Haptic: DInput's POLAR direction actually matches Linux's direction.

Thanks, Elias!

Partially fixes Bugzilla #2686.

include/SDL_haptic.h

@@ -370,7 +370,7 @@ typedef struct _SDL_Haptic SDL_Haptic;
                          ^
                          |
                          |
-    (1,0)  West <----[ HAPTIC ]----> East (-1,0)
+   (-1,0)  West <----[ HAPTIC ]----> East (1,0)
                          |
                          |
                          v
@@ -395,9 +395,9 @@ typedef struct _SDL_Haptic SDL_Haptic;
  *  (X axis, Y axis and Z axis (with 3 axes)).  ::SDL_HAPTIC_CARTESIAN uses
  *  the first three \c dir parameters.  The cardinal directions would be:
  *   - North:  0,-1, 0
- *   - East:  -1, 0, 0
+ *   - East:   1, 0, 0
  *   - South:  0, 1, 0
- *   - West:   1, 0, 0
+ *   - West:  -1, 0, 0
  *
  *  The Z axis represents the height of the effect if supported, otherwise
  *  it's unused.  In cartesian encoding (1, 2) would be the same as (2, 4), you

src/haptic/linux/SDL_syshaptic.c

@@ -671,7 +671,7 @@ SDL_SYS_ToDirection(Uint16 *dest, SDL_HapticDirection * src)
                         180 deg -> 0x8000 (up)
                         270 deg -> 0xC000 (right)
                     */
-        tmp = (((18000 + src->dir[0]) % 36000) * 0xFFFF) / 36000; /* convert to range [0,0xFFFF] */
+        tmp = ((src->dir[0] % 36000) * 0x8000) / 18000; /* convert to range [0,0xFFFF] */
         *dest = (Uint16) tmp;
         break;
 
@@ -682,10 +682,10 @@ SDL_SYS_ToDirection(Uint16 *dest, SDL_HapticDirection * src)
                 Polar direction, except that we have to add 90 degrees. It is the angle
                 from EAST {1,0} towards SOUTH {0,1}.
                 --> add 9000
-                --> finally add 18000 and convert to [0,0xFFFF] as in case SDL_HAPTIC_POLAR.
+                --> finally convert to [0,0xFFFF] as in case SDL_HAPTIC_POLAR.
             */
             tmp = ((src->dir[0]) + 9000) % 36000;    /* Convert to polars */
-        tmp = (((18000 + tmp) % 36000) * 0xFFFF) / 36000; /* convert to range [0,0xFFFF] */
+        tmp = (tmp * 0x8000) / 18000; /* convert to range [0,0xFFFF] */
         *dest = (Uint16) tmp;
         break;
 
@@ -699,10 +699,10 @@ SDL_SYS_ToDirection(Uint16 *dest, SDL_HapticDirection * src)
                         have the first spherical value. Therefore we proceed as in case
                         SDL_HAPTIC_SPHERICAL and add another 9000 to get the polar value.
                       --> add 45000 in total
-                      --> finally add 18000 and convert to [0,0xFFFF] as in case SDL_HAPTIC_POLAR.
+                      --> finally convert to [0,0xFFFF] as in case SDL_HAPTIC_POLAR.
                     */
-                tmp = (((int) (f * 18000. / M_PI)) + 45000) % 36000;
-        tmp = (((18000 + tmp) % 36000) * 0xFFFF) / 36000; /* convert to range [0,0xFFFF] */
+                tmp = (((Sint32) (f * 18000. / M_PI)) + 45000) % 36000;
+        tmp = (tmp * 0x8000) / 18000; /* convert to range [0,0xFFFF] */
         *dest = (Uint16) tmp;
         break;