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Refined fix for issue ocornut#2600
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ImGui_ImplWin32_Init() now optionally accepts a render context handle,
and IMGUI_IMPL_WIN32_OPENGL3 is no longer a necessary define.
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@theOtherMichael
theOtherMichael committed Apr 6, 2022
1 parent 4955f4b commit 31aedf7
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Showing 2 changed files with 72 additions and 63 deletions.
129 changes: 71 additions & 58 deletions backends/imgui_impl_win32.cpp
View file
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,14 @@
#include <tchar.h>
#include <dwmapi.h>

// Stuff for loading WGL functions explicitly
#include <cstdlib> // atexit()
static HMODULE libgl;
HGLRC (WINAPI* _wglCreateContext)(HDC);
BOOL (WINAPI* _wglDeleteContext)(HGLRC);
BOOL (WINAPI* _wglMakeCurrent)(HDC, HGLRC);
BOOL (WINAPI* _wglShareLists)(HGLRC, HGLRC);

// Configuration flags to add in your imconfig.h file:
//#define IMGUI_IMPL_WIN32_DISABLE_GAMEPAD // Disable gamepad support. This was meaningful before <1.81 but we now load XInput dynamically so the option is now less relevant.

Expand Down Expand Up @@ -88,6 +96,8 @@ static void ImGui_ImplWin32_ShowWindow(ImGuiViewport* viewport);
struct ImGui_ImplWin32_Data
{
HWND hWnd;
HDC Hdc;
HGLRC HgLrc;
HWND MouseHwnd;
bool MouseTracked;
int MouseButtonsDown;
Expand All @@ -98,10 +108,6 @@ struct ImGui_ImplWin32_Data
bool WantUpdateHasGamepad;
bool WantUpdateMonitors;

#ifdef IMGUI_IMPL_WIN32_OPENGL3
HGLRC HgLrc;
#endif //IMGUI_IMPL_WIN32_OPENGL3

#ifndef IMGUI_IMPL_WIN32_DISABLE_GAMEPAD
HMODULE XInputDLL;
PFN_XInputGetCapabilities XInputGetCapabilities;
Expand All @@ -121,11 +127,7 @@ static ImGui_ImplWin32_Data* ImGui_ImplWin32_GetBackendData()
}

// Functions
#ifdef IMGUI_IMPL_WIN32_OPENGL3
bool ImGui_ImplWin32_Init(void* hwnd, void* hglrc)
#else
bool ImGui_ImplWin32_Init(void* hwnd)
#endif
{
ImGuiIO& io = ImGui::GetIO();
IM_ASSERT(io.BackendPlatformUserData == NULL && "Already initialized a platform backend!");
Expand All @@ -136,6 +138,25 @@ bool ImGui_ImplWin32_Init(void* hwnd)
if (!::QueryPerformanceCounter((LARGE_INTEGER*)&perf_counter))
return false;

// Load WGL symbols explicitly
// This is needed to allow compilation if and when non-OpenGL APIs are used with Win32.
// The function pointer names are preceded with an underscore ("_") to prevent duplicate
// symbols in projects where OpenGL32.dll is linked implicitly.
if (hglrc)
{
libgl = LoadLibraryA("opengl32.dll");
IM_ASSERT(libgl);
_wglCreateContext = (HGLRC(WINAPI*)(HDC))GetProcAddress(libgl, "wglCreateContext");
_wglDeleteContext = (BOOL(WINAPI*)(HGLRC))GetProcAddress(libgl, "wglDeleteContext");
_wglMakeCurrent = (BOOL(WINAPI*)(HDC, HGLRC))GetProcAddress(libgl, "wglMakeCurrent");
_wglShareLists = (BOOL(WINAPI*)(HGLRC, HGLRC))GetProcAddress(libgl, "wglShareLists");
IM_ASSERT(_wglCreateContext);
IM_ASSERT(_wglDeleteContext);
IM_ASSERT(_wglMakeCurrent);
IM_ASSERT(_wglShareLists);
atexit([](){ FreeLibrary(libgl); });
}

// Setup backend capabilities flags
ImGui_ImplWin32_Data* bd = IM_NEW(ImGui_ImplWin32_Data)();
io.BackendPlatformUserData = (void*)bd;
Expand All @@ -146,16 +167,14 @@ bool ImGui_ImplWin32_Init(void* hwnd)
io.BackendFlags |= ImGuiBackendFlags_HasMouseHoveredViewport; // We can call io.AddMouseViewportEvent() with correct data (optional)

bd->hWnd = (HWND)hwnd;
bd->Hdc = GetDC(bd->hWnd);
bd->HgLrc = (HGLRC)hglrc; // OpenGL
bd->WantUpdateHasGamepad = true;
bd->WantUpdateMonitors = true;
bd->TicksPerSecond = perf_frequency;
bd->Time = perf_counter;
bd->LastMouseCursor = ImGuiMouseCursor_COUNT;

