add test

src/core/lv_refr.c

@@ -925,10 +925,22 @@ void refr_obj(lv_layer_t * layer, lv_obj_t * obj)
                                                           area_need_alpha ? LV_COLOR_FORMAT_ARGB8888 : LV_COLOR_FORMAT_NATIVE, &layer_area_act);
             lv_obj_redraw(new_layer, obj);
 
+            lv_point_t pivot = {
+                .x = lv_obj_get_style_transform_pivot_x(obj, 0),
+                .y = lv_obj_get_style_transform_pivot_y(obj, 0)
+            };
+
+            if(LV_COORD_IS_PCT(pivot.x)) {
+                pivot.x = (LV_COORD_GET_PCT(pivot.x) * lv_area_get_width(&obj->coords)) / 100;
+            }
+            if(LV_COORD_IS_PCT(pivot.y)) {
+                pivot.y = (LV_COORD_GET_PCT(pivot.y) * lv_area_get_height(&obj->coords)) / 100;
+            }
+
             lv_draw_image_dsc_t layer_draw_dsc;
             lv_draw_image_dsc_init(&layer_draw_dsc);
-            layer_draw_dsc.pivot.x = obj->coords.x1 + lv_obj_get_style_transform_pivot_x(obj, 0) - new_layer->buf_area.x1;
-            layer_draw_dsc.pivot.y = obj->coords.y1 + lv_obj_get_style_transform_pivot_y(obj, 0) - new_layer->buf_area.y1;
+            layer_draw_dsc.pivot.x = obj->coords.x1 + pivot.x - new_layer->buf_area.x1;
+            layer_draw_dsc.pivot.y = obj->coords.y1 + pivot.y - new_layer->buf_area.y1;
 
             layer_draw_dsc.opa = opa;
             layer_draw_dsc.rotation = lv_obj_get_style_transform_rotation(obj, 0);

tests/src/test_cases/draw/test_layer_transform.c

@@ -0,0 +1,44 @@
+#if LV_BUILD_TEST
+#include "../lvgl.h"
+
+#include "unity/unity.h"
+
+void setUp(void)
+{
+    /* Function run before every test */
+}
+
+void tearDown(void)
+{
+    /* Function run after every test */
+    lv_obj_clean(lv_screen_active());
+}
+
+void test_no_residual_border_on_scale_down(void)
+{
+    lv_obj_t * obj = lv_obj_create(lv_screen_active());
+    lv_obj_set_size(obj, 100, 100);
+    lv_obj_center(obj);
+    lv_obj_set_style_border_color(obj, lv_color_hex3(0xf00), 0);
+    lv_obj_set_style_bg_color(obj, lv_color_hex3(0x0f0), 0);
+    TEST_ASSERT_EQUAL_SCREENSHOT("draw/layer_transform_1.png");
+
+    int32_t pivot_x[] = {lv_pct(50), lv_pct(8),  lv_pct(0), lv_pct(106), lv_pct(-16)};
+    int32_t pivot_y[] = {lv_pct(50), lv_pct(12), lv_pct(0), lv_pct(113), lv_pct(-27)};
+    int32_t scale[] = {256 * 4,      412,        569,       288,         711};
+
+    uint32_t i;
+    for(i = 0; i < 5; i++) {
+        lv_obj_set_style_transform_pivot_x(obj, pivot_x[i], 0);
+        lv_obj_set_style_transform_pivot_y(obj, pivot_y[i], 0);
+        lv_obj_set_style_transform_scale(obj, scale[i], 0);
+        lv_refr_now(NULL);
+
+        /*Should be the same as the original without any artifacts*/
+        lv_obj_set_style_transform_scale(obj, 256, 0);
+        TEST_ASSERT_EQUAL_SCREENSHOT("draw/layer_transform_1.png");
+    }
+
+}
+
+#endif