Implemented bug #2, 117:

Date: Mon, 21 Mar 2005 12:06:14 +0100
From: Per Inge Mathisen
Subject: Re: [SDL] Outstanding patches?

The patch adds support for setting SDL_GL_SWAP_CONTROL to Windows and
X11. In Windows you can also query this enum to check that it is
working, or see what the default is - such functionality does not
exist in GLX. For more information on the standards implemented:
http://oss.sgi.com/projects/ogl-sample/registry/SGI/swap_control.txt
http://oss.sgi.com/projects/ogl-sample/registry/EXT/wgl_swap_control.txt

--HG--
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/trunk%401671

WhatsNew

@@ -4,6 +4,8 @@ This is a list of API changes in SDL's version history.
 Version 1.0:
 
 1.2.10:
+	Added SDL_GL_SWAP_CONTROL to wait for vsync in OpenGL applications.
+
 	Added current_w and current_h to the SDL_VideoInfo structure,
 	which is set to the desktop resolution during video intialization,
 	and then set to the current resolution when a video mode is set.

include/SDL_video.h

@@ -213,7 +213,8 @@ typedef enum {
     SDL_GL_ACCUM_ALPHA_SIZE,
     SDL_GL_STEREO,
     SDL_GL_MULTISAMPLEBUFFERS,
-    SDL_GL_MULTISAMPLESAMPLES
+    SDL_GL_MULTISAMPLESAMPLES,
+    SDL_GL_SWAP_CONTROL
 } SDL_GLattr;
 
 /* flags for SDL_SetPalette() */

src/video/SDL_sysvideo.h

@@ -292,6 +292,7 @@ struct SDL_VideoDevice {
 		int stereo;
 		int multisamplebuffers;
 		int multisamplesamples;
+		int swap_control;
 		int driver_loaded;
 		char driver_path[256];
 		void* dll_handle;

src/video/SDL_video.c

@@ -233,6 +233,7 @@ int SDL_VideoInit (const char *driver_name, Uint32 flags)
 	video->gl_config.stereo = 0;
 	video->gl_config.multisamplebuffers = 0;
 	video->gl_config.multisamplesamples = 0;
+	video->gl_config.swap_control = -1; /* not known, don't set */
 	
 	/* Initialize the video subsystem */
 	SDL_memset(&vformat, 0, sizeof(vformat));
@@ -1474,6 +1475,9 @@ int SDL_GL_SetAttribute( SDL_GLattr attr, int value )
 		case SDL_GL_MULTISAMPLESAMPLES:
 			video->gl_config.multisamplesamples = value;
 			break;
+		case SDL_GL_SWAP_CONTROL:
+			video->gl_config.swap_control = value;
+			break;
 		default:
 			SDL_SetError("Unknown OpenGL attribute");
 			retval = -1;

src/video/quartz/SDL_QuartzGL.m

@@ -132,6 +132,17 @@ int QZ_SetupOpenGL (_THIS, int bpp, Uint32 flags) {
         return 0;
     }
 
+    /* Synchronize QZ_GL_SwapBuffers() to vertical retrace.
+     * (Apple's documentation is not completely clear about what this setting
+     * exactly does, IMHO - for a detailed explanation see
+     * http://lists.apple.com/archives/mac-opengl/2006/Jan/msg00080.html )
+     */
+    if ( this->gl_config.swap_control >= 0 ) {
+        long value;
+        value = this->gl_config.swap_control;
+        [ gl_context setValues: &value forParameter: NSOpenGLCPSwapInterval ];
+    }
+
     /*
      * Wisdom from Apple engineer in reference to UT2003's OpenGL performance:
      *  "You are blowing a couple of the internal OpenGL function caches. This

src/video/wincommon/SDL_wingl.c

@@ -177,6 +177,7 @@ int WIN_GL_SetupWindow(_THIS)
 	int iAttribs[64];
 	int *iAttr;
 	float fAttribs[1] = { 0 };
+	const char *wglext;
 
