STRUCT FF_ENVELOPE(9)

💖 struct ff_envelope(9) 💖

okay so this is straight out of the Kernel API Manual, section 9, and it's literally the blueprint for making your controller shake with drama — it's the generic force-feedback effect envelope, no cap 🎀

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✨ NAME ✨

struct ff_envelope — the generic force-feedback effect envelope, bestie. it's the thing that decides how hard your rumble starts and how gently it fades out 💅

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🌸 SYNOPSIS 🌸

struct ff_envelope {
    __u16 attack_length;
    __u16 attack_level;
    __u16 fade_length;
    __u16 fade_level;
 };

like, four little fields. four. and they control the whole ~emotional arc~ of your vibration. iconic 🦋

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🎀 Members 🎀

• attack_length — how long the attack lasts, in ms. it's giving "the buildup" ✨
• attack_level — the level right at the beginning of the attack. the opening number, the main character entrance 👑
• fade_length — duration of the fade, in ms. the slow, graceful exit 🌈
• fade_level — the level at the end of the fade. where it all lands 🍓

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💜 Description 💜

okay this is the important bit so pay attention bestie 🫶

attack_level and fade_level are absolute values. when the envelope is actually being applied, the force-feedback core converts them into a positive/negative value — and it does that based on the polarity of the default level of the effect. so like, the core does the math, you just hand it the magnitude ✨

the valid range for the attack and fade levels is 0x0000 - 0x7fff. that's it. that's the range. don't go outside it 🙈

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🔥 SEE ALSO 🔥

kernel file ./include/uapi/linux/input.h, plus the whole friend group:

• struct input_absinfo(9)
• struct input_keymap_entry(9)
• EVIOCGMTSLOTS(9)
• EVIOCGMASK(9)
• EVIOCSMASK(9)
• struct ff_replay(9)
• struct ff_trigger(9)
• struct ff_constant_effect(9)
• struct ff_ramp_effect(9)
• struct ff_condition_effect(9)
• struct ff_periodic_effect(9)
• struct ff_rumble_effect(9)
• struct ff_haptic_effect(9)
• struct ff_effect(9)

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fr fr go read struct ff_effect(9) next, it's the parent friend of this whole situation 💀

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and that's the whole page, bestie! it lives at ./include/uapi/linux, dated October 2026 — so yeah, it's from the future and it still slays 💅✨🌸