SVG Heatmaps

Currently the color brick area of heatmaps is rendered using data: URLs. This makes it harder to produce high-quality exported images (especially for print) unless you’re careful with how the image is resampled after exporting (difficult to do given that it’s a PNG embedded in an SVG).

Would you consider using SVG instead, at least for zsmooth=false?

I made a quick patch to try this out. With a 50 x 200 brick heatmap, performance seems pretty close. I could turn this into a PR if it would be accepted.

[alexcjohnson]

Thanks @zbjornson. I guess you mean rendering each brick as a separate solid-color rectangle? This could be an interesting mode to have available, but we wouldn’t want it to always turn to SVG when zsmooth=false - aside from performance questions when you get to even larger sizes, I seem to recall some situations where it’s still tricky to get the stitching right when two shapes are expected to exactly meet - for example stacked or gapless bar charts.

@etpinard what do you think, another zsmooth value ('rects'?) or a new attribute (rendering=('image'|'rects') where 'rects' forces zsmooth=false)?

[zbjornson]

@alyst my patch was a super rough one just for benchmarking and is far from usable, sorry. I’ll be revisiting it within the next few months and will post or PR it if I can.

Using SVG rects might fix #888 as well, if the mouse event listeners are placed on the rects directly.