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List: cairo
Subject: Re: Implementing HiDpi scaling
From: Dov Grobgeld <dov.grobgeld () gmail ! com>
Date: 2024-03-18 12:46:54
Message-ID: CA++fsGEYoyUi9smjOx5_r4m2PYtwerqCiDa-AqaiPbVJ+==V+Q () mail ! gmail ! com
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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)]
<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>
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