#ifdef IMGUI_IMPL_WIN32_OPENGL3
bd->HgLrc = (HGLRC)hglrc;
#endif //IMGUI_IMPL_WIN32_OPENGL3

// Our mouse update function expect PlatformHandle to be filled for the main viewport
ImGuiViewport* main_viewport = ImGui::GetMainViewport();
main_viewport->PlatformHandle = main_viewport->PlatformHandleRaw = (void*)bd->hWnd;
Expand Down Expand Up @@ -857,25 +876,19 @@ struct ImGui_ImplWin32_ViewportData
{
HWND Hwnd;
bool HwndOwned;
DWORD DwStyle;
DWORD DwExStyle;

#ifdef IMGUI_IMPL_WIN32_OPENGL3
HDC Hdc;
HGLRC HgLrc;
#endif //IMGUI_IMPL_WIN32_OPENGL3
DWORD DwStyle;
DWORD DwExStyle;

ImGui_ImplWin32_ViewportData()
{
Hwnd = NULL;
HwndOwned = false;
DwStyle = 0;
DwExStyle = 0;

#ifdef IMGUI_IMPL_WIN32_OPENGL3
Hdc = NULL;
HgLrc = NULL;
#endif //IMGUI_IMPL_WIN32_OPENGL3
DwStyle = 0;
DwExStyle = 0;
}
~ImGui_ImplWin32_ViewportData() { IM_ASSERT(Hwnd == NULL); }
};
Expand Down Expand Up @@ -916,29 +929,28 @@ static void ImGui_ImplWin32_CreateWindow(ImGuiViewport* viewport)
rect.left, rect.top, rect.right - rect.left, rect.bottom - rect.top, // Window area
parent_window, NULL, ::GetModuleHandle(NULL), NULL); // Parent window, Menu, Instance, Param
vd->HwndOwned = true;
vd->Hdc = GetDC(vd->Hwnd);
viewport->PlatformRequestResize = false;
viewport->PlatformHandle = viewport->PlatformHandleRaw = vd->Hwnd;

#ifdef IMGUI_IMPL_WIN32_OPENGL3
vd->Hdc = GetDC(vd->Hwnd);
ImGui_ImplWin32_Data* bd = ImGui_ImplWin32_GetBackendData();

// Set pixel format to match base window
HDC Hdc = GetDC(bd->hWnd);
int pf = GetPixelFormat(Hdc);
PIXELFORMATDESCRIPTOR pfd;
DescribePixelFormat(Hdc, pf, sizeof(pfd), &pfd);
SetPixelFormat(vd->Hdc, pf, &pfd);

// Create OpenGL context for new window
vd->HgLrc = wglCreateContext(vd->Hdc);
wglMakeCurrent(vd->Hdc, vd->HgLrc);
wglShareLists(bd->HgLrc, vd->HgLrc);

// Present new window
ImGui_ImplWin32_SetWindowFocus(viewport);
ImGui_ImplWin32_ShowWindow(viewport);
#endif //IMGUI_IMPL_WIN32_OPENGL3
if (bd->HgLrc) // OpenGL
{
// Use the main window's pixel format
int pf = GetPixelFormat(bd->Hdc);
PIXELFORMATDESCRIPTOR pfd;
DescribePixelFormat(bd->Hdc, pf, sizeof(pfd), &pfd);
SetPixelFormat(vd->Hdc, pf, &pfd);

// Create OpenGL context and share main context's lists with it
vd->HgLrc = _wglCreateContext(vd->Hdc);
_wglMakeCurrent(vd->Hdc, vd->HgLrc);
_wglShareLists(bd->HgLrc, vd->HgLrc);

// Present window
ImGui_ImplWin32_SetWindowFocus(viewport);
ImGui_ImplWin32_ShowWindow(viewport);
}
}

static void ImGui_ImplWin32_DestroyWindow(ImGuiViewport* viewport)
Expand All @@ -954,9 +966,8 @@ static void ImGui_ImplWin32_DestroyWindow(ImGuiViewport* viewport)
}
if (vd->Hwnd && vd->HwndOwned)
{
#ifdef IMGUI_IMPL_WIN32_OPENGL3
wglDeleteContext(vd->HgLrc);
#endif //IMGUI_IMPL_WIN32_OPENGL3
if (vd->HgLrc)
_wglDeleteContext(vd->HgLrc);

::DestroyWindow(vd->Hwnd);
}
Expand Down Expand Up @@ -1119,20 +1130,20 @@ static void ImGui_ImplWin32_OnChangedViewport(ImGuiViewport* viewport)
#endif
}

