fix(core): fix scrollbar position overflows for huge content sizes (#9871)

src/core/lv_obj_scroll.c

@@ -35,6 +35,7 @@
 /**********************
  *  STATIC PROTOTYPES
  **********************/
+static inline int32_t mul_div(int32_t v, int32_t factor, int32_t divisor);
 static void scroll_x_anim(void * obj, int32_t v);
 static void scroll_y_anim(void * obj, int32_t v);
 static void scroll_end_cb(lv_anim_t * a);
@@ -600,7 +601,7 @@ void lv_obj_get_scrollbar_area(lv_obj_t * obj, lv_area_t * hor_area, lv_area_t *
             ver_area->x1 = ver_area->x2 - thickness + 1;
         }
 
-        int32_t sb_h = ((obj_h - top_space - bottom_space - hor_req_space) * obj_h) / content_h;
+        int32_t sb_h = mul_div(obj_h - top_space - bottom_space - hor_req_space, obj_h, content_h);
         sb_h = LV_MAX(length > 0 ? length : sb_h, SCROLLBAR_MIN_SIZE); /*Style-defined size, calculated size, or minimum size*/
         sb_h = LV_MIN(sb_h, obj_h); /*Limit scrollbar length to parent height*/
         rem = (obj_h - top_space - bottom_space - hor_req_space) -
@@ -611,7 +612,7 @@ void lv_obj_get_scrollbar_area(lv_obj_t * obj, lv_area_t * hor_area, lv_area_t *
             ver_area->y2 = obj->coords.y2 - bottom_space - hor_req_space - 1;
         }
         else {
-            int32_t sb_y = (rem * sb) / scroll_h;
+            int32_t sb_y = mul_div(rem, sb, scroll_h);
             sb_y = rem - sb_y;
 
             ver_area->y1 = obj->coords.y1 + sb_y + top_space;
@@ -639,7 +640,7 @@ void lv_obj_get_scrollbar_area(lv_obj_t * obj, lv_area_t * hor_area, lv_area_t *
         hor_area->x1 = obj->coords.x1;
         hor_area->x2 = obj->coords.x2;
 
-        int32_t sb_w = ((obj_w - left_space - right_space - ver_reg_space) * obj_w) / content_w;
+        int32_t sb_w = mul_div(obj_w - left_space - right_space - ver_reg_space, obj_w, content_w);
         sb_w = LV_MAX(length > 0 ? length : sb_w, SCROLLBAR_MIN_SIZE); /*Style-defined size, calculated size, or minimum size*/
         sb_w = LV_MIN(sb_w, obj_w); /*Limit scrollbar length to parent width*/
         rem = (obj_w - left_space - right_space - ver_reg_space) -
@@ -656,7 +657,7 @@ void lv_obj_get_scrollbar_area(lv_obj_t * obj, lv_area_t * hor_area, lv_area_t *
             }
         }
         else {
-            int32_t sb_x = (rem * sr) / scroll_w;
+            int32_t sb_x = mul_div(rem, sr, scroll_w);
             sb_x = rem - sb_x;
 
             if(rtl) {
@@ -748,6 +749,11 @@ void lv_obj_readjust_scroll(lv_obj_t * obj, lv_anim_enable_t anim_en)
  *   STATIC FUNCTIONS
  **********************/
 
+static inline int32_t mul_div(int32_t v, int32_t factor, int32_t divisor)
+{
+    return ((int64_t)v * factor) / divisor;
+}
+
 static void scroll_x_anim(void * obj, int32_t v)
 {
     lv_obj_scroll_by_raw(obj, v + lv_obj_get_scroll_x(obj), 0);

tests/src/test_cases/test_scrollbar.c

@@ -0,0 +1,52 @@
+#if LV_BUILD_TEST
+#include "../lvgl.h"
+#include "../../lvgl_private.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_scrollbar_vertical(void)
+{
+    lv_obj_set_flex_flow(lv_screen_active(), LV_FLEX_FLOW_ROW);
+
+    const int32_t inner_sizes[] = {100, 500, 1000, 5000, 100000, 500000, 1000000, 4000000};
+    for(size_t i = 0; i < sizeof(inner_sizes) / sizeof(inner_sizes[0]); i++) {
+        lv_obj_t * wrapper = lv_obj_create(lv_screen_active());
+        lv_obj_set_flex_grow(wrapper, 1);
+        lv_obj_set_height(wrapper, LV_PCT(100));
+
+        lv_obj_t * inner = lv_obj_create(wrapper);
+        lv_obj_set_size(inner, LV_PCT(100), inner_sizes[i]);
+    }
+
+    TEST_ASSERT_EQUAL_SCREENSHOT("scrollbar_vertical.png");
+}
+
+void test_scrollbar_horizontal(void)
+{
+    lv_obj_set_flex_flow(lv_screen_active(), LV_FLEX_FLOW_COLUMN);
+
+    const int32_t inner_sizes[] = {100, 500, 1000, 5000, 100000, 500000, 1000000, 4000000};
+    for(size_t i = 0; i < sizeof(inner_sizes) / sizeof(inner_sizes[0]); i++) {
+        lv_obj_t * wrapper = lv_obj_create(lv_screen_active());
+        lv_obj_set_flex_grow(wrapper, 1);
+        lv_obj_set_width(wrapper, LV_PCT(100));
+
+        lv_obj_t * inner = lv_obj_create(wrapper);
+        lv_obj_set_size(inner, inner_sizes[i], LV_PCT(100));
+    }
+
+    TEST_ASSERT_EQUAL_SCREENSHOT("scrollbar_horizontal.png");
+}
+
+#endif