paging: preserve the cursor's viewport-relative row (IDA-style)

PageUp/Down and Ctrl+U/D now move the scroll top and the cursor by the same
(clamped) delta, so the cursor keeps its relative screen row instead of snapping
to an edge; at the very top/bottom the cursor jumps to the extreme. Shared
_page_scroll in ColumnCursor, used by both views. pilot suite 49/49.

2 files changed, 46 insertions, 12 deletions

diff --git a/idatui/app.py b/idatui/app.py
index 497f0ac..87420c2 100644
--- a/idatui/app.py
+++ b/idatui/app.py
@@ -301,6 +301,31 @@ class ColumnCursor:
         if event.chain >= 2:  # double-click == place cursor + follow
             self.post_message(FollowRequested(self))
 
+    # -- paging (keeps the cursor at the same viewport-relative row) ------- #
+    def _page_scroll(self, lines: int) -> None:
+        total = self.total
+        if total <= 0:
+            return
+        height = self._visible_height()
+        top = round(self.scroll_offset.y)
+        max_top = max(total - height, 0)
+        new_top = max(0, min(max_top, top + lines))
+        delta = new_top - top
+        if delta == 0:  # already at an edge: jump the cursor to the extreme
+            self.cursor = (total - 1) if lines > 0 else 0
+        else:  # move cursor by the same delta -> relative row preserved
+            self.cursor = max(0, min(total - 1, self.cursor + delta))
+        self._clamp_x()
+        self.scroll_to(y=new_top, animate=False)
+        self.refresh()
+        self._after_cursor_move()
+
+    def action_page(self, direction: int) -> None:
+        self._page_scroll(direction * self._visible_height())
+
+    def action_half_page(self, direction: int) -> None:
+        self._page_scroll(direction * (self._visible_height() // 2))
+
 
 class SearchMixin:
     """Vim-style in-view search shared by the disasm and pseudocode views.
@@ -698,12 +723,6 @@ class DisasmView(SearchMixin, NavMixin, ColumnCursor, ScrollView, can_focus=True
     def action_cursor_up(self) -> None:
         self._move(-1)
 
-    def action_half_page(self, direction: int) -> None:
-        self._move(direction * (self._visible_height() // 2))
-
-    def action_page(self, direction: int) -> None:
-        self._move(direction * self._visible_height())
-
     def action_goto_top(self) -> None:
         self._move(-self.total)
 
@@ -869,12 +888,6 @@ class DecompView(SearchMixin, NavMixin, ColumnCursor, ScrollView, can_focus=True
     def action_cursor_up(self) -> None:
         self._move(-1)
 
-    def action_half_page(self, direction: int) -> None:
-        self._move(direction * (self._visible_height() // 2))
-
-    def action_page(self, direction: int) -> None:
-        self._move(direction * self._visible_height())
-
     def action_goto_top(self) -> None:
         self._move(-len(self._strips))
 
diff --git a/tests/test_tui.py b/tests/test_tui.py
index 688df57..47c5a67 100644
--- a/tests/test_tui.py
+++ b/tests/test_tui.py
@@ -501,6 +501,27 @@ async def run(db):
               round(dis.scroll_offset.y) == want_sy and dis.cursor == want_cur,
               f"scroll={round(dis.scroll_offset.y)} (want {want_sy}) cursor={dis.cursor}")
 
+        # PageUp/Down keep the cursor at the same viewport-relative row.
+        await goto_name(fa.name)
+        await wait_until(pilot, lambda: dis.total > 100 and app._cur.ea == fa.addr, timeout=20)
+        if app._active != "disasm":
+            await pilot.press("tab")
+        await pilot.pause(0.2)
+        for _ in range(6):
+            await pilot.press("j")
+        await pilot.pause(0.1)
+        rel = dis.cursor - round(dis.scroll_offset.y)
+        await pilot.press("pagedown")
+        await pilot.pause(0.1)
+        check("PageDown preserves the viewport-relative row",
+              dis.cursor - round(dis.scroll_offset.y) == rel,
+              f"rel={dis.cursor - round(dis.scroll_offset.y)} want={rel}")
+        await pilot.press("pageup")
+        await pilot.pause(0.1)
+        check("PageUp preserves the viewport-relative row",
+              dis.cursor - round(dis.scroll_offset.y) == rel,
+              f"rel={dis.cursor - round(dis.scroll_offset.y)} want={rel}")
+
 
 def main(argv):
     db = None