diff options
| -rw-r--r-- | src/jstk_axis.c | 57 |
1 files changed, 55 insertions, 2 deletions
diff --git a/src/jstk_axis.c b/src/jstk_axis.c index 95ebfe9..cb4a004 100644 --- a/src/jstk_axis.c +++ b/src/jstk_axis.c @@ -82,9 +82,62 @@ jstkAxisTimer(OsTimerPtr timer, /* Calculate scale value, so we get a range from 0 to 32768 */ scale = (32768.0f / (float)(32768 - axis->deadzone)); + /* NOTE: joysticks with a rectangular field have a + * corner position of (32768,32768), joysticks with a + * circular field have (23170,23170). + * + * make sure that diagonal movement feels fast. either: + * 1) linear + * + * f(32768) ~= f(23170) + f(23170) + * f(32768) ~= a * f(23170) + * a = 2.0 + * + * on circular joysticks, the time needed for xy movement is + * exactly the time needed for x + the time for y separately. + * absolute diagonal travel speed (in cm/s) is 0.707 times as fast, + * which feels pretty slow. + * + * on square joysticks, diagonal travel speed is always 1.41 times + * faster than orthogonal travel speed. time needed for diagonal + * movement is always 0.5 times as long as for orthogonal movement. + * + * the value of a = 2.0 results in a nice, non-linear acceleration. + * + * or + * 2) trigonometric + * + * f(32768) ~= sqrt(f(23170)^2 + f(23170)^2)) + * f(32768) ~= a * f(23170) + * a = 1.414 + * + * on circular joysticks, the absolute pointer travel speed + * (in cm/s) is now the same for both linear and diagonal movement, + * which feels natural. moving diagonally takes 0.707 times the time + * of moving orthogonally. + * + * on square joysticks, values are as in 1) + * + * the value of a = 1.414 results in linear acceleration, which feels + * too slow. + * + * to maintain non-linear acceleration, make sure that: + * + * a >>= 1.414 + * + * the following formula achieves results inbetween, + * so it should feel natural on both devices while maintaining a + * nice acceleration: + * + * f(32768) ~= 1.620 * f(23170) + * + * TODO: make this simpler by using only values -1.0..1.0 and + * provide acceleration graphs. + */ + /* How many pixels should this axis move the cursor */ - p1 = ((pow((abs((float)axis->value) - (float)axis->deadzone) * - scale / 1700.0f, 3.4f)) + 100.0f) * + p1 = (pow((abs((float)axis->value) - (float)axis->deadzone) * + scale / 23, 1.4f) + 100.0f) * ((float)NEXTTIMER / 40000.0f); /* How many "pixels" should this axis scroll */ p2 = ((pow((abs((float)axis->value) - (float)axis->deadzone) * |