<html><head></head><body><div dir="auto">Thank you very much for the breakdown, I totally missed that cairo feature.<br><br>Am I right into thinking that the logical pixels don't need any calculation (apart from when comparing them to pixel information from X, like you said)? So that I just need to change the click handling and surface creation code<br><br>Also, should the size of the surface be (digital * ratio)? So the whole things looks like<br><br>1) get ratio from the monitor<br>2) create surface with size (digital * ratio)<br>3) set cairo device scale to (ratio)<br>4) write normally with digital<br>5) handle x11 events as (device / ratio)<br><br>Did I understood everything correctly?<br><br>Regards<br></div><br><br><div class="gmail_quote"><div dir="auto">On March 20, 2024 1:03:06 PM GMT+01:00, Emmanuele Bassi <ebassi@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>The way "high DPI" support is implemented is typically this:</div><div><br></div><div>- You retrieve the scaling factor from the windowing system; in the case of X11 you can deduce the scaling factor from the ratio between the width and the height of the target monitor: anything below 192 is generally considered "1" and anything above is generally considered "2". If you want to go into fractional scaling territory, you'll likely need some other mechanism, like a user configuration setting.<br></div><div>- Once you have a scaling factor, you create a windowing system surface that has two units:</div><div> 1. device pixels, which are the physical pixels on the monitor</div><div> 2. logical pixels, which are the scaled pixels for drawing operations</div><div><br></div><div>Your surfaces have to be created with the size in device pixels; then you call cairo_surface_set_device_scale() with the scaling factor you computed:</div><div><br></div><div><a href="https://www.cairographics.org/manual/cairo-cairo-surface-t.html#cairo-surface-set-device-scale">https://www.cairographics.org/manual/cairo-cairo-surface-t.html#cairo-surface-set-device-scale</a></div><div><br></div><div>After that, every drawing operation must be in **logical** pixels, and the Cairo will automatically scale every coordinate and size appropriately.</div><div><br></div><div>It is your responsibility to deal with device and logical coordinates; for instance, windowing system events will be in device coordinates, but if you're exposing their information to other code you will need to scale them appropriately.<br></div><div><br></div><div>Ciao,</div><div> Emmanuele.<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, 20 Mar 2024 at 11:47, 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">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 <<a href="mailto:dov.grobgeld@gmail.com" target="_blank">dov.grobgeld@gmail.com</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">
<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" target="_blank">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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