#ifdef IMGUI_IMPL_WIN32_OPENGL3
static void ImGui_ImplWin32_RenderWindow(ImGuiViewport* viewport, void*)
static void ImGui_ImplWin32_OGL_RenderWindow(ImGuiViewport* viewport, void*)
{
ImGui_ImplWin32_ViewportData* vd = (ImGui_ImplWin32_ViewportData*)viewport->PlatformUserData;
wglMakeCurrent(vd->Hdc, vd->HgLrc);
IM_ASSERT(vd->HgLrc); // ImGui_ImplWin32_OGL_RenderWindow() is only registered if API is OpenGL
_wglMakeCurrent(vd->Hdc, vd->HgLrc);
}

static void ImGui_ImplWin32_SwapBuffers(ImGuiViewport* viewport, void*)
static void ImGui_ImplWin32_OGL_SwapBuffers(ImGuiViewport* viewport, void*)
{
ImGui_ImplWin32_ViewportData* vd = (ImGui_ImplWin32_ViewportData*)viewport->PlatformUserData;
wglMakeCurrent(vd->Hdc, vd->HgLrc);
IM_ASSERT(vd->HgLrc); // ImGui_ImplWin32_OGL_SwapBuffers() is only registered if API is OpenGL
_wglMakeCurrent(vd->Hdc, vd->HgLrc);
SwapBuffers(vd->Hdc);
}
#endif //IMGUI_IMPL_WIN32_OPENGL3

static LRESULT CALLBACK ImGui_ImplWin32_WndProcHandler_PlatformWindow(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
Expand All @@ -1143,10 +1154,9 @@ static LRESULT CALLBACK ImGui_ImplWin32_WndProcHandler_PlatformWindow(HWND hWnd,
{
switch (msg)
{
#ifdef IMGUI_IMPL_WIN32_OPENGL3
case WM_ERASEBKGND:
return 0; // Prevent flickering on window invalidation
#endif //IMGUI_IMPL_WIN32_OPENGL3
// Prevent flickering on window invalidation
return TRUE;
case WM_CLOSE:
viewport->PlatformRequestClose = true;
return 0;
Expand Down Expand Up @@ -1211,18 +1221,21 @@ static void ImGui_ImplWin32_InitPlatformInterface()
platform_io.Platform_GetWindowDpiScale = ImGui_ImplWin32_GetWindowDpiScale; // FIXME-DPI
platform_io.Platform_OnChangedViewport = ImGui_ImplWin32_OnChangedViewport; // FIXME-DPI

#ifdef IMGUI_IMPL_WIN32_OPENGL3
platform_io.Platform_RenderWindow = ImGui_ImplWin32_RenderWindow;
platform_io.Platform_SwapBuffers = ImGui_ImplWin32_SwapBuffers;
#endif //IMGUI_IMPL_WIN32_OPENGL3
ImGui_ImplWin32_Data* bd = ImGui_ImplWin32_GetBackendData();
if (bd->HgLrc) // OpenGL
{
platform_io.Platform_RenderWindow = ImGui_ImplWin32_OGL_RenderWindow;
platform_io.Platform_SwapBuffers = ImGui_ImplWin32_OGL_SwapBuffers;
}

// Register main window handle (which is owned by the main application, not by us)
// This is mostly for simplicity and consistency, so that our code (e.g. mouse handling etc.) can use same logic for main and secondary viewports.
ImGuiViewport* main_viewport = ImGui::GetMainViewport();
ImGui_ImplWin32_Data* bd = ImGui_ImplWin32_GetBackendData();
ImGui_ImplWin32_ViewportData* vd = IM_NEW(ImGui_ImplWin32_ViewportData)();
vd->Hwnd = bd->hWnd;
vd->HwndOwned = false;
vd->Hdc = bd->Hdc;
vd->HgLrc = bd->HgLrc; // OpenGL
main_viewport->PlatformUserData = vd;
main_viewport->PlatformHandle = (void*)bd->hWnd;
}
Expand Down
6 changes: 1 addition & 5 deletions backends/imgui_impl_win32.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -16,11 +16,7 @@
#pragma once
#include "imgui.h" // IMGUI_IMPL_API

#ifdef IMGUI_IMPL_WIN32_OPENGL3
IMGUI_IMPL_API bool ImGui_ImplWin32_Init(void* hwnd, void* hglrc);
#else
IMGUI_IMPL_API bool ImGui_ImplWin32_Init(void* hwnd);
#endif
IMGUI_IMPL_API bool ImGui_ImplWin32_Init(void* hwnd, void* hglrc = NULL);
IMGUI_IMPL_API void ImGui_ImplWin32_Shutdown();
IMGUI_IMPL_API void ImGui_ImplWin32_NewFrame();

Expand Down

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