 	/* load the gl driver from a default path */
 	if ( ! this->gl_config.driver_loaded ) {
@@ -323,7 +324,25 @@ int WIN_GL_SetupWindow(_THIS)
 		SDL_SetError("Unable to create GL context");
 		return(-1);
 	}
+	if ( WIN_GL_MakeCurrent(this) < 0 ) {
+		return(-1);
+	}
 	gl_active = 1;
+
+	/* Vsync control under Windows.  Checking glGetString here is
+	 * somewhat a documented and reliable hack - it was originally
+	 * as a feature added by mistake, but since so many people rely
+	 * on it, it will not be removed.  strstr should be safe here.*/
+	wglext = (const char *)this->glGetString(GL_EXTENSIONS);
+	if ( !SDL_strstr(wglext, "WGL_EXT_swap_control") ) {
+		this->gl_data->wglSwapIntervalEXT = NULL;
+		this->gl_data->wglGetSwapIntervalEXT = NULL;
+	}
+	if ( this->gl_config.swap_control >= 0 ) {
+		if ( this->gl_data->wglSwapIntervalEXT ) {
+			this->gl_data->wglSwapIntervalEXT(this->gl_config.swap_control);
+		}
+	}
 #else
 	SDL_SetError("WIN driver not configured with OpenGL");
 #endif
@@ -423,6 +442,12 @@ int WIN_GL_GetAttribute(_THIS, SDL_GLattr attrib, int* value)
 		    case SDL_GL_MULTISAMPLESAMPLES:
 			wgl_attrib = WGL_SAMPLES_ARB;
 			break;
+		    case SDL_GL_SWAP_CONTROL:
+			if ( this->gl_data->wglGetSwapIntervalEXT ) {
+				return this->gl_data->wglGetSwapIntervalEXT();
+			} else {
+				return -1;
+			}
 		    default:
 			return(-1);
 		}
@@ -509,6 +534,8 @@ void WIN_GL_UnloadLibrary(_THIS)
 		this->gl_data->wglMakeCurrent = NULL;
 		this->gl_data->wglChoosePixelFormatARB = NULL;
 		this->gl_data->wglGetPixelFormatAttribivARB = NULL;
+		this->gl_data->wglSwapIntervalEXT = NULL;
+		this->gl_data->wglGetSwapIntervalEXT = NULL;
 
 		this->gl_config.dll_handle = NULL;
 		this->gl_config.driver_loaded = 0;
@@ -547,6 +574,10 @@ int WIN_GL_LoadLibrary(_THIS, const char* path)
 		GetProcAddress(handle, "wglDeleteContext");
 	this->gl_data->wglMakeCurrent = (BOOL (WINAPI *)(HDC, HGLRC))
 		GetProcAddress(handle, "wglMakeCurrent");
+	this->gl_data->wglSwapIntervalEXT = (void (WINAPI *)(int))
+		GetProcAddress(handle, "wglSwapIntervalEXT");
+	this->gl_data->wglGetSwapIntervalEXT = (int (WINAPI *)(void))
+		GetProcAddress(handle, "wglGetSwapIntervalEXT");
 
 	if ( (this->gl_data->wglGetProcAddress == NULL) ||
 	     (this->gl_data->wglCreateContext == NULL) ||

src/video/wincommon/SDL_wingl_c.h

@@ -53,6 +53,8 @@ struct SDL_PrivateGLData {
                                                 UINT nAttributes, 
                                                 const int *piAttributes,
                                                 int *piValues);
+    void (WINAPI *wglSwapIntervalEXT)(int interval);
+    int (WINAPI *wglGetSwapIntervalEXT)(void);
 #endif /* SDL_VIDEO_OPENGL */
 };
 

src/video/x11/SDL_x11gl.c

@@ -205,6 +205,8 @@ int X11_GL_CreateContext(_THIS)
 {
 	int retval;
 #if SDL_VIDEO_OPENGL_GLX
+	const char *glXext;
+
 	/* We do this to create a clean separation between X and GLX errors. */
 	XSync( SDL_Display, False );
 	glx_context = this->gl_data->glXCreateContext(GFX_Display, 
@@ -213,10 +215,29 @@ int X11_GL_CreateContext(_THIS)
 
 	if ( glx_context == NULL ) {
 		SDL_SetError("Could not create GL context");
-		return -1;
+		return(-1);
+	}
+	if ( X11_GL_MakeCurrent(this) < 0 ) {
+		return(-1);
 	}
-
 	gl_active = 1;
+
+	/* The use of strstr here should be safe */
+	glXext = this->gl_data->glXQueryExtensionsString(GFX_Display, DefaultScreen(GFX_Display));
+	if ( !SDL_strstr(glXext, "SGI_swap_control") ) {
+		this->gl_data->glXSwapIntervalSGI = NULL;
+	}
+	if ( !SDL_strstr(glXext, "GLX_MESA_swap_control") ) {
+		this->gl_data->glXSwapIntervalMESA = NULL;
+		this->gl_data->glXGetSwapIntervalMESA = NULL;
+	}
+	if ( this->gl_config.swap_control >= 0 ) {
+		if ( this->gl_data->glXSwapIntervalMESA ) {
+			this->gl_data->glXSwapIntervalMESA(this->gl_config.swap_control);
+		} else if ( this->gl_data->glXSwapIntervalSGI ) {
+			this->gl_data->glXSwapIntervalSGI(this->gl_config.swap_control);
+		}
+	}
 #else
 	SDL_SetError("X11 driver not configured with OpenGL");
 #endif
@@ -319,6 +340,13 @@ int X11_GL_GetAttribute(_THIS, SDL_GLattr attrib, int* value)
  	    case SDL_GL_MULTISAMPLESAMPLES:
  		glx_attrib = GLX_SAMPLES_ARB;
  		break;
+	    case SDL_GL_SWAP_CONTROL:
+		if ( this->gl_data->glXGetSwapIntervalMESA ) {
+			return this->gl_data->glXGetSwapIntervalMESA();
+		} else {
+			return -1 /*(this->gl_config.swap_control > 0)*/;
+		}
+		break;
 	    default:
 		return(-1);
 	}
@@ -348,6 +376,9 @@ void X11_GL_UnloadLibrary(_THIS)
 		this->gl_data->glXDestroyContext = NULL;
 		this->gl_data->glXMakeCurrent = NULL;
 		this->gl_data->glXSwapBuffers = NULL;
+		this->gl_data->glXSwapIntervalSGI = NULL;
+		this->gl_data->glXSwapIntervalMESA = NULL;
+		this->gl_data->glXGetSwapIntervalMESA = NULL;
 
