externalgraphic files not scaled for Device Pixel Ratio for polygon fills

[richard-thomas]

externalgraphic files are not scaled to take account of Device Pixel Ratio when generating (polygon) fills. This results in patterns appearing very small on high DP ratio devices like iPhone X (dpr = 3.0). This seems to be fixable (I have tested this on both .png files and .svg files) by inserting:
imageRatio *= window.devicePixelRatio;
at line 2152 of sldreader.js (release 0.2.8):
https://developer.mozilla.org/en-US/docs/Web/API/Window/devicePixelRatio
However, if this gave unaccceptable support for older browsers (e.g. pre-IE11), then DEVICE_PIXEL_RATIO from import 'ol/has' could be used. (However, I don't really understand the "require" statements at the top of sldreader.js so wouldn't like to suggest how that could be added).

[ajkopinga]

Good catch. I have refactored the polygon graphic fill logic in PR #89, taking device pixel ratio into account.
I will publish a new version of the library later today.

[ajkopinga]

The fix is now live in SLDReader v0.2.9.