1 files changed, 189 insertions, 0 deletions
diff --git a/src/prompt_toolkit/key_binding/bindings/scroll.py b/src/prompt_toolkit/key_binding/bindings/scroll.py
new file mode 100644
index 0000000..83a4be1
--- /dev/null
+++ b/src/prompt_toolkit/key_binding/bindings/scroll.py
@@ -0,0 +1,189 @@
+"""
+Key bindings, for scrolling up and down through pages.
+
+This are separate bindings, because GNU readline doesn't have them, but
+they are very useful for navigating through long multiline buffers, like in
+Vi, Emacs, etc...
+"""
+from __future__ import annotations
+
+from prompt_toolkit.key_binding.key_processor import KeyPressEvent
+
+__all__ = [
+    "scroll_forward",
+    "scroll_backward",
+    "scroll_half_page_up",
+    "scroll_half_page_down",
+    "scroll_one_line_up",
+    "scroll_one_line_down",
+]
+
+E = KeyPressEvent
+
+
+def scroll_forward(event: E, half: bool = False) -> None:
+    """
+    Scroll window down.
+    """
+    w = event.app.layout.current_window
+    b = event.app.current_buffer
+
+    if w and w.render_info:
+        info = w.render_info
+        ui_content = info.ui_content
+
+        # Height to scroll.
+        scroll_height = info.window_height
+        if half:
+            scroll_height //= 2
+
+        # Calculate how many lines is equivalent to that vertical space.
+        y = b.document.cursor_position_row + 1
+        height = 0
+        while y < ui_content.line_count:
+            line_height = info.get_height_for_line(y)
+
+            if height + line_height < scroll_height:
+                height += line_height
+                y += 1
+            else:
+                break
+
+        b.cursor_position = b.document.translate_row_col_to_index(y, 0)
+
+
+def scroll_backward(event: E, half: bool = False) -> None:
+    """
+    Scroll window up.
+    """
+    w = event.app.layout.current_window
+    b = event.app.current_buffer
+
+    if w and w.render_info:
+        info = w.render_info
+
+        # Height to scroll.
+        scroll_height = info.window_height
+        if half:
+            scroll_height //= 2
+
+        # Calculate how many lines is equivalent to that vertical space.
+        y = max(0, b.document.cursor_position_row - 1)
+        height = 0
+        while y > 0:
+            line_height = info.get_height_for_line(y)
+
+            if height + line_height < scroll_height:
+                height += line_height
+                y -= 1
+            else:
+                break
+
+        b.cursor_position = b.document.translate_row_col_to_index(y, 0)
+
+
+def scroll_half_page_down(event: E) -> None:
+    """
+    Same as ControlF, but only scroll half a page.
+    """
+    scroll_forward(event, half=True)
+
+
+def scroll_half_page_up(event: E) -> None:
+    """
+    Same as ControlB, but only scroll half a page.
+    """
+    scroll_backward(event, half=True)
+
+
+def scroll_one_line_down(event: E) -> None:
+    """
+    scroll_offset += 1
+    """
+    w = event.app.layout.current_window
+    b = event.app.current_buffer
+
+    if w:
+        # When the cursor is at the top, move to the next line. (Otherwise, only scroll.)
+        if w.render_info:
+            info = w.render_info
+
+            if w.vertical_scroll < info.content_height - info.window_height:
+                if info.cursor_position.y <= info.configured_scroll_offsets.top:
+                    b.cursor_position += b.document.get_cursor_down_position()
+
+                w.vertical_scroll += 1
+
+
+def scroll_one_line_up(event: E) -> None:
+    """
+    scroll_offset -= 1
+    """
+    w = event.app.layout.current_window
+    b = event.app.current_buffer
+
+    if w:
+        # When the cursor is at the bottom, move to the previous line. (Otherwise, only scroll.)
+        if w.render_info:
+            info = w.render_info
+
+            if w.vertical_scroll > 0:
+                first_line_height = info.get_height_for_line(info.first_visible_line())
+
+                cursor_up = info.cursor_position.y - (
+                    info.window_height
+                    - 1
+                    - first_line_height
+                    - info.configured_scroll_offsets.bottom
+                )
+
+                # Move cursor up, as many steps as the height of the first line.
+                # TODO: not entirely correct yet, in case of line wrapping and many long lines.
+                for _ in range(max(0, cursor_up)):
+                    b.cursor_position += b.document.get_cursor_up_position()
+
+                # Scroll window
+                w.vertical_scroll -= 1
+
+
+def scroll_page_down(event: E) -> None:
+    """
+    Scroll page down. (Prefer the cursor at the top of the page, after scrolling.)
+    """
+    w = event.app.layout.current_window
+    b = event.app.current_buffer
+
+    if w and w.render_info:
+        # Scroll down one page.
+        line_index = max(w.render_info.last_visible_line(), w.vertical_scroll + 1)
+        w.vertical_scroll = line_index
+
+        b.cursor_position = b.document.translate_row_col_to_index(line_index, 0)
+        b.cursor_position += b.document.get_start_of_line_position(
+            after_whitespace=True
+        )
+
+
+def scroll_page_up(event: E) -> None:
+    """
+    Scroll page up. (Prefer the cursor at the bottom of the page, after scrolling.)
+    """
+    w = event.app.layout.current_window
+    b = event.app.current_buffer
+
+    if w and w.render_info:
+        # Put cursor at the first visible line. (But make sure that the cursor
+        # moves at least one line up.)
+        line_index = max(
+            0,
+            min(w.render_info.first_visible_line(), b.document.cursor_position_row - 1),
+        )
+
+        b.cursor_position = b.document.translate_row_col_to_index(line_index, 0)
+        b.cursor_position += b.document.get_start_of_line_position(
+            after_whitespace=True
+        )
+
+        # Set the scroll offset. We can safely set it to zero; the Window will
+        # make sure that it scrolls at least until the cursor becomes visible.
+        w.vertical_scroll = 0