fix(obj): style opa of other part is not effective (#7905)

Signed-off-by: yushuailong <yushuailong1@xiaomi.com>
Signed-off-by: yushuailong1 <yushuailong1@xiaomi.com>
Co-authored-by: yushuailong1 <yushuailong1@xiaomi.com>

src/core/lv_obj_draw.c

@@ -379,7 +379,11 @@ static inline lv_opa_t get_layer_opa(const lv_obj_t * obj, lv_part_t part, const
 {
     if(base_dsc->layer) {
         /* Accessing the layer opa directly is faster than using get style opa recursive */
-        return base_dsc->layer->opa;
+        if(part == LV_PART_MAIN) {
+            return base_dsc->layer->opa;
+        }
+
+        return LV_OPA_MIX2(base_dsc->layer->opa, lv_obj_get_style_opa(obj, part));
     }
 
     /* fallback to old recursive style opa */

tests/src/test_cases/widgets/test_checkbox.c

@@ -24,6 +24,17 @@ static void event_handler(lv_event_t * e)
     }
 }
 
+void setUp(void)
+{
+    /* Function run before every test */
+}
+
+void tearDown(void)
+{
+    /* Function run after every test */
+    lv_obj_clean(lv_screen_active());
+}
+
 void test_checkbox_creation_successful(void)
 {
     active_screen = lv_screen_active();
@@ -115,4 +126,13 @@ void test_checkbox_rtl(void)
     TEST_ASSERT_EQUAL_SCREENSHOT("widgets/checkbox_rtl_1.png");
 }
 
+void test_checkbox_style_opa(void)
+{
+    lv_obj_t * obj = lv_checkbox_create(lv_screen_active());
+    lv_obj_set_style_opa(obj, LV_OPA_0, LV_PART_INDICATOR);
+    lv_obj_center(obj);
+
+    TEST_ASSERT_EQUAL_SCREENSHOT("widgets/checkbox_1.png");
+}
+
 #endif