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List: cairo
Subject: Re: Implementing HiDpi scaling
From: Federico Angelilli <list () fedang ! net>
Date: 2024-03-20 11:36:34
Message-ID: 5FD945CD-5641-4A63-963F-3140F6513831 () fedang ! net
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Hello,
Sorry for the late reply.
I am using cairo for drawing and pango for the text. I am creating a window with xcb \
and using cairo_xcb_surface.
I can easily extract the dpi information from the xrandr api calls. Now that I have \
this ratio, I have to use it somewhere to scale my canvas appropriately.
I will try using cairo_scale, and should I also scale the size of the xcb_surface by \
the same ratio?
Anyway my main concern about antialising is that since I am making layered shapes \
(think buttons) the border and the background will not match up pixel perfect (which \
is something that I have seen in other project using cairo).
Does what I described about scaling the surface makes sense or am I misinterpreting \
cairo_scale?
Regards
Ps:
I will soon try and post the results
On March 18, 2024 1:46:54 PM GMT+01:00, Dov Grobgeld <dov.grobgeld@gmail.com> wrote:
> I think that you should describe in detail what you expect.
>
> In pure vector graphics a contour may cut through a pixel and partially
> obscure it, and it is then the responsibility of the graphics engine to
> create anti-aliased graphics by mixing the colors of the background and the
> foreground. As a user you typically don't need to concern yourself with
> that as it is done automatically.
>
> However, e.g. for text this may cause "fuzzy" characters and the engine
> will then fallback to moving the contours and scale the font so that the
> glyphs fall on whole pixels.
>
> Note that the use of anti-aliased graphics is less needed, and less
> visible, for an HDPI device.
>
> In any case all that you will typically need is cairo_scale() as Uli
> Shlachter already described.
>
> Try it!
>
> Regards,
>
>
> On Sun, Mar 17, 2024 at 12:46 PM Federico Angelilli <list@fedang.net> wrote:
>
> > Hi
> >
> > Will cairo_scale make a pixel perfect image for non integer scales? To my
> > understanding the scale matrix will be multiplied to all the coordinates
> > scaling the coordinates appropriately. Should I also scale the whole
> > surface by that same factor?
> >
> > Regards
> >
> >
> > On March 16, 2024 6:27:56 PM GMT+01:00, Uli Schlachter <psychon@znc.in>
> > wrote:
> >
> > > Hi
> > >
> > > Am 14.03.24 um 16:34 schrieb fedang:
> > >
> > > > Hello all,
> > > >
> > > > I am writing a small X11 app using cairo as the drawing backend. I was \
> > > > wondering if and how to implement fractional scaling to accommodate high dpi \
> > > > screens. After searching online I found almost nothing, so here I am.
> > > > Can someone give me some pointers on what to do? I can get a scale factor for \
> > > > the screens (depending on the size) but I have no idea how to actually use it \
> > > > in the draw code.
> > >
> > > I'm not sure if I understand the question. You can use cairo_scale() to set a \
> > > scale factor for all drawing. So I would say that you can just apply the scale \
> > > factor with cairo_scale() before drawing.
> > > Of course, this assumes that you don't use cairo_identity_matrix() or \
> > > cairo_set_matrix() in your drawing. Instead, cairo_save() and cairo_restore() \
> > > should be used around temporary modifications of the transformations.
