I agree that the current behavior is not good. It hinders distinction in monochrome charts.

The spec (see URL) has no specification for the line height of the legend key of a line.
In OOo3.4 the height follows the line height up to 0.05cm, which is the upper limit. In OOo2.4.3 the legend key line has the same height as the graph line, even when it was larger than the font height, so that the keys could overlap. That was not the best solution.

In Excel and in Gnumeric the key line height follows the graph line thickness up to about 50% of the font size height. In Excel this is done in steps, in Gnumeric it is smooth.

I think, that we should do it similar to Gnumeric, use directly the graph line thickness up to 50% of the font size height.

Because the current spec says nothing about the height of the legend key of a line, first the spec has to be extended. Therefore I set the issue to enhancement.

I see
const sal_Int32 nMaxLineWidthForLegend = 50;/*1/100 mm*///todo: make this dependent from legend entry height
in line 90 in chart2/source/view/main/VLegendSymbolFactory.cxx

I see no easy way to make it dependent on font size.

But I suggest to set the constant to 300 instead of 50. With 300 the line in the legend will correspond to the graphic line up to 0,3cm, which will be enough for all "normal" charts, even in impress. On the other hand it will not exceed font height down to 8.5pt, and for smaller font sizes line width larger than 0,3cm is unlikely.

I have tested it in DEVm100 with the old implementation of the legend and I think it would be a good compromise until the line can be made dependent on font size. But I haven't got an actual build with resizable legend to test it there.

Chart issue...

Created attachment 76402 [details]
Example of the resulting buggy line graph in 3.3.0

getting rid of value "enhancement" for field "severity".
For enhancement the field "issue type" shall be used.