docs: Add initial pointer docs.

docs/docs/config/pointers.md

@@ -0,0 +1,67 @@
+---
+title: Pointer Configuration
+sidebar_label: Pointers
+---
+
+These are settings related to the pointer/mouse support in ZMK.
+
+See [Configuration Overview](index.md) for instructions on how to change these settings.
+
+## Kconfig
+
+Definition file: [zmk/app/mouse/Kconfig](https://github.com/zmkfirmware/zmk/blob/main/app/mouse/Kconfig)
+
+### General
+
+| Config                              | Type | Description                                                                | Default |
+| ----------------------------------- | ---- | -------------------------------------------------------------------------- | ------- |
+| `CONFIG_ZMK_MOUSE`                  | bool | Enable the general pointer/mouse functionality                             | n       |
+| `CONFIG_ZMK_MOUSE_SMOOTH_SCROLLING` | bool | Enable smooth scrolling HID functionality (via HID Resolution Multipliers) | n       |
+
+### Zephyr Settings
+
+The following settings are from Zephyr, and should be defaulted to sane values, but can be adjusted if you encounter problems
+
+| Config                           | Type | Description                                                | Default                         |
+| -------------------------------- | ---- | ---------------------------------------------------------- | ------------------------------- |
+| `CONFIG_INPUT_THREAD_STACK_SIZE` | int  | Stack size for the dedicated input event processing thread | 512 (1024 on split peripherals) |
+
+## Input Listener
+
+TODO: Complete description
+
+### Devicetree
+
+Applies to: `compatible = "zmk,input-listener"`
+
+Definition file: [zmk/app/dts/bindings/zmk,input-listener.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/dts/bindings/zmk%2Cinput-listener.yaml)
+
+| Property           | Type   | Description                                                         | Default |
+| ------------------ | ------ | ------------------------------------------------------------------- | ------- |
+| `device`           | handle | Input device handle                                                 |         |
+| `input-processors` | array  | List of input processors (with parameters) to apply to input events |         |
+
+#### Child Properties
+
+Additional properties can be set on child nodes, which allows changing the settings when certain layers are enabled:
+
+| Property           | Type  | Description                                                                                      | Default |
+| ------------------ | ----- | ------------------------------------------------------------------------------------------------ | ------- |
+| `layers`           | array | List of layer indexes. This config will apply if any layer in the list is active.                |         |
+| `input-processors` | array | List of input processors (with parameters) to apply to input events                              |         |
+| `inherit`          | flag  | Whether to first apply the base input processors before the processors specific to this override |         |
+
+## Input Split
+
+TODO: Complete description
+
+### Devicetree
+
+Applies to: `compatible = "zmk,input-split"`
+
+Definition file: [zmk/app/dts/bindings/zmk,input-split.yaml](https://github.com/zmkfirmware/zmk/blob/main/app/dts/bindings/zmk%2Cinput-split.yaml)
+
+| Property           | Type   | Description                                                         | Default |
+| ------------------ | ------ | ------------------------------------------------------------------- | ------- |
+| `device`           | handle | Input device handle                                                 |         |
+| `input-processors` | array  | List of input processors (with parameters) to apply to input events |         |

