mirror of
https://github.com/dankamongmen/notcurses.git
synced 2024-10-31 15:20:13 +00:00
40 lines
1.5 KiB
Markdown
40 lines
1.5 KiB
Markdown
|
# Hacking!
|
||
|
|
|
||
|
|
## Rows
|
||
|
|
|
||
|
|
There are four kinds of `y`s: physical, rational, logical, and virtual. Physical
|
||
|
|
and rational `y`s are independent of any particular plane. A physical `y`
|
||
|
|
refers to a particular row of the terminal. A rational `y` refers to a particular
|
||
|
|
row of the rendering area. They are related by:
|
||
|
|
|
||
|
|
* physical `y` - margin `top` == rational `y`
|
||
|
|
* rational `y` + margin `top` == physical `y`
|
||
|
|
|
||
|
|
In the absence of a `top` margin, physical `y` == rational `y`.
|
||
|
|
|
||
|
|
Logical and virtual `y`s are relative to a plane (possibly the standard plane).
|
||
|
|
A logical `y` refers to a row of a plane, independent of scrolling. A virtual
|
||
|
|
`y` refers to a row-sized chunk of the plane's framebuffer, which might be
|
||
|
|
mapped to any row within the plane. They are related by:
|
||
|
|
|
||
|
|
* (logical `y` + plane `logrow`) % plane `leny` == virtual `y`
|
||
|
|
* (virtual `y` + plane `leny` - plane `logrow`) % plane `leny` == logical `y`
|
||
|
|
|
||
|
|
All API points expressing a `y`, whether writing it (e.g. `ncplane_cursor_yx()`)
|
||
|
|
or reading it (e.g. `ncplane_cursor_move_yx()`), are working with a logical `y`.
|
||
|
|
The `y` member of an `ncplane` is also a logical `y`.
|
||
|
|
|
||
|
|
Whenever we initiate a write past the end of the line, and the virtual `y` is
|
||
|
|
equal to `ncplane->lenx - 1`, we must scroll. Scrolling:
|
||
|
|
|
||
|
|
* plane `logrow` = (plane `logrow` + 1) % plane `leny`
|
||
|
|
|
||
|
|
As a result, logical `y` is unchanged, but virtual `y` has advanced.
|
||
|
|
|
||
|
|
Virtual `y` is useful for only two things:
|
||
|
|
|
||
|
|
* Determining whether to scroll, and
|
||
|
|
* Indexing into the plane's framebuffer
|
||
|
|
|
||
|
|
Thus we usually keep `y` logical.
|