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…DL_CreateWindowFrom() to set the pixel format of another SDL_Window (and also will set the SDL_WINDOW_OPENGL flag on the window created with SDL_CreateWindowFrom()).

The reasoning behind this change is that source2 in -tools mode has a single OpenGL context that is used with multiple different windows.  Some of those windows are created outside the engine (i.e. with Qt) and therefore we need to use SDL_CreateWindowFrom() to get an SDL_Window for those.  The requirement for sharing an OpenGL context across multiple different windows is that each window has the same pixel format.  To facilitate this, I now set SDL_HINT_VIDEO_WINDOW_SHARE_PIXEL_FORMAT for the main window before calling SDL_CreateWindowFrom().  When I do this, SDL_CreateWindowFrom() will:

1. Set the pixel format of the returned window to the same pixel format as this SDL_Window passed in with the hint
2. The flag SDL_WINDOW_OPENGL will be set on the new window so it can be used for OpenGL rendering.

I only currently implemented this for Win32/WGL so implementing it for other platforms (i.e. X11) remains a TODO.

CR: SamL

Some pseudocode that shows how this is used in Source2:

HWND hExternalHwnd; // HWND that was established outside of SDL

// Create main window (happens inside platwindow.cpp)
SDL_Window *mainWindow = SDL_CreateWindow( , SDL_WINDOW_OPENGL .. );
// Create GL context, happens inside rendersystemgl
SDL_GLContext onlyContext = SDL_GL_CreateContext( mainWindow );

// Now I need to create another window from hEternalHwnd for my swap chain that will have the same pixel format as mainWindow, so set the hint

// Create the secondary window.  This returned window will have SDL_WINDOW_OPENGL set and share a pixel format with mainWindow from the hint
SDL_Window *secondaryWindow = SDL_CreateWindowFrom( hExternalHwnd );

// To render to the main window:
SDL_GL_MakeCurrent( mainWindow, onlyContext );
// Do some rendering to main window

// To render to the secondary window:
SDL_GLMakeCurrent( secondaryWindow, onlyContext );
// Do some rendering to secondary window
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slouken committed Jan 30, 2014
1 parent dbd4a91 commit d76c2cc
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19 changes: 19 additions & 0 deletions include/SDL_hints.h
Expand Up @@ -328,6 +328,25 @@ extern "C" {

* \brief A variable that is the address of another SDL_Window* (as a hex string formatted with "%p").
* If this hint is set before SDL_CreateWindowFrom() and the SDL_Window* it is set to has
* SDL_WINDOW_OPENGL set (and running on WGL only, currently), then two things will occur on the newly
* created SDL_Window:
* 1. Its pixel format will be set to the same pixel format as this SDL_Window. This is
* needed for example when sharing an OpenGL context across multiple windows.
* 2. The flag SDL_WINDOW_OPENGL will be set on the new window so it can be used for
* OpenGL rendering.
* This variable can be set to the following values:
* The address (as a string "%p") of the SDL_Window* that new windows created with SDL_CreateWindowFrom() should
* share a pixel format with.

* \brief An enumeration of hint priorities
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20 changes: 20 additions & 0 deletions src/video/windows/SDL_windowsopengl.c
Expand Up @@ -759,6 +759,26 @@ WIN_GL_DeleteContext(_THIS, SDL_GLContext context)
_this->gl_data->wglDeleteContext((HGLRC) context);

WIN_GL_SetPixelFormatFrom(_THIS, SDL_Window * fromWindow, SDL_Window * toWindow)
HDC hfromdc = ((SDL_WindowData *) fromWindow->driverdata)->hdc;
HDC htodc = ((SDL_WindowData *) toWindow->driverdata)->hdc;
BOOL result;

/* get the pixel format of the fromWindow */
int pixel_format = GetPixelFormat(hfromdc);
SDL_memset(&pfd, 0, sizeof(pfd));
DescribePixelFormat(hfromdc, pixel_format, sizeof(pfd), &pfd);

/* set the pixel format of the toWindow */
result = SetPixelFormat(htodc, pixel_format, &pfd);

return result ? SDL_TRUE : SDL_FALSE;


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1 change: 1 addition & 0 deletions src/video/windows/SDL_windowsopengl.h
Expand Up @@ -64,6 +64,7 @@ extern int WIN_GL_GetSwapInterval(_THIS);
extern void WIN_GL_SwapWindow(_THIS, SDL_Window * window);
extern void WIN_GL_DeleteContext(_THIS, SDL_GLContext context);
extern void WIN_GL_InitExtensions(_THIS);
extern SDL_bool WIN_GL_SetPixelFormatFrom(_THIS, SDL_Window * fromWindow, SDL_Window * toWindow);

#ifndef WGL_ARB_pixel_format
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26 changes: 26 additions & 0 deletions src/video/windows/SDL_windowswindow.c
Expand Up @@ -32,6 +32,7 @@

#include "SDL_windowsvideo.h"
#include "SDL_windowswindow.h"
#include "SDL_hints.h"

/* Dropfile support */
#include <shellapi.h>
Expand Down Expand Up @@ -337,6 +338,31 @@ WIN_CreateWindowFrom(_THIS, SDL_Window * window, const void *data)
if (SetupWindowData(_this, window, hwnd, SDL_FALSE) < 0) {
return -1;

if (hint) {
// This hint is a pointer (in string form) of the address of
// the window to share a pixel format with
SDL_Window *otherWindow = NULL;
SDL_sscanf(hint, "%p", (void**)&otherWindow);

// Do some error checking on the pointer
if (otherWindow != NULL && otherWindow->magic == &_this->window_magic)
// If the otherWindow has SDL_WINDOW_OPENGL set, set it for the new window as well
if (otherWindow->flags & SDL_WINDOW_OPENGL)
window->flags |= SDL_WINDOW_OPENGL;
if(!WIN_GL_SetPixelFormatFrom(_this, otherWindow, window)) {
return -1;
return 0;

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