docs/docs/development/hardware-integration/pointers.md

@@ -0,0 +1,127 @@
+---
+title: Pointing Devices
+sidebar_label: Pointers
+---
+
+ZMK's pointer support builds upon the Zephyr [input API](https://docs.zephyrproject.org/3.5.0/services/input/index.html) to offer pointer/mouse functionality with various hardware. A limited number of input drivers are available in the Zephyr 3.5 version currently used by ZMK, but additional drivers can be found in [external modules](../../features/modules.mdx) for a variety of hardware.
+
+## Input Device
+
+The starting point to any integration of a physical pointing device is the device node itself. The specifics of where this node goes will depend on the specific hardware. _Most_ pointing hardware uses either SPI or I2C for communication, and will be nested under a properly configured bus node, e.g. `&pro_micro_i2c` or for a complete onboard setup, `&i2c3`. See the documentation on [pin control](./pinctrl.mdx) if you need to configure the pins for an I2C or SPI bus.
+
+For example, if setting up a device that uses SPI, you may have a node like:
+
+```dts
+&pro_micro_spi {
+    status = "okay";
+    cs-gpios = <&pro_micro 19 GPIO_ACTIVE_LOW>;
+
+    glidepoint: glidepoint@0 {
+        compatible = "cirque,pinnacle";
+        reg = <0>;
+        spi-max-frequency = <1000000>;
+        status = "okay";
+        dr-gpios = <&pro_micro 5 (GPIO_ACTIVE_HIGH)>;
+
+        sensitivity = "4x";
+        sleep;
+        no-taps;
+    };
+};
+```
+
+The specifics of the properties required to set for a given driver will vary; always consult the devicetree bindings file for the specific driver to see what properties can be set.
+
+## Listener
+
+Every input device needs an associated listener added that listens for events from the device and processes them before sending the events to the host using a HID mouse report. See [input listener configuration](../../config/pointers.md#input-listener) for the full details. For example, to add a listener for the above device:
+
+```dts
+/ {
+    glidepoint_listener {
+        compatible = "zmk,input-listener";
+        device = <&glidepoint>;
+    };
+};
+```
+
+## Input Processors
+
+Some physical pointing devices may be generating input events that need some adjustment before being sent to hosts. For example a trackpad might be integrated into a keyboard rotated 90° and need the X/Y data adjusted appropriately. This can be accomplished with [input processors](../../keymaps/input-processors/index.md). You could enhande the above listener with:
+
+```dts
+#include <dt-bindings/zmk/input_transform.h>
+
+/ {
+    glidepoint_listener {
+        compatible = "zmk,input-listener";
+        device = <&glidepoint>;
+        input-processors = <&zip_xy_transform (INPUT_TRANSFORM_XY_SWAP | INPUT_TRANSFORM_X_INVERT | INPUT_TRANSFORM_Y_INVERT)>;
+    };
+};
+```
+
+## Split
+
+Pointing devices are supported on split peripherals, with some additional configuration using the [input split];(../../config/pointers.md#input-split). All split pointers are identified using a unique integer value, which is specified using the `reg` property and in the `@#` suffix for the node. If adding multiple peripheral pointers, be sure that each is given a unique identifier.
+
+### Shared
+
+Both peripheral and central make use of a `zmk,input-split` device, which functions differently depending on where is is used. To avoid duplicating work, this node can be defined in a common `.dtsi` file that is included into both central and peripheral `.overlay`/`.dts` files.
+
+:::note
+
+Input splits need to be nested under a parent node that properly sets the `#address-cells` and `#size-cells` values appropriately. These settings are what allow us to use a single integer number for the `reg` value.
+
+:::
+
+```dts
+/ {
+    split_inputs {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        glidepoint_split: glidepoint_split@0 {
+            compatible = "zmk,input-split";
+            reg = <0>;
+        };
+    };
+};
+```
+
+### Peripheral
+
+On the peripheral, first include the shared file, and then update the input split to reference the pointer device that should be proxied:
+
+```dts
+#include "common.dtsi"
+
+&glidepoint_split {
+    device = <&glidepoint>;
+};
+```
+
+If needed, the split can also have basic input processors applied to fix up the input data before it is sent to the central:
+
+```dts
+&glidepoint_split {
+    device = <&glidepoint>;
+
+    input-processors = <&zip_xy_transform (INPUT_TRANSFORM_XY_SWAP | INPUT_TRANSFORM_X_INVERT | INPUT_TRANSFORM_Y_INVERT)>;
+};
+```
+
+### Central
+
+On the central, the input split acts as an input device, receiving events from the peripheral and raising them locally. First, include the shared file, and then add an [input listener](#listener) to the input split:
+
+```dts
+#include "common.dtsi"
+
+/ {
+    glidepoint_listener: glidepoint_listener {
+        compatible = "zmk,input-listener";
+        device = <&glidepoint_split>;
+    };
+};
+```

