Emulate tablet-class pen capabilities for osu!lazer input

[sciboy12]

Motivation

• Make the virtual uinput device present as a real pen/tablet so libinput/osu!lazer treat it as a pen device rather than a generic ABS mouse.
• Ensure the device exposes pressure, pen tool identity and SYN-frame batched updates so modern input stacks accept and correctly interpret events.

Description

• Updated init_uinput() to advertise pen/tablet features by enabling BTN_TOOL_PEN, BTN_TOUCH, ABS_PRESSURE, and INPUT_PROP_DIRECT, and set ABS_PRESSURE range to 0..8191.
• Added emit_pen_tool_state() and call it each active-loop iteration to continuously signal BTN_TOOL_PEN=1 with a SYN_REPORT so the OS sees a pen tool present.
• Reworked ABS handling to cache ABS_X/ABS_Y values and only call emit_abs_delta(x, y, true, true) at a SYN-frame boundary (EV_SYN/SYN_REPORT) when both axes are available, preventing per-axis immediate emission.
• Changed BTN_LEFT handling to mirror contact onto BTN_TOUCH and emit BTN_LEFT + BTN_TOUCH + SYN_REPORT in a single batched write, and added internal pressure/is_down tracking for future pressure emission.

Testing

• Attempted to build with cd /workspace/Abs-C && make, but the build failed in this environment due to missing development headers (ini.h and cjson/cJSON.h), so full compile/runtime validation could not be completed.

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Emit movement when either axis changes per frame

Many evdev tablets emit only the axis that changed before SYN_REPORT (e.g., pure horizontal movement can be ABS_X only). The new if (got_x && got_y) condition drops those frames, so single-axis motion is not forwarded until the other axis changes, which makes the cursor stall or jump and is a functional regression from the previous x_dirty || y_dirty behavior.

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