<html> <head> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"> <style type="text/css" style="display:none;"></style> </head> <body dir="ltr"> <div id="divtagdefaultwrapper" style="font-size:12pt;color:#000000;font-family:Calibri,Helvetica,sans-serif;" dir="ltr"> <div style=""> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">Hi there,</p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;"> </p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">Is there any definitive word about whether or not clients should be expected or allowed to <span style="">premultiply</span> alpha the alpha channels in the normal EGL and linux-dmabuf buffers they send to a compositor?</p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;"><br> </p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">I have never seen this practice used with Wayland -- t<span style="font-family: Calibri, sans-serif; font-size: 14.6667px;">he shaders in the gl-renderer certainly don't seem to expect clients to premultiply. B</span>ut I stumbled on a comment or two that maybe gnome-calculator [1] does this and that Sway settled on that convention [2].</p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;"> </p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">I see hardly any mention of <span style="">premult</span> in the Weston codebase. In fact, the only real reference to it occurs at a site dealing with <span style="">Pixman</span> color formats. In this location, it's a prominent warning to the reader that <span style="">Pixman</span> does use <span style="">premultiplication</span>; this seems to carry the meaning that Pixman's premult usage stands apart from the rest of Weston.</p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;"><br> </p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">To me, it seems that Wayland's adoption of the DRM_FORMAT_xxx identifiers in the wire protocols (e.g., dmabuf) combined with drm_fourcc.h's complete stonewalled silence on the subject, seems to be a fairly strong indicating that premultiplication should not be used.</p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;"> </p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">-Matt</p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;"><br> </p> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">[1] <a href="https://github.com/swaywm/wlroots/issues/984#issue-324334642" class="OWAAutoLink" id="LPlnk92704" previewremoved="true">https://github.com/swaywm/wlroots/issues/984#issue-324334642</a></p> <br> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;">[2] <a href="https://github.com/swaywm/wlroots/issues/984#issuecomment-390221778" class="OWAAutoLink" id="LPlnk687581" previewremoved="true">https://github.com/swaywm/wlroots/issues/984#issuecomment-390221778</a></p> <br> <div> <div> <p style="margin: 0in; font-size: 11pt; font-family: Calibri, sans-serif;"> </p> </div> </div> </div> </div> </body> </html>