21b5389bbe
Add a simple tap counting filter for boolean streams.
The filter activates when the input has risen (transitioned from false
to true, like when a button is tapped) the required number of times
within the time window after the first rising edge. Once activated, the
output remains true as long as the input is true. The tap count resets
when the time window expires or when the input goes false after
activation.
Example usage:
```java
xbox.a()
.multiPress(2, 0.2) // Detect a double tap within 0.2 seconds
.onTrue(Commands.print("Double tapped A button"));
xbox.y()
.multiPress(2, 0.5) // Detect a double tap within 0.5 seconds
.whileTrue(Commands.print("Y held after tap").repeatedly());
```
This is not a noise reduction and/or input smoothing filter, but it is
similar in usage to debounce, so I believe it could be considered a
filter, but am open to a better location.
I believe this would be a useful addition, as double/triple tapping a
button is a common control option in games, yet is not often utilized by
newer FRC teams. I believe adding it to WPILib in a standard way will
allow more teams to make the most out of their controls.
wpimath
wpimath contains utilities for robot control (feedforward/feedback), state estimation (filters, Kalman and otherwise), 2D/3D geometry, kinematics, trajectory generation, and trajectory optimization.
Implementation guidelines
A lot of wpimath features directly implement equations from books or papers. The following guidelines make that code easier to maintain and audit for correctness.
Citations
Cite source books/papers at the top of the function (e.g., See section 5.6 of "book name".). If multiple items from a given work are referenced, write a bibliography entry for the work to reference later.
Cite the equation numbers each line of code implements, if applicable. For example, See equation (#.#) of [1]. where [1] is a bibliography reference number.
Comments
Comment each line of code with its pretty-printed math equivalent.
// xₖ₊₁ = Axₖ + Buₖ
x = A * x + B * u;
Link to explanatory material where appropriate to explain background knowledge and/or notation choice.
Variable naming
Follow established mathematical convention where possible (e.g., use A, B, C, D for state-space notation instead of stateTransitionMatrix).
Use math symbols in variable names (see Unicodeit) to match source papers. This usually entails some Greek letters (α), but diacritics, superscripts, and subscripts need to be spelled out (ẋ → x_dot, αₖ² → α_k_sq) since compilers reject them, and the small features make variable names difficult to read.
Derivations
Put small derivations in comments within the function. Put large derivations in algorithms.md and link to them.
Unicodeit
When writing math expressions in documentation, use https://www.unicodeit.net/ to convert LaTeX to a Unicode equivalent that's easier to read. Not all expressions will translate (e.g., superscripts of superscripts) so focus on making it readable by someone who isn't familiar with LaTeX. If content on multiple lines needs to be aligned in Doxygen/Javadoc comments (e.g., integration/summation limits, matrices packed with square brackets and superscripts for them), put them in @verbatim/@endverbatim blocks in Doxygen or <pre> tags in Javadoc so they render with monospace font.
The LaTeX to Unicode conversions can also be done locally via the unicodeit Python package. To install it, execute:
pip install --user unicodeit
Here's example usage:
$ python -m unicodeit.cli 'x_{k+1} = Ax_k + Bu_k'
xₖ₊₁ = Axₖ + Buₖ
On Linux, this process can be streamlined further by adding the following Bash function to your .bashrc (requires wl-clipboard on Wayland or xclip on X11):
# Converts LaTeX to Unicode, prints the result, and copies it to the clipboard
uc() {
if [ $WAYLAND_DISPLAY ]; then
python -m unicodeit.cli $@ | tee >(wl-copy -n)
else
python -m unicodeit.cli $@ | tee >(xclip -sel)
fi
}
Here's example usage:
$ uc 'x_{k+1} = Ax_k + Bu_k'
xₖ₊₁ = Axₖ + Buₖ