scroll.py

def scroll_forward(w, b, half=False):
    """
    Scroll window down.
    """

    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(w, b, half=False):
    """
    Scroll window up.
    """

    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(w, b):
    """
    Same as ControlF, but only scroll half a page.
    """
    scroll_forward(w, b, half=True)


def scroll_half_page_up(w, b):
    """
    Same as ControlB, but only scroll half a page.
    """
    scroll_backward(w, b, half=True)


def scroll_one_line_down(w, b):
    """
    scroll_offset += 1
    """

    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(w, b):
    """
    scroll_offset -= 1
    """

    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(w, b):
    """
    Scroll page down. (Prefer the cursor at the top of the page, after scrolling.)
    """

    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(w, b):
    """
    Scroll page up. (Prefer the cursor at the bottom of the page, after scrolling.)
    """

    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