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<p class="MsoNormal"><span lang="EN-CA">During the AHG meeting there was mention of the idea of supporting additional compositing modes than ‘glyf’ currently supports by using a COLR table. The suggestion was that, if there is a COLR table but no CPAL table,
then that would be an indication for a rasterizer that it should use the COLR table to get composite glyph descriptions.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">It was mentioned that, without a CPAL, there couldn’t be an colour references (COLR doesn’t have any default colours). That means that various Paint table formats can’t be used: Paint(Var)Solid, Paint(Var)LinearGradient,
Paint(Var)RadialGradient, and Paint(Var)SweepGradient. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">But that leaves several other formats to be supported. It’s worth calling out that there’s a fair amount more functionality — hence complexity — than ‘glyf’ composites:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<ul style="margin-top:0in" type="disc">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span lang="EN-CA">PaintComposite has several compositing modes — the benefit that is the motivation behind this proposal. But note that it also supports several colour blending modes
that involve more than Boolean operations on pixel values.<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span lang="EN-CA">Twenty transform formats (granted, most of these are storage optimizations of a matrix, but they are distinct formats to be parsed)<o:p></o:p></span></li><ul style="margin-top:0in" type="circle">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level2 lfo1"><span lang="EN-CA">Paint(Var)Transform, Paint(Var)Translate, Paint(Var)Scale, Paint(Var)ScaleAroundCenter, Paint(Var)ScaleUniform, Paint(Var)ScaleUniformAroundCenter, Paint(Var)Rotate,
Paint(Var)RotateAroundCenter, Paint(Var)Skew, Paint(Var)SkewAroundCenter<o:p></o:p></span></li></ul>
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span lang="EN-CA">Layers (PaintColrLayers)<o:p></o:p></span></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l0 level1 lfo1"><span lang="EN-CA">Embedding of glyph descriptions via PaintColrGlyph<o:p></o:p></span></li></ul>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">Even without colour references a COLR glyph description is still an acyclic directed graph that needs to be walked, with all the available types of operation to be executed.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">My initial reaction to the COLR w/o CPAL idea is that there’s a fair amount more complexity to be added to monochrome glyph rasterization that might not be desirable for all rasterizer implementations.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">After the AHG meeting, it also occurred to me that this proposal would build in a significant limitation for many _<i>colour</i>_ fonts! I think it’s fair to assume that most colour fonts are intended to also provide
legible monochrome display — i.e., most colour fonts are colour/monochrome hybrids. But in that case, there is a CPAL table present, and so COLR could not be used to provide additional compositing modes for monochrome rendering. IMO, that’s a pretty significant
limitation that we shouldn’t settle for.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA">Peter<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-CA"><o:p> </o:p></span></p>
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