bitmaps or no?
ilan at tzirechnoy.com
Fri Dec 4 11:58:28 UTC 2020
On Tue, Dec 01, 2020 at 07:36:20PM -0500, James K. Lowden wrote:
> I have a basic how-does-one question about scrolling text in a window.
> I have the beginnings of an application that reads troff ditroff output
> and renders it on-screen. The underlying libraries are
> -lGL -lglut -lX11 -lXi -lXft -lfontconfig -lcairo -lfreetype
> Let's say the rendering has room for improvement, and is already better
> than xman(1).
> My question is: how to scroll pages of text?
> The troff output is potentially many pages, and the user will want to
> scroll up and down, as he does, say, viewing the bash(1) manual in GNU
> Currently I open a cairo surface on the main window. Scrolling a
> screen of text up one line would require ... something. I could erase
> the whole thing and start over with line 2 at the top, replacing line
> An alternative, I think, is to render the whole document to a bitmap,
> and scroll the bitmap up and down using just X primitives. That
I suggest to use some pixmap (or perhaps pixmap-backed cairo
surface) reasonably larger than a window, but not a whole docu-
ment. Simple scrolling would be rather fast (all the data is al-
ready rendered, you should just copy it somehow inside one
pixmap), and you could draw the new areas off-screen somewhat
On the other side, a whole troff document with hundreds A4 pages
with a reasonable 200 dpi resolution and 8-bit grayscale an-
tialiasing render -- may take more that a gig of RAM, causing un-
More information about the xorg