Add a sprint button: a setting that makes Link sprint without rolling first, as a toggle or while held.

docs/controls.md

@@ -149,6 +149,10 @@ The game makes its vibration for linear actuators: per side a low and a high ban
 
 The log says which it is when a gamepad is taken: `input: HD rumble available for this gamepad: a Pro Controller, through SDL (rumble_hd = 1)`, or `not available` with the reason; the row on the Controls tab is greyed out for a gamepad that cannot take it. With `rumble_hd = 0` nothing is written to the controller and the line says that its driver is asked once the setting is on. The first report a gamepad gets is logged with its bytes (`input: HD rumble: first report written (left ..., right ...)`); a report the controller or its driver refuses is logged too, and the gamepad then rumbles through its motors again. Frequencies are clamped to what the actuators take (41 to 626 Hz in the low band, 82 to 1253 Hz in the high band) and amplitudes to 0..1, the actuators' safe maximum. `rumble_strength` scales the amplitude (its default, 130, is the game's own: the default is above 100 for the motors' sake, and this path divides by it), `rumble_curve` does not apply, and `rumble = 0` silences this path too. A report is written at most every 15 ms (`rumble_hd_ms`, 5 to 50: raise it if a Bluetooth controller stutters or disconnects with HD rumble on), with the newest value only; a value that holds is written again every 30 ms, and the neutral value goes out when the game stops sending for 250 ms, when another gamepad takes over, when the setting is turned off and when the game exits. While HD rumble is on the game makes no dual-motor rumble call for that gamepad. A DualShock 3 on the direct reader keeps its motors either way.
 
+## Sprint button
+
+On 1.1.1, `NX2NAVI_SPRINT_BUTTON` (`sprint_button`, the *Sprint button* row on the Controls tab, live) gives a button that makes Link sprint without rolling first: `b` (the bottom face button), `l`, `r`, `l3` or `r3`, or `off` (the default). `NX2NAVI_SPRINT_MODE` (`sprint_mode`, the *Sprint mode* row) is `toggle` (the default: a press starts the sprint, the next press ends it) or `hold` (Link sprints while the button is held). Link sprints while his input flags hold the dash input; the set `sprint` of `recomp/patches-v111.txt` calls `runtime/sprint.c` after Link's movement update and the stance update that follows load those flags, and the host functions add the dash input while the sprint is on, so the game's own sprint runs with its speed, animation and camera. A toggled sprint goes on through jumps, slides and landings and ends when Link's state is anything else (an attack, a roll, an item, swimming, climbing, a cutscene), when ZL is held, or after four frames standing still (ninety after a press made while standing, before Link has moved). During play (Link's update ran within the last eight controller polls) the button is kept from the game, so it does not also fire its own action; the bottom button is kept only while Link moves, so it attacks as usual otherwise. In the settings menu, a menu of the game or a cutscene every button keeps its role. `NX2NAVI_SPRINT_PATCH=0` turns the patch set off and hides the rows.
+
 ## Nintendo Switch 2 controllers
 
 Windows does not present the Switch 2 Pro Controller as a gamepad SDL can open (the log says `input: no gamepad`), so it needs a bridge program that wakes it and creates a virtual gamepad, for example one that emulates a DualSense: that gives buttons, rumble, gyro and accelerometer. The log then shows `input: gamepad "DualSense Wireless Controller" ... (rumble, gyro and accelerometer, ...)` and `input: motion sensors on`. Bridges that output a DualShock 4 whose gyro and accelerometer never change give buttons and rumble but no motion. Run one bridge at a time; Steam Input can also claim the controller, so close Steam if the bridge does not find it. With several virtual and real gamepads connected the game follows whichever one is pressed.