> > > Cheers,
> > > Uli
> > >
> > >
[Attachment #3 (text/html)]
<html><head></head><body><div dir="auto">Hello,<br>Sorry for the late reply.<br><br>I \
am using cairo for drawing and pango for the text. I am creating a window with xcb \
and using cairo_xcb_surface.<br><br>I can easily extract the dpi information from the \
xrandr api calls. Now that I have this ratio, I have to use it somewhere to scale my \
canvas appropriately.<br><br>I will try using cairo_scale, and should I also scale \
the size of the xcb_surface by the same ratio?<br><br>Anyway my main concern about \
antialising is that since I am making layered shapes (think buttons) the border and \
the background will not match up pixel perfect (which is something that I have seen \
in other project using cairo).<br><br>Does what I described about scaling the surface \
makes sense or am I misinterpreting cairo_scale?<br><br>Regards<br><br>Ps:<br>I will \
soon try and post the results <br></div><br><br><div class="gmail_quote"><div \
dir="auto">On March 18, 2024 1:46:54 PM GMT+01:00, Dov Grobgeld \
<dov.grobgeld@gmail.com> wrote:</div><blockquote class="gmail_quote" \
style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); \
padding-left: 1ex;"> <div dir="ltr"><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif">I think that you should describe in \
detail what you expect.</div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif">In pure vector graphics a contour may \
cut through a pixel and partially obscure it, and it is then the responsibility of \
the graphics engine to create anti-aliased graphics by mixing the colors of the \
background and the foreground. As a user you typically don't need to concern yourself \
with that as it is done automatically.</div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif">However, e.g. for text this may cause \
"fuzzy" characters and the engine will then fallback to moving the contours and scale \
the font so that the glyphs fall on whole pixels.</div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif">Note that the use of anti-aliased \
graphics is less needed, and less visible, for an HDPI device.</div><div \
class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div \
class="gmail_default" style="font-family:arial,helvetica,sans-serif">In any case all \
that you will typically need is cairo_scale() as Uli Shlachter already described. \
<br></div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif"><br></div><div class="gmail_default" \
style="font-family:arial,helvetica,sans-serif">Try it!</div><div \
class="gmail_default" style="font-family:arial,helvetica,sans-serif"><br></div><div \
class="gmail_default" \
style="font-family:arial,helvetica,sans-serif">Regards,</div><div \
class="gmail_default" \
style="font-family:arial,helvetica,sans-serif"><br></div></div><br><div \
class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Mar 17, 2024 at \
12:46 PM Federico Angelilli <<a \
href="mailto:list@fedang.net">list@fedang.net</a>> wrote:<br></div><blockquote \
class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid \
rgb(204,204,204);padding-left:1ex"><div><div dir="auto">Hi<br><br>Will cairo_scale \
make a pixel perfect image for non integer scales? To my understanding the scale \
matrix will be multiplied to all the coordinates scaling the coordinates \
appropriately. Should I also scale the whole surface by that same \
factor?<br><br>Regards</div><br><br><div class="gmail_quote"><div dir="auto">On March \
16, 2024 6:27:56 PM GMT+01:00, Uli Schlachter <<a href="mailto:psychon@znc.in" \
target="_blank">psychon@znc.in</a>> wrote:</div><blockquote class="gmail_quote" \
style="margin:0pt 0pt 0pt 0.8ex;border-left:1px solid \
rgb(204,204,204);padding-left:1ex"> <pre><div dir="auto">Hi<br><br>Am 14.03.24 um \
16:34 schrieb fedang:<br></div><blockquote class="gmail_quote" style="margin:0pt 0pt \
1ex 0.8ex;border-left:1px solid rgb(114,159,207);padding-left:1ex"><div \
dir="auto">Hello all,<br><br>I am writing a small X11 app using cairo as the drawing \
backend. I was wondering if and how to implement<br>fractional scaling to accommodate \
high dpi screens. After searching online I found almost nothing, so here I \
am.<br><br>Can someone give me some pointers on what to do? I can get a scale factor \
for the screens (depending on the size)<br>but I have no idea how to actually use it \
in the draw code.<br></div></blockquote><div dir="auto"><br>I'm not sure if I \
understand the question. You can use cairo_scale() to set a scale factor for all \
drawing. So I would say that you can just apply the scale factor with cairo_scale() \
before drawing.<br><br>Of course, this assumes that you don't use \
cairo_identity_matrix() or cairo_set_matrix() in your drawing. Instead, cairo_save() \
and cairo_restore() should be used around temporary modifications of the \
transformations.<br><br>Cheers,<br>Uli<br></div></pre></blockquote></div></div></blockquote></div>
</blockquote></div></body></html>
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