docs/docs/features/pointers.md

@@ -0,0 +1,33 @@
+---
+title: Pointers
+---
+
+ZMK supports physical pointing devices, as well as [mouse emulation behaviors](../keymaps/behaviors/mouse-emulation.md) for sending HID pointing events to hosts.
+
+## Configuration
+
+To enable the pointer functionality, you must set `CONFIG_ZMK_MOUSE=y` in your config. See the [pointer configuration](../config/pointers.md) for the full details.
+
+:::warning
+
+When enabling the feature, changes are made to the HID report descriptor, which may not get picked up automatically over BLE to some hosts. Be sure to remove and re-pair to your hosts once you enable the feature
+
+:::
+
+## Mouse Emulation
+
+Mouse emulation allows you to use your keyboard as a pointing device without using dedicated pointer hardware, like an integrated trackpad, trackball, etc. By adding new bindings in your keymap like `&mmv MOVE_UP` you can make key presses send mouse HID events to your connected hosts.
+
+See the [mouse emulation behaviors](../keymaps/behaviors/mouse-emulation.md) for details.
+
+## Physical Pointers
+
+There are a few drivers available for supported physical pointing devices integrated into ZMK powered device. When doing so, you can use your device as both a keyboard and a pointing device with any connected hosts. The functionality can be extended further, e.g. slow mode, scroll mode, temporary mouse layers, etc. by configuring input processors linked to the physical pointing device.
+
+## Input Processors
+
+Input processors are small pieces of functionality that process and optionally modify events generated from emulated and physical pointing devices. Processors can do things like scaling movement values to make them larger or smaller for detailed work, swapping the event types to turn movements into scroll events, or temporarily enabling an extra layer while the pointer is in use.
+
+## Input Listeners
+
+Listeners are the key piece that integrate the low level input devices to the rest of the ZMK system. In particular, listeners subscribe to input events from the linked device, and when a given event occurs (e.g. X/Y movement), apply any input processors before sending those events to the HID system for notification to the host. The main way to modify the way a pointer behaves is by configuring the input processors for a given listener.

docs/docs/keymaps/behaviors/mouse-emulation.md

@@ -67,6 +67,16 @@ This example will send press of the fourth mouse button when the binding is trig
 &mkp MB4
 ```
 
+### Input Processors
+
+If you want to apply any [input processors](../input-processors/index.md#input-processors-overview) to `&mkp` you can do so by referencing `&mkp_input_listener`, e.g.:
+
+```dts
+&mkp_input_listener {
+    input-processors = <&zip_temp_layer 2 2000>;
+}
+```
+
 ## Mouse Move
 
 This behavior sends mouse X/Y movement events to the connected host.
@@ -99,6 +109,16 @@ The following will send a left mouse movement event to the host when pressed/hel
 &mmv MOVE_LEFT
 ```
 
+### Input Processors
+
+If you want to apply any [input processors](../input-processors/index.md#input-processors-overview) to `&mmv` you can do so by referencing `&mmv_input_listener`, e.g.:
+
+```dts
+&mmv_input_listener {
+    input-processors = <&zip_temp_layer 2 2000>;
+}
+```
+
 ## Mouse Scroll
 
 This behavior sends vertical and horizontal scroll events to the connected host.
@@ -130,3 +150,13 @@ The following will send a scroll left event to the host when pressed/held:
 ```
 &msc MOVE_LEFT
 ```
+
+### Input Processors
+
+If you want to apply any [input processors](../input-processors/index.md#input-processors-overview) to `&msc` you can do so by referencing `&msc_input_listener`, e.g.:
+
+```dts
+&msc_input_listener {
+    input-processors = <&zip_temp_layer 2 2000>;
+}
+```

docs/docs/keymaps/input-processors/code-mapper.md

@@ -0,0 +1,59 @@
+---
+title: Code Mapper Input Processor
+sidebar_label: Code Mapper
+---
+
+## Overview
+
+The scaler input processor is used to map the code of an event to a new one, e.g. changing a vertical Y movement event into a scroll event.
+
+## Usage
+
+When used, a code mapper takes no parameters, as the code mappings are specified in the definition of the specific mapper instance, e.g.:
+
+```dts
+&zip_xy_to_scroll_mapper
+```
+
+## Pre-Defined Instances
+
+Three pre-defined instance of the code mapper input processor are available:
+
+| Reference                  | Description                                                                                                                                  |
+| -------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
+| `&zip_xy_to_scroll_mapper` | Map X/Y movement events to horizontal wheel/wheel events, respectively.                                                                      |
+| `&zip_xy_swap_mapper`      | Map X to Y, and Y to X for movements. This can also be accomplished with the [transformer](transformer.md#pre-defined-instances) processors. |
+
+## User Defined Instances
+
+Users can define new instances of the code mapper input processor if they want to target different codes.
+
+### Example
+
+```dts
+#include <zephyr/dt-bindings/input/input-event-codes.h>
+
+/ {
+    input_processors {
+        zip_click_to_middle_click_mapper: zip_click_to_middle_click_mapper {
+            compatible = "zmk,input-processor-code-mapper";
+            #input-processor-cells = <0>;
+            type = <INPUT_EV_KEY>;
+            map = <INPUT_BTN_0 INPUT_BTN_2>;
+        };
+    };
+}
+```
+
+### Compatible
+
+The code mapper input processor uses a `compatible` property of `"zmk,input-processor-code-mapper"`.
+
+### Standard Properties
+
+- `#input-processor-cells` - required to be constant value of `<0>`.
+
+### User Properties
+
+- `type` - The [type](https://github.com/zmkfirmware/zephyr/blob/v3.5.0%2Bzmk-fixes/include/zephyr/dt-bindings/input/input-event-codes.h#L25) of events to scale. Usually, this is `INPUT_EV_REL` for relative events and `INPUT_EV_KEY` for key/button events.
+- `map` - The specific codes of the given type to map, e.g. [relative event codes](https://github.com/zmkfirmware/zephyr/blob/v3.5.0%2Bzmk-fixes/include/zephyr/dt-bindings/input/input-event-codes.h#L245). This list must be an even number of entries, which is process as a list of pairs of codes, with the first is the source code, and the second is the code to map it to.

