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fix: normalize Emscripten wheel events by deltaMode #164

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fix: normalize Emscripten wheel events by deltaMode #164

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27 changes: 23 additions & 4 deletions src/windy/platforms/emscripten/platform.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -555,10 +555,29 @@ proc onMouseMove(eventType: cint, mouseEvent: ptr EmscriptenMouseEvent, userData

proc onWheel(eventType: cint, wheelEvent: ptr EmscriptenWheelEvent, userData: pointer): EM_BOOL {.cdecl.} =
let window = cast[Window](userData)
# Normalize web wheel events to match other platforms.
let normalizedDeltaX = wheelEvent.deltaX.float32
let normalizedDeltaY = wheelEvent.deltaY.float32
window.state.perFrame.scrollDelta += vec2(normalizedDeltaX, normalizedDeltaY)

var x = wheelEvent.deltaX.float32
var y = wheelEvent.deltaY.float32

# Normalize to match native backends (~10 units per scroll notch).
# DOM_DELTA_PIXEL (0): browsers report ~100-120px per notch on Linux.
# DOM_DELTA_LINE (1): browsers report ~3 lines per notch.
# DOM_DELTA_PAGE (2): one full page.
case wheelEvent.deltaMode
of 0: # DOM_DELTA_PIXEL
x *= 0.1'f32
y *= 0.1'f32
of 1: # DOM_DELTA_LINE
x *= 10.0'f32 / 3.0'f32
y *= 10.0'f32 / 3.0'f32
of 2: # DOM_DELTA_PAGE
let pageHeight = max(1'f32, window.size.y.float32 * 0.9'f32)
x *= pageHeight
y *= pageHeight
else:
discard

window.state.perFrame.scrollDelta += vec2(x, y)
if window.onScroll != nil:
window.onScroll()
return 1
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