Create New Function for Coordinate Conversion

[WilliamHYZhang]

It would be beneficial to have a function that simply converts coordinate points to absolute points on the image, and use that function for all the annotations and other applications that will eventually use them.

From @KarthikRIyer:

Yes I suppose you could generalize this conversion. You would always need the output to be in image space so you could have a function that takes in a point, the plot dimensions the input coordinate system and returns the point in the specified output coordinate system.
If this function is to be used by the plots too then it would be better to put it under HelperFunctions.
It would be better to discuss this with others before moving forward. @odmir @karwa?

I hope that I'll be able to work on implementing this soon once the idea is ironed out.

[WilliamHYZhang]

Currently, I'm planning on writing out the function in HelperFunctions and rolling it to only the annotations at first. Later, we can see if the other files would benefit from this as well.

[KarthikRIyer]

@WilliamHYZhang you can move forward with writing the function. We'll definitely need it for the annotations. We can decide later if we should replace it in the Plots. Create an overload for the functions to use just one point or an array of points. If we want to use it for plots, we don't wan't a large number of function invocations in case there are many points to process.

[karwa]

The thing about a helper function is that we don't actually know where the plot will be until we lay it all out; and depends on things like whether you have axis labels on/off. We actually have several useful coordinate systems. For example, matplotlib defines 9 of them:

'figure points'   : points from the lower left corner of the figure
'figure pixels'   : pixels from the lower left corner of the figure
'figure fraction' : 0,0 is lower left of figure and 1,1 is upper, right
'axes points'     : points from lower left corner of axes
'axes pixels'     : pixels from lower left corner of axes
'axes fraction'   : 0,0 is lower left of axes and 1,1 is upper right
'offset points'   : Specify an offset (in points) from the xy value
'offset pixels'   : Specify an offset (in pixels) from the xy value
'data'            : use the axes data coordinate system

From: https://matplotlib.org/gallery/text_labels_and_annotations/annotation_demo.html#specifying-text-points-and-annotation-points

I think it might make sense for us to define a CoordinateSpace enum with similar coordinate spaces, and a Coordinate type which holds a Point and CoordinateSpace. Then the GraphLayout would resolve these in to absolute positions and offsets for the renderer.

[WilliamHYZhang]

Thanks for the comments, will work on implementation. 👍

[WilliamHYZhang]

Ok, so instead of taking in a Point as the location argument, we would take a Coordinate instead. We than make the draw function have an additional argument, point, which will be passed through GraphLayout after it resolves the Coordinate into absolute positions.

[WilliamHYZhang]

Actually, I think we can just overwrite the location in GraphLayout. Will add this as a requirement in the Annotation protocol.

EDIT: just realized that some annotations don't have location, for example arrow, which has start and end of type Point. Maybe we can change this location to an array of Points instead, and GraphLayout will resolve all of them appropriately?

[WilliamHYZhang]

Please continue discussion at #88