docs/docs/keymaps/input-processors/index.md

@@ -0,0 +1,50 @@
+---
+title: Input Processor Overview
+sidebar_label: Overview
+---
+
+# Input Processors Overview
+
+"Input processors" are small pieces of functionality that process and optionally modify events generated from emulated and physical pointing devices. Processors can do things like scaling movement values to make them larger or smaller for detailed work, swapping the event types to turn movements into scroll events, or temporarily enabling an extra layer while the pointer is in use.
+
+## Usage
+
+For information on using input processors with a given pointing device, see [input processor usage](usage.md).
+
+# Available Processors
+
+Below is a summary of pre-defined input processors and user-definable input processors available in ZMK, with references to documentation pages describing them.
+
+## Pre-Defined Processors
+
+A set of predefined input processors is available by adding the following at the top of your keymap/overlay file:
+
+```
+#include <input/processors.dtsi>
+```
+
+Once included, you can use the following:
+
+| Binding                    | Processor                                                   | Description                                                         |
+| -------------------------- | ----------------------------------------------------------- | ------------------------------------------------------------------- |
+| `&zip_xy_scaler`           | [XY Scaler](scaler.md#pre-defined-instances)                | Scale a the X/Y input events using a multiplier and divisor         |
+| `&zip_x_scaler`            | [X Scaler](scaler.md#pre-defined-instances)                 | Scale a the X input events using a multiplier and divisor           |
+| `&zip_y_scaler`            | [Y Scaler](scaler.md#pre-defined-instances)                 | Scale a the Y input events using a multiplier and divisor           |
+| `&zip_xy_transform`        | [XY Transform](transformer.md#pre-defined-instances)        | Transform X/Y values, e.g. inverting or swapping                    |
+| `&zip_scroll_transform`    | [Scroll Transform](transformer.md#pre-defined-instances)    | Transform wheel/horizontal wheel values, e.g. inverting or swapping |
+| `&zip_xy_to_scroll_mapper` | [XY To Scroll Mapper](code-mapper.md#pre-defined-instances) | Map X/Y values to scroll wheel/horizontal wheel events              |
+| `&zip_xy_swap_mapper`      | [XY Swap Mapper](code-mapper.md#pre-defined-instances)      | Swap X/Y values                                                     |
+| `&zip_temp_layer`          | [Temporary Layer](temp-layer.md#pre-defined-instances)      | Temporarily enable a layer during pointer use                       |
+
+## Used-Defined Processors
+
+Several of the input processors that have predefined instances, e.g. `&zip_xy_scaler` or `&zip_xy_to_scroll_mapper` can also have new instances created with custom properties around which input codes to scale, or which codes to map, etc.
+
+| Compatible                        | Processor                                            | Description                                      |
+| --------------------------------- | ---------------------------------------------------- | ------------------------------------------------ |
+| `zmk,input-processor-transform`   | [Transform](transformer.md#user-defined-instances)   | Perform various transforms like inverting values |
+| `zmk,input-processor-code-mapper` | [Code Mapper](code-mapper.md#user-defined-instances) | Perform various transforms like inverting values |
+
+## External Processors
+
+Much like behaviors, custom input processors can also be added to [external modules](../../features/modules.mdx) to allow complete control of the processing operation. See [`input_processor.h`](https://github.com/zmkfirmware/zmk/blob/main/app/include/drivers/input_processor.h) for the definition of the driver API.