High resolution scrolling (without feature report parsing) (#24423)

* hires scrolling without feature report parsing

* fix valid range for exponent

* fix incorrect minimum exponent value documentation

1 files changed, 26 insertions, 0 deletions

diff --git a/docs/features/pointing_device.md b/docs/features/pointing_device.md
index 0ecf82c8df..a139df9dc4 100644
--- a/docs/features/pointing_device.md
+++ b/docs/features/pointing_device.md
@@ -419,6 +419,32 @@ The `POINTING_DEVICE_CS_PIN`, `POINTING_DEVICE_SDIO_PIN`, and `POINTING_DEVICE_S
 Any pointing device with a lift/contact status can integrate inertial cursor feature into its driver, controlled by `POINTING_DEVICE_GESTURES_CURSOR_GLIDE_ENABLE`. e.g. PMW3360 can use Lift_Stat from Motion register. Note that `POINTING_DEVICE_MOTION_PIN` cannot be used with this feature; continuous polling of `get_report()` is needed to generate glide reports.
 :::
 
+## High Resolution Scrolling
+
+| Setting                                  | Description                                                                                                               | Default       |
+| ---------------------------------------- | ------------------------------------------------------------------------------------------------------------------------- | ------------- |
+| `POINTING_DEVICE_HIRES_SCROLL_ENABLE`    | (Optional) Enables high resolution scrolling.                                                                             | _not defined_ |
+| `POINTING_DEVICE_HIRES_SCROLL_MULTIPLIER`| (Optional) Resolution mutiplier value used by high resolution scrolling. Must be between 1 and 127, inclusive.            | `120`         |
+| `POINTING_DEVICE_HIRES_SCROLL_EXPONENT`  | (Optional) Resolution exponent value used by high resolution scrolling. Must be between 0 and 127, inclusive.             | `0`           |
+
+The `POINTING_DEVICE_HIRES_SCROLL_ENABLE` setting enables smooth and continuous scrolling when using trackballs or high-end encoders as mouse wheels (as opposed to the typical stepped behavior of most mouse wheels).
+This works by adding a resolution multiplier to the HID descriptor for mouse wheel reports, causing the host computer to interpret each wheel tick sent by the keyboard as a fraction of a normal wheel tick.
+The resolution multiplier is set to `1 / (POINTING_DEVICE_HIRES_SCROLL_MULTIPLIER * (10 ^ POINTING_DEVICE_HIRES_SCROLL_EXPONENT))`, which is `1 / 120` by default.
+If even smoother scrolling than provided by this default value is desired, first try using `#define POINTING_DEVICE_HIRES_SCROLL_EXPONENT 1` which will result in a multiplier of `1 / 1200`.
+
+The function `pointing_device_get_hires_scroll_resolution()` can be called to get the pre-computed resolution multiplier value as a `uint16_t`.
+
+::: warning
+High resolution scrolling usually results in larger and/or more frequent mouse reports. This can result in overflow errors and overloading of the host computer's input buffer. 
+To deal with these issues, define `WHEEL_EXTENDED_REPORT` and throttle the rate at which mouse reports are sent.
+:::
+
+::: warning
+Many programs, especially those that implement their own smoothing for scrolling, don't work well when they receive simultaneous vertical and horizontal wheel inputs (e.g. from high resolution drag-scroll using a trackball).
+These programs typically implement their smoothing in a way that assumes the user will only scroll in one axis at a time, resulting in slow or jittery motion when trying to scroll at an angle.
+This can be addressed by snapping scrolling to one axis at a time.
+:::
+
 ## Split Keyboard Configuration
 
 The following configuration options are only available when using `SPLIT_POINTING_ENABLE` see [data sync options](split_keyboard#data-sync-options). The rotation and invert `*_RIGHT` options are only used with `POINTING_DEVICE_COMBINED`. If using `POINTING_DEVICE_LEFT` or `POINTING_DEVICE_RIGHT` use the common configuration above to configure your pointing device.