emscripten: Decrease vertical scroll speed by using deltaMode Reference issue #4623.
diff --git a/src/video/emscripten/SDL_emscriptenevents.c b/src/video/emscripten/SDL_emscriptenevents.c
index 0c1b94c..bae18d2 100644
--- a/src/video/emscripten/SDL_emscriptenevents.c
+++ b/src/video/emscripten/SDL_emscriptenevents.c
@@ -409,7 +409,22 @@ static EM_BOOL
Emscripten_HandleWheel(int eventType, const EmscriptenWheelEvent *wheelEvent, void *userData)
{
SDL_WindowData *window_data = userData;
- SDL_SendMouseWheel(window_data->window, 0, (float)wheelEvent->deltaX, (float)-wheelEvent->deltaY, SDL_MOUSEWHEEL_NORMAL);
+
+ float deltaY = wheelEvent->deltaY;
+
+ switch (wheelEvent->deltaMode) {
+ case DOM_DELTA_PIXEL:
+ deltaY /= 100; /* 100 pixels make up a step */
+ break;
+ case DOM_DELTA_LINE:
+ deltaY /= 3; /* 3 lines make up a step */
+ break;
+ case DOM_DELTA_PAGE:
+ deltaY *= 80; /* A page makes up 80 steps */
+ break;
+ }
+
+ SDL_SendMouseWheel(window_data->window, 0, (float)wheelEvent->deltaX, -deltaY, SDL_MOUSEWHEEL_NORMAL);
return SDL_GetEventState(SDL_MOUSEWHEEL) == SDL_ENABLE;
}