r269471 make unusable VT console

Nathan Whitehorn nwhitehorn at freebsd.org
Tue Aug 19 17:47:04 UTC 2014

On 08/19/14 09:28, Jean-Sébastien Pédron wrote:
> On 19.08.2014 10:42, Jean-Sébastien Pédron wrote:
>> On 16.08.2014 01:51, Nathan Whitehorn wrote:
>>> It also has bad effects on boot time. My desktop takes something like 3
>>> times as long to boot after r269471. If it can't be fixed quickly, it
>>> needs to be reverted.
>> Just a quick note: I'm working on an update to vt_vga.
> Hello!
> Here's a first version of the patch I was talking about:
> https://people.freebsd.org/~dumbbell/vt/vt-vga.5.patch


> What's new/fixed:
>      o  vt_vga introduces a new callback, vd_bitblt_text_t, which takes
>         as argument the text buffer, the dirty area, the font and the
>         cursor (position, map, colors). With all this information at
>         hand, it can redraw the dirty area with almost no read from the
>         video memory. This greatly improves the performance. The
>         implementation is quite naive and I put a lot of comments. This
>         could probably be simplfied/improved.
>         The cursor is drawn at the same time than the text: this avoids
>         flickering of the mouse pointer.
>         The patch reads from the video memory only when the byte to
>         write uses more than 2 colors (fg/bg). But this only happens
>         with colored text around the cursor or with fonts who's width
>         isn't a multiple of 8.

Why is this necessary? I'd really prefer to avoid complicating this API. 
One of the great things about writing newcons drivers is that there is 
basically only one function you need to implement. If the current API 
does not provide enough information to do this efficiently, I'd much 
rather change it than add new callbacks.

>      o  In vt_flush(), handle the cursor position before getting the
>         dirty area. This fixes a bug where, if we move the cursor too
>         fast, its new location is outside the marked area and it
>         disappears from the screen.
>         While here, mark the new position of the cursor as dirty, not
>         only the old one.
>         For the cursor to be drawn, VWF_MOUSE_HIDE must not be set *and*
>         VDF_MOUSECURSOR must be set! Before, only the former was checked
>         when deciding if the cursor position should be marked as dirty.
>         Finally, if the cursor didn't move, don't mark its position as
>         dirty.
>         Before, these two problems caused major redraw of a large part
>         of the screen for nothing, due to a mouse pointer location of
>        [0;0] (even if disabled) and its position always marked as dirty.
>      o  When the mouse state is changed, mark its position as dirty.
>      o  The flush timer is paused during a window switch. In the case of
>         vt_vga, vga_initialize() is called and it messes with VGA
>         registers and the video memory. If vt_flush() is triggered at
>         the same time, unexpected data are displayed. This is fixed,
>         though, there's still a annoying flickering, because the sync
>         signal is temporarily stopped during vga_initialize().
>      o  The patch includes another non-related patch, which tries to
>         stabilize the refresh rate. Currently, we schedule the next
>         redraw in 40 ms (25 Hz), but that doesn't count for the time
>         taken to redraw.
>      o  Change how the mouse is enabled/disabled/shown/hidden. Now, the
>         GETLEVEL and GETMODE ioctls don't touch this. Everything goes
>         through the CONS_MOUSECTL ioctl. This fixes vidcontrol -m on|off.
> Known issues:
>      o  Instead of having an "if (bitblt_text != NULL)" check in
>         vt_flush(), I'll add a generic bitblt_text callback which
>         implements the old code, so that other drivers can be changed
>         incrementally.
>      o  In vt_vga, the screen flickers during a window switch, because
>         it stops the sync signal and zeroes the memory. It would be nice
>         to avoid that.
>      o  Several issues when the font is changed:
>           1. The offset to center the text area is global, not per
>              window. Therefore other window are not centered anymore.
>           2. There's a bug with my patch, where other windows have the
>              top-left letter wrongly shifted.
>           3. When the text area changes (compared to the whole screen),
>              there's garbage in the borders.
>           4. The text cursor (the square) may be broken on other windows.
>      o  The mouse pointer is somtimes not erased during a move.
>      o  The text square cursor handling in vt_vga could be improved:
>         colors are just reversed, we shouldn't change the fg/bg colors,
>         just write a 0x00 pattern instead.
>      o  The vt_flush() timer could maybe be stopped when there's nothing
>         to draw. No need to wakeup a core for that.
> Any comments?

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