Artifacts in plant_nursery pattern

[kocio-pl]

Follow up to #2759 (comment).

Current plant_nursery pattern is not regular - there are subtle artifacts (some rows and columns are bit wider):

It's visible in pattern generator with current settings:

http://www.imagico.de/map/jsdotpattern.php#x,128,jdp32360;gv,6,32,32;rd,1,0,0,pixel,0.125,4,4,0,jdp23814,749d6c,aedea3

Changing distance from 6 to 8 seems to be enough to get rid of this effect:

http://www.imagico.de/map/jsdotpattern.php#x,128,jdp32360;gv,8,32,32;rd,1,0,0,pixel,0.125,4,4,0,jdp23814,749d6c,aedea3

The question is if it would be safe to produce SVG version or just recreate PNG image with a fixed pattern?

[sommerluk]

some rows and columns are bit wider

This is because 6 (the distance) is not a divisor 128 (the pattern size), so obviously using 8 as distance fixes this. This is independent of #2750 and applies to both SVG and PNG.

As rendering is pixel-aligned and the symbol is a simple pixel, this pattern might likely work as SVG.

[kocio-pl]

Makes sense now... 😄

PNG (distance 6)->SVG (distance 8), z19 (click to see full size images)

Before

After

[kocio-pl]

Well, no SVG this time, since it also uses gamma (like an orchard):

openstreetmap-carto/landcover.mss

Lines 161 to 173 in dbc633a

	[feature = 'landuse_plant_nursery'] {
	[zoom >= 10] {
	polygon-fill: @orchard;
	[way_pixels >= 4] { polygon-gamma: 0.75; }
	[way_pixels >= 64] { polygon-gamma: 0.3; }
	}
	[zoom >= 14] {
	polygon-pattern-file: url('symbols/plant_nursery.png');
	polygon-pattern-alignment: global;
	[way_pixels >= 4] { polygon-pattern-gamma: 0.75; }
	[way_pixels >= 64] { polygon-pattern-gamma: 0.3; }
	}
	}

[kocio-pl]

Closing this as a small problem which I'm not going to investigate deeper at the moment. It can be reopened if needed, of course.