[QGIS-Developer] Issue with determining Symbol size - Bug?

[C Hamilton]

Try running this code. Make sure you have a point layer selected that is
using single symbol symbology. The value that is returned is 0. In my case
the units for the symbol are millimeters and a value of 5. I am using QGIS
3.14.15 on windows.

canvas = iface.mapCanvas()
context = QgsRenderContext.fromMapSettings(canvas.mapSettings())
lyr = iface.activeLayer()
rnd = lyr.renderer()
sym = rnd.symbol()
sym_size = QgsSymbolLayerUtils.estimateMaxSymbolBleed(sym, context)
print(sym_size)

I am not sure what estimateMaxSymbolBleed really does, but it doesn't seem
to represent symbol size.

Thanks,

Calvin



On Thu, Sep 3, 2020 at 7:13 PM Nyall Dawson <nyall.dawson at gmail.com> wrote:

> On Thu, 3 Sep 2020 at 00:06, C Hamilton <adenaculture at gmail.com> wrote:
> >
> > Nyall,
> >
> > Thanks. This almost gets the right answer.
> QgsSymbolLayerUtils::estimateMaxSymbolBleed is returning 0 as its value.
> I'm not sure what the problem is with it. bounds() seems to work for small
> symbols which is probably all I'll need, but if the symbol is very large
> with a large border and join style set to miter, the bounding box it
> returns is a little too small. My example used an excessively large icon
> and large border which probably would not be used in any real project.
>
> Hm - not sure what your issue with estimateMaxSymbolBleed is. Are you
> using data defined properties at all?
>
> Regarding the miter question -- that's something which none of the
> symbol bounds checking functions currently available account for.
>
> Nyall
>
> >
> > Calvin
> >
> > On Tue, Sep 1, 2020 at 6:39 PM Nyall Dawson <nyall.dawson at gmail.com>
> wrote:
> >>
> >> On Wed, 2 Sep 2020 at 03:39, C Hamilton <adenaculture at gmail.com> wrote:
> >> >
> >> > I am trying to calculate the size of a single symbol in pixels using:
> >> >
> >> > canvas = iface.mapCanvas()
> >> > context = QgsRenderContext.fromMapSettings(canvas.mapSettings())
> >> > layer = iface.activeLayer()
> >> > rnd = layer.renderer()
> >> > sym = rnd.symbol()
> >> > scaled_size_in_pixels = context.convertToPainterUnits(
> >> >     sym.size(),
> >> >     sym.sizeUnit(),
> >> >     sym.sizeMapUnitScale() )
> >> >
> >> > The last line can also be calculated by:
> >> >
> >> >   scaled_size_in_pixels = sym.size(context)
> >> >
> >> > I am finding that this is returning the size of the filled area of
> the symbol, but it does not include the border. Is this a bug or do I need
> to add something additional to include the border?
> >>
> >> You can use  QgsSymbolLayerUtils::estimateMaxSymbolBleed if you're
> >> wanting to calculate the "maximum" bounding box of a rendered symbol.
> >> That includes any stroke/offset/other settings which also affect the
> >> rendered bounds.
> >>
> >> There's also QgsMarkerSymbol::bounds which returns an approximate
> >> bounding box of a marker symbol, which also accounts for things like
> >> the stroke and offset.
> >>
> >> Nyall
> >>
> >>
> >> >
> >> > Thanks,
> >> >
> >> > Calvin
> >> >
> >> > _______________________________________________
> >> > QGIS-Developer mailing list
> >> > QGIS-Developer at lists.osgeo.org
> >> > List info: https://lists.osgeo.org/mailman/listinfo/qgis-developer
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>
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