clearWrittenWindowsApi

fn clearWrittenWindowsApi(io: Io) WindowsApiError!void

File

Code

fn clearWrittenWindowsApi(io: Io) WindowsApiError!void {
    // This uses a 'marker' strategy. The idea is:
    // - Always write a marker (in this case U+25BA or ►) at the beginning of the progress
    // - Get the current cursor position (at the end of the progress)
    // - Subtract the number of lines written to get the expected start of the progress
    // - Check to see if the first character at the start of the progress is the marker
    // - If it's not the marker, keep checking the line before until we find it
    // - Clear the screen from that position down, and set the cursor position to the start
    //
    // This strategy works even if there is line wrapping, and can handle the window
    // being resized/scrolled arbitrarily.
    //
    // Notes:
    // - Ideally, the marker would be a zero-width character, but the Windows console
    //   doesn't seem to support rendering zero-width characters (they show up as a space)
    // - This same marker idea could technically be done with an attribute instead
    //   (https://learn.microsoft.com/en-us/windows/console/console-screen-buffers#character-attributes)
    //   but it must be a valid attribute and it actually needs to apply to the first
    //   character in order to be readable via ReadConsoleOutputAttribute. It doesn't seem
    //   like any of the available attributes are invisible/benign.
    if (!global_progress.need_clear) return;
    const terminal = global_progress.terminal;
    const screen_area = @as(windows.DWORD, global_progress.cols) * global_progress.rows;

    var get_console_info = windows.CONSOLE.USER_IO.GET_SCREEN_BUFFER_INFO;
    switch (try get_console_info.operate(io, terminal)) {
        .SUCCESS => {},
        else => |status| return windows.unexpectedStatus(status),
    }
    var fill_spaces = windows.CONSOLE.USER_IO.FILL(
        .{ .WideCharacter = ' ' },
        screen_area,
        get_console_info.Data.dwCursorPosition,
    );
    switch (try fill_spaces.operate(io, terminal)) {
        .SUCCESS => {},
        else => |status| return windows.unexpectedStatus(status),
    }
}