qmk_firmware/docs/feature_pointing_device.md

Pointing Device

Pointing Device is a generic name for a feature intended to be generic: moving the system pointer arround. There are certainly other options for it - like mousekeys - but this aims to be easily modifiable and lightweight. You can implement custom keys to control functionality, or you can gather information from other peripherals and insert it directly here - let QMK handle the processing for you.

To enable Pointing Device, uncomment the following line in your rules.mk:

POINTING_DEVICE_ENABLE = yes

To manipulate the mouse report, you can use the following functions:

• pointing_device_get_report() - Returns the current report_mouse_t that represents the information sent to the host computer
• pointing_device_set_report(report_mouse_t newMouseReport) - Overrides and saves the report_mouse_t to be sent to the host computer

Keep in mind that a report_mouse_t (here "mouseReport") has the following properties:

• mouseReport.x - this is a signed int from -127 to 127 (not 128, this is defined in USB HID spec) representing movement (+ to the right, - to the left) on the x axis.
• mouseReport.y - this is a signed int from -127 to 127 (not 128, this is defined in USB HID spec) representing movement (+ upward, - downward) on the y axis.
• mouseReport.v - this is a signed int from -127 to 127 (not 128, this is defined in USB HID spec) representing vertical scrolling (+ upward, - downward).
• mouseReport.h - this is a signed int from -127 to 127 (not 128, this is defined in USB HID spec) representing horizontal scrolling (+ right, - left).
• mouseReport.buttons - this is a uint8_t in which the last 5 bits are used. These bits represent the mouse button state - bit 3 is mouse button 5, and bit 7 is mouse button 1.

When the mouse report is sent, the x, y, v, and h values are set to 0 (this is done in "pointing_device_send()", which can be overridden to avoid this behavior). This way, button states persist, but movement will only occur once. For further customization, both pointing_device_init and pointing_device_task can be overridden.

In the following example, a custom key is used to click the mouse and scroll 127 units vertically and horizontally, then undo all of that when released - because that's a totally useful function. Listen, this is an example:

case MS_SPECIAL:
	report_mouse_t currentReport = pointing_device_get_report();
    if (record->event.pressed)
    {
        currentReport.v = 127;
		currentReport.h = 127;
		currentReport.buttons |= MOUSE_BTN1; //this is defined in report.h
    }
    else
    {
        currentReport.v = -127;
        currentReport.h = -127;
        currentReport.buttons &= ~MOUSE_BTN1;
    }
	pointing_device_set_report(currentReport);
    break;

Recall that the mouse report is set to zero (except the buttons) whenever it is sent, so the scrolling would only occur once in each case.