Fixed bug 4707 - SDL_SetRelativeMouseMode fails on Vivante

Cameron Gutman

The bugfix in https://hg.libsdl.org/SDL/rev/ca9417a52f18 caused SDL_SetRelativeMouseMode() to begin failing on Vivante (Steam Link). Even though Vivante doesn't have a SetRelativeMouseMode() or WarpMouse() function, it's in relative mode already (because it uses evdev) so the function was actually working as intended.

I think providing a no-op SetRelativeMouseMode() function for Vivante is a reasonable fix. Since it's already getting relative events through evdev, it really is a no-op to "enter relative mode".

In fact, this is probably the right thing to do for all backends that use evdev (vivante, raspberry, and kmsdrm). Raspberry and kmsdrm both have WarpMouse() implementations so SDL_SetRelativeMouseMode() isn't failing there, but it still seems to make sense not to have to do the fake warping if they're evdev-based anyway.

Xcode-iOS/SDL/SDL.xcodeproj/project.pbxproj

@@ -129,6 +129,14 @@ static Uint8 EVDEV_MouseButtons[] = {
     SDL_BUTTON_X2 + 3           /*  BTN_TASK        0x117 */
 };
 
+static int
+SDL_EVDEV_SetRelativeMouseMode(SDL_bool enabled)
+{
+    /* Mice already send relative events through this interface */
+    return 0;
+}
+
+
 int
 SDL_EVDEV_Init(void)
 {
@@ -162,6 +170,8 @@ SDL_EVDEV_Init(void)
         _this->kbd = SDL_EVDEV_kbd_init();
     }
 
+    SDL_GetMouse()->SetRelativeMouseMode = SDL_EVDEV_SetRelativeMouseMode;
+
     _this->ref_count += 1;
 
     return 0;