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internal/gamepaddb: fix mapping support for e.g. dpleft:-a0. (#2335)

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SDL interprets this as "map -1 to 1, map 0 to -1", so we should do the same.

This fix contains two parts:
* Fix the intended output range.
* Also fix the formula to map a range to a range.
The fix does not change behavior if a "-a" mapping isn't used, as in any other case max-min == 1 or max+min == 0.

Fixes #2334
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divVerent 2022-09-19 11:34:46 -04:00 committed by GitHub
parent c4ff7ef480
commit 47de8027b9
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1 changed files with 18 additions and 2 deletions
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20
internal/gamepaddb/gamepaddb.go
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@ -228,14 +228,30 @@ func parseMappingElement(str string) (*mapping, error) {
if str[0] == '+' {
numstr = str[2:]
// Only use the positive half, i.e. 0..1.
min = 0
} else if str[0] == '-' {
numstr = str[2:]
max = 0
// Only use the negative half, i.e. -1..0,
// but invert the sense so 0 does not "press" buttons.
//
// In other words, this is the same as '+' but with the input axis
// value reversed.
//
// See SDL's source:
// https://github.com/libsdl-org/SDL/blob/f398d8a42422c049d77c744658f1cd2bb011ed4a/src/joystick/SDL_gamecontroller.c#L960
min, max = 0, min
}
// Map min..max to -1..+1.
//
// See SDL's source:
// https://github.com/libsdl-org/SDL/blob/f398d8a42422c049d77c744658f1cd2bb011ed4a/src/joystick/SDL_gamecontroller.c#L276
// then simplify assuming output range -1..+1.
//
// Yields:
scale := 2 / (max - min)
offset := -(max + min)
offset := -(max + min) / (max - min)
if tilda {
scale = -scale
offset = -offset