return 0 is no selection, some tasks can be supported by other units. */
     if(!t || t->preferred_draw_unit_id != VG_LITE_DRAW_UNIT_ID) {
         lv_vg_lite_finish(u);
-        return -1;
+        return LV_DRAW_UNIT_IDLE;
     }
 
     /* Return if target buffer format is not supported. */
     if(!lv_vg_lite_is_dest_cf_supported(layer->color_format)) {
-        return -1;
+        return LV_DRAW_UNIT_IDLE;
     }
 
     void * buf = lv_draw_layer_alloc_buf(layer);
     if(!buf) {
-        return -1;
+        return LV_DRAW_UNIT_IDLE;
     }
 
     t->state = LV_DRAW_TASK_STATE_IN_PROGRESS;