Re: Display issues (Was: Next GNUstep release)

[Fred Kiefer]

> Am 28.02.2020 um 11:37 schrieb Riccardo Mottola <address@hidden>:
> Sergii Stoian wrote:
>> 
>>> On Feb 27, 2020, at 23:09, Riccardo Mottola <address@hidden> wrote:
>>> 
>>> before a release, I would like these issues to find a solution.
>>> 
>>> - understand why we don't work properly on my ThinkPad T23 neither with the 
>>> Cairo nor with the xlib backend with similar issues
>> Could you please be more specific and describe these issues?
> 
> I have an issue I am working on with Fred, I can forward you some mail 
> because they contain screenshot and I did not spam the mailing list.
> 
> Essentially I discovered that many windows contain "garbage" and what we 
> discovered so far
> - certain windows width cause garbage do be displayed, resizing the window 
> may cause it do display correctly
> - this garbage is compatible with an wrong offset increasing for each row 
> (you see diagonal lines if  you have a white window with a border)
> - the issue happens both with cairo and xlib (recent discovery of two days 
> ago, before we were concentrating on a cairo issue)
> 
> it looks like an issue that somwehre a padding/alignment is lost: e.g. 
> width*bytesPerPixel != bytesPerRow, but where?
> 
> I have not seen this issue elsewhere. The T23 is itself a pretty standard 
> setup: Devuan ascii, GCC runtime, i386. Only the videocard is a little bit 
> vintage/odd (S3) but it works with any other program except GNUstep :-P

You forgot to mention one important detail. This problem only shows up with 16 
bit depth. Most likely this happens as some data structure that holds the 
intermediate pixel information rounds the line length to a multiple of 8, 16, 
32 or even 64 and we use one value below that, so we get an offset for each 
line which leads to the displayed garbage. The problem is that I am not able to 
reproduce the issue and don’t know which intermediate structure needs 
adjustment.