fix(buttonmatrix): skip buttons outside clip area in draw_main

draw_main iterates all buttons unconditionally, performing style
resolution and draw dispatch even for buttons outside the clip area.
Add an lv_area_is_on() check to skip buttons that don't intersect
the layer's clip area.

The test area is extended by the same margin used in
invalidate_button_area (row/col gap with dpi/10 minimum) to account
for outline and shadow rendering outside the base button area. The
popover flag additionally extends the test area upward by the
button's height.

Signed-off-by: Andrew Leech <andrew.leech@planetinnovation.com.au>

Author: pi-anl

src/widgets/buttonmatrix/lv_buttonmatrix.c

@@ -653,6 +653,19 @@ static void draw_main(lv_event_t * e)
     int32_t pleft = lv_obj_get_style_pad_left(obj, LV_PART_MAIN);
     int32_t pright = lv_obj_get_style_pad_right(obj, LV_PART_MAIN);
 
+    /*Clip margin for the early skip check below.  Buttons can render outside
+     *their base area due to outline/shadow, so extend the test area by the
+     *same margin used in invalidate_button_area (row/col gap, dpi/10 min).*/
+    int32_t clip_margin;
+    {
+        int32_t row_gap = lv_obj_get_style_pad_row(obj, LV_PART_MAIN);
+        int32_t col_gap = lv_obj_get_style_pad_column(obj, LV_PART_MAIN);
+        int32_t dpi_margin = lv_display_get_dpi(lv_obj_get_display(obj)) / 10;
+        row_gap = LV_MAX(row_gap, dpi_margin);
+        col_gap = LV_MAX(col_gap, dpi_margin);
+        clip_margin = LV_MAX(row_gap, col_gap);
+    }
+
 #if LV_USE_ARABIC_PERSIAN_CHARS
     char txt_ap[256];
 #endif
@@ -685,6 +698,20 @@ static void draw_main(lv_event_t * e)
         btn_area.x2 += area_obj.x1;
         btn_area.y2 += area_obj.y1;
 
+        /*Skip buttons outside the clip area.  Extend the test area by
+         *clip_margin (shadow/outline) and popover height when applicable.*/
+        {
+            lv_area_t clip_test = btn_area;
+            clip_test.x1 -= clip_margin;
+            clip_test.y1 -= clip_margin;
+            clip_test.x2 += clip_margin;
+            clip_test.y2 += clip_margin;
+            if(btnm->ctrl_bits[btn_i] & LV_BUTTONMATRIX_CTRL_POPOVER) {
+                clip_test.y1 -= lv_area_get_height(&btn_area);
+            }
+            if(!lv_area_is_on(&clip_test, &layer->_clip_area)) continue;
+        }
+
         /*Set up the draw descriptors*/
         if(btn_state == LV_STATE_DEFAULT) {
             lv_memcpy(&draw_rect_dsc_act, &draw_rect_dsc_def, sizeof(lv_draw_rect_dsc_t));