Can't control tick generation

[chnn]

It's desirable to format ticks using a binary unit prefix when plotting data whose y-value is measured in bytes.

But the y-axis generates tick marks at "nice" intervals, i.e. at powers of 10. These intervals are no longer nice when formatting numbers with a binary unit prefix.

For example, here's the same plot with ticks formatted using a decimal unit prefix:

It has a nice tick of "6G". When formatting the ticks with a binary unit prefix, it looks like this:

The generated tick is now "5.5879G" (6 gigabytes =~ 5.88 gibibytes), which is no longer nice.

[TCL735]

Requirements:

• value axis ticks should allow a step and cover a range using that step

• tooltip's _value unit can be a different scale than the tick labeling. Example: megabytes (or mebibytes) in the tooltip, while gigabytes (or gibibytes) on the tick labels. This allows the user to see precision in the tooltip and broader values by glancing at the axis.

[TCL735]

The previous comment's 2nd point on having different scales for the value axis and tooltip should be broken down into two separate stories.

In this story, we will focus on changes to the axes. A separate story can focus on changes to the tooltip.

[TCL735]

Analysis:

Currently, Giraffe allows xTicks and/or yTicks to be specified. When either property is included in the config, that axis is not calculated by Giraffe. When the specified xTicks and/or yTicks are not in domain of the rendered graph, then that axis becomes unlabeled.

We will keep the above behavior and add two additional properties per axis that is mutually exclusively with the above.

New:
xTickStep and xTotalTicks are mutually exclusive with and subservient to xTicks
yTickStep and yTotalTicks are mutually exclusive with and subservient to yTicks

[TCL735]

There is an existing bug that can be fixed with this issue.

The bug is: when there are no y-axis ticks, the graph is wider because of the lack of margins. Margins were being calculated based on having y-axis ticks. Thus, no y-axis ticks means no margins. And when the graph is wider, the x-axis ticks get "erased" due to being overwritten by the redrawing of the wider graph.

To fix this bug, we will use a sample y-axis tick based on the graph data to calculate the margins when the user specifically selects zero for the number of y-axis ticks.

[TCL735]

There is a second part to this story: Integrate this new feature into ui

[TCL735]

Upon further review, it is better to close this story out. As this story only deals with the Giraffe work, which has been completed, we will open a separate story to track the UI integration work.