Timeline grid widget

[BillyDM]

Build the timeline grid as a widget.

Note that this widget will not actually scroll within a tuix scroll container. Instead, this will just draw the various grid lines as a function of the input data.

When zoomed in far enough, this should show additional detail like beats and beat divisions.

Every beat division is marked with a thin vertical line, every beat is marked with a slightly thicker vertical line, and every 4 beats (1 measure) is marked with an event thicker vertical line.

Every 4 measures (16 beats), the background color of the grid should alternative between two different values of gray.

This widget will take these data points as inputs:

• width and height of the timeline area (in pixels)
• horizontal zoom level (1.0 is default zoom level, < 1.0 is zoomed out, and > 1.0 is zoomed in). Just pick something that feels reasonable for a scale of 1.0 (like around 100 pixels).
• horizontal scroll position (represented in units of beats)
• vertical scroll position (represented in units of pixels)
• list vertical heights of each track/division (in pixels). This is where the horizontal grid lines should be drawn.