Raster positioning

[roelandschoukens]

Hi,

I was trying to rasterize some color bar in 1 dimension and display it as a raster mark. The aim was eventually to have a raster with a width matching the plot, a small height (set to 3 pixels in the example, but could be 1 pixel), and correct alignment of data points on the X axis.

How is the positioning of raster marks determined? I’m starting with the documentation page at Observable: (https://observablehq.com/plot/marks/raster#raster-options).

And I don't think the behavior exactly matches the documentation:

If width is specified, x1 defaults to 0 and x2 defaults to width; likewise, if height is specified, y1 defaults to 0 and y2 defaults to height. Otherwise, if data is specified, x1, y1, x2, and y2 respectively default to the frame’s left, top, right, and bottom coordinates. Lastly, if data is not specified […]

examples here: https://observablehq.com/d/8084ece3d437fd56

In example 1, width and height are specified. The documentation suggests the first sentence applies, however the behavior matches the next sentence (the raster covers the entire frame).

Example 2 omits width. This does not affect the positioning but gives us a raster of the desired resolution.

Example 3 omits y. Compared to example 1, this affects the extent of the raster on the Y axis, and it now covers the (0, 3) interval (i.e. 0 and height) as suggested by the documentation.

Example 4 omits both y and width. Compare to example 2 which specifies y and omits width. It is a bit surprising that omitting y affects the positioning on the X axis. Although I think it would be fair enough to argue that y should be specified if data is given.

[Fil]

related to https://talk.observablehq.com/t/axis-color-bar/10344/3