I have an SVG file (that happens to have been generated using QSvgGenerator)
that has this at the start:
<svg width="139.347mm" height="73.3778mm"
So the units are millimeters. During loading by QSvgRenderer, the size of the
image is initialized from those values by a process that includes this:
// this should really be called convertToDefaultCoordinateSystem
// and convert when type != QSvgHandler::defaultCoordinateSystem
static qreal convertToPixels(qreal len, bool , QSvgHandler::LengthType type)
{
switch (type) {
case QSvgHandler::LT_PERCENT:
break;
case QSvgHandler::LT_PX:
break;
case QSvgHandler::LT_PC:
break;
case QSvgHandler::LT_PT:
return len * 1.25;
break;
case QSvgHandler::LT_MM:
return len * 3.543307;
break;
case QSvgHandler::LT_CM:
return len * 35.43307;
break;
case QSvgHandler::LT_IN:
return len * 90;
break;
case QSvgHandler::LT_OTHER:
break;
default:
break;
}
return len;
}
This implies that the default coordinate system is one in which a unit is 1/90
inch. The fact that LT_PX units are not scaled seems to indicate that unitless
<svg width height> values will be interpreted as if the system is 90 DPI. My
reading here: http://www.w3.org/TR/SVG/coords.html#Units seems to indicate that
unitless width and height should indicate some sort of "pixels".
This seems wrong. It seems likely that the 90 DPI thing comes from
http://www.w3.org/TR/SVG/coords.html#Units where 90 DPI is used *as an
example*. But maybe it's I that is wrong- is there somewhere in the SVG
standard that indicates that these should be interpreted at 90 DPI units?
So, finally, my questions:
1) Am I right that this is wrong?
2) If it is just an assumption used to produce a consistent answer internally,
then can I assume that QSvgRenderer::defaultSize() will always embody that
assumption? If so, then I can scale my pictures based on a 90 DPI unit and be
assured that it will always be that way.
-John Weeks
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