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Fix ImGui mouse position when render resolution is different than window resolution #979

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Dec 12, 2024
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Fix ImGui mouse position when render resolution is different than window resolution #979

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54 changes: 37 additions & 17 deletions src/imgui_impl/win32.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -325,16 +325,39 @@ static void ImGui_ImplWin32_UpdateKeyModifiers()
io.AddKeyEvent(ImGuiMod_Super, IsVkDown(VK_LWIN) || IsVkDown(VK_RWIN));
}

// CET: Scale to make sure coords are correct (fixes issues in fullscreen).
static ImVec2 CET_GetScaleFactor()
{
ImGui_ImplWin32_Data* bd = ImGui_ImplWin32_GetBackendData();
ImGuiIO& io = ImGui::GetIO();
IM_ASSERT(bd->hWnd != 0);

if (io.DisplaySize.x == 0.0f || io.DisplaySize.y == 0.0f)
return {-1.0f, -1.0f};

RECT clientRect;
::GetClientRect(bd->hWnd, &clientRect);
return {io.DisplaySize.x / (clientRect.right - clientRect.left), io.DisplaySize.y / (clientRect.bottom - clientRect.top)};
}

// This code supports multi-viewports (multiple OS Windows mapped into different Dear ImGui viewports)
// Because of that, it is a little more complicated than your typical single-viewport binding code!
static void ImGui_ImplWin32_UpdateMouseData(SIZE aOutSize)
static void ImGui_ImplWin32_UpdateMouseData()
{
ImGui_ImplWin32_Data* bd = ImGui_ImplWin32_GetBackendData();
ImGuiIO& io = ImGui::GetIO();
IM_ASSERT(bd->hWnd != 0);

POINT mouse_screen_pos;
bool has_mouse_screen_pos = ::GetCursorPos(&mouse_screen_pos) != 0;

// CET: Get and verify scale factor. If any scalar in the scale factor is <= 0, apply -FLT_MAX as mouse position event. Otherwise, process normally.
const auto scale = CET_GetScaleFactor();
if (scale.x <= 0.0f || scale.y <= 0.0f)
{
io.AddMousePosEvent(-FLT_MAX, -FLT_MAX);
return;
}

HWND focused_window = ::GetForegroundWindow();
const bool is_app_focused =
Expand All @@ -345,7 +368,7 @@ static void ImGui_ImplWin32_UpdateMouseData(SIZE aOutSize)
// When multi-viewports are enabled, all Dear ImGui positions are same as OS positions.
if (io.WantSetMousePos)
{
POINT pos = {(int)io.MousePos.x, (int)io.MousePos.y};
POINT pos = {static_cast<int>(io.MousePos.x / scale.x), static_cast<int>(io.MousePos.y / scale.y)};
if ((io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable) == 0)
::ClientToScreen(focused_window, &pos);
::SetCursorPos(pos.x, pos.y);
Expand All @@ -363,17 +386,7 @@ static void ImGui_ImplWin32_UpdateMouseData(SIZE aOutSize)
POINT mouse_pos = mouse_screen_pos;
if (!(io.ConfigFlags & ImGuiConfigFlags_ViewportsEnable))
::ScreenToClient(bd->hWnd, &mouse_pos);

static float xScale = 1.0;
static float yScale = 1.0;
if(aOutSize.cx && aOutSize.cy)
{
RECT clientRect;
::GetClientRect(bd->hWnd, &clientRect);
xScale = static_cast<float>(aOutSize.cx) / (clientRect.right - clientRect.left);
yScale = static_cast<float>(aOutSize.cy) / (clientRect.bottom - clientRect.top);
}
io.AddMousePosEvent((float)mouse_pos.x * xScale, (float)mouse_pos.y * yScale);
io.AddMousePosEvent((float)mouse_pos.x * scale.x, (float)mouse_pos.y * scale.y);
}
}

Expand Down Expand Up @@ -494,8 +507,7 @@ void ImGui_ImplWin32_NewFrame(SIZE aOutSize)
ImGuiIO& io = ImGui::GetIO();

// Setup display size (every frame to accommodate for window resizing)
// RECT rect = {0, 0, 0, 0};
// ::GetClientRect(bd->hWnd, &rect);
// CET: Use size provided by the game to match DLSS and similar.
io.DisplaySize = ImVec2(static_cast<float>(aOutSize.cx), static_cast<float>(aOutSize.cy));
if (bd->WantUpdateMonitors)
ImGui_ImplWin32_UpdateMonitors();
Expand All @@ -507,7 +519,7 @@ void ImGui_ImplWin32_NewFrame(SIZE aOutSize)
bd->Time = current_time;

// Update OS mouse position
ImGui_ImplWin32_UpdateMouseData(aOutSize);
ImGui_ImplWin32_UpdateMouseData();

// Process workarounds for known Windows key handling issues
ImGui_ImplWin32_ProcessKeyEventsWorkarounds();
Expand Down Expand Up @@ -702,6 +714,14 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARA
case WM_MOUSEMOVE:
case WM_NCMOUSEMOVE:
{
// CET: Get and verify scale factor. If any scalar in the scale factor is <= 0, apply -FLT_MAX as mouse position event. Otherwise, process normally.
const auto scale = CET_GetScaleFactor();
if (scale.x <= 0.0f || scale.y <= 0.0f)
{
io.AddMousePosEvent(-FLT_MAX, -FLT_MAX);
return 0;
}

// We need to call TrackMouseEvent in order to receive WM_MOUSELEAVE events
ImGuiMouseSource mouse_source = GetMouseSourceFromMessageExtraInfo();
const int area = (msg == WM_MOUSEMOVE) ? 1 : 2;
Expand All @@ -722,7 +742,7 @@ IMGUI_IMPL_API LRESULT ImGui_ImplWin32_WndProcHandler(HWND hwnd, UINT msg, WPARA
if (msg == WM_NCMOUSEMOVE && !want_absolute_pos) // WM_NCMOUSEMOVE are absolute coordinates.
::ScreenToClient(hwnd, &mouse_pos);
io.AddMouseSourceEvent(mouse_source);
io.AddMousePosEvent((float)mouse_pos.x, (float)mouse_pos.y);
io.AddMousePosEvent((float)mouse_pos.x * scale.x, (float)mouse_pos.y * scale.y);
return 0;
}
case WM_MOUSELEAVE:
Expand Down