 		this->gl_config.dll_handle = NULL;
 		this->gl_config.driver_loaded = 0;
@@ -400,7 +431,12 @@ int X11_GL_LoadLibrary(_THIS, const char* path)
 		(int (*)(Display *, XVisualInfo *, int, int *)) SDL_LoadFunction(handle, "glXGetConfig");
 	this->gl_data->glXQueryExtensionsString =
 		(const char *(*)(Display *, int)) SDL_LoadFunction(handle, "glXQueryExtensionsString");
-	
+	this->gl_data->glXSwapIntervalSGI =
+		(int (*)(int)) SDL_LoadFunction(handle, "glXSwapIntervalSGI");
+	this->gl_data->glXSwapIntervalMESA =
+		(GLint (*)(unsigned)) SDL_LoadFunction(handle, "glXSwapIntervalMESA");
+	this->gl_data->glXGetSwapIntervalMESA =
+		(GLint (*)(void)) SDL_LoadFunction(handle, "glXGetSwapIntervalMESA");
 
 	if ( (this->gl_data->glXChooseVisual == NULL) || 
 	     (this->gl_data->glXCreateContext == NULL) ||

src/video/x11/SDL_x11gl_c.h

@@ -71,6 +71,9 @@ struct SDL_PrivateGLData {
 	    ( Display* dpy,
 	      int screen );
 
+    int (*glXSwapIntervalSGI) ( int interval );
+    GLint (*glXSwapIntervalMESA) ( unsigned interval );
+    GLint (*glXGetSwapIntervalMESA) ( void );
 
 #endif /* SDL_VIDEO_OPENGL_GLX */
 };

test/testgl.c

@@ -445,7 +445,7 @@ void DrawLogoBlit(void)
 }
 
 int RunGLTest( int argc, char* argv[],
-               int logo, int logocursor, int slowly, int bpp, float gamma, int noframe, int fsaa )
+               int logo, int logocursor, int slowly, int bpp, float gamma, int noframe, int fsaa, int sync )
 {
 	int i;
 	int rgb_size[3];
@@ -531,6 +531,11 @@ int RunGLTest( int argc, char* argv[],
 		SDL_GL_SetAttribute( SDL_GL_MULTISAMPLEBUFFERS, 1 );
 		SDL_GL_SetAttribute( SDL_GL_MULTISAMPLESAMPLES, fsaa );
 	}
+	if ( sync ) {
+		SDL_GL_SetAttribute( SDL_GL_SWAP_CONTROL, 1 );
+	} else {
+		SDL_GL_SetAttribute( SDL_GL_SWAP_CONTROL, 0 );
+	}
 	if ( SDL_SetVideoMode( w, h, bpp, video_flags ) == NULL ) {
 		fprintf(stderr, "Couldn't set GL mode: %s\n", SDL_GetError());
 		SDL_Quit();
@@ -561,6 +566,10 @@ int RunGLTest( int argc, char* argv[],
 		SDL_GL_GetAttribute( SDL_GL_MULTISAMPLESAMPLES, &value );
 		printf("SDL_GL_MULTISAMPLESAMPLES: requested %d, got %d\n", fsaa, value );
 	}
+	if ( sync ) {
+		SDL_GL_GetAttribute( SDL_GL_SWAP_CONTROL, &value );
+		printf( "SDL_GL_SWAP_CONTROL: requested 1, got %d\n", value );
+	}
 
 	/* Set the window manager title bar */
 	SDL_WM_SetCaption( "SDL GL test", "testgl" );
@@ -770,6 +779,7 @@ int main(int argc, char *argv[])
 	float gamma = 0.0;
 	int noframe = 0;
 	int fsaa = 0;
+	int sync = 0;
 
 	logo = 0;
 	slowly = 0;
@@ -804,6 +814,9 @@ int main(int argc, char *argv[])
 		if ( strcmp(argv[i], "-fsaa") == 0 ) {
  		       ++fsaa;
 		}
+		if ( strcmp(argv[i], "-sync") == 0 ) {
+ 		       ++sync;
+		}
 		if ( strncmp(argv[i], "-h", 2) == 0 ) {
  		       printf(
 "Usage: %s [-twice] [-logo] [-logocursor] [-slow] [-bpp n] [-gamma n] [-noframe] [-fsaa] [-fullscreen]\n",
@@ -812,7 +825,7 @@ int main(int argc, char *argv[])
 		}
 	}
 	for ( i=0; i<numtests; ++i ) {
- 		RunGLTest(argc, argv, logo, logocursor, slowly, bpp, gamma, noframe, fsaa);
+ 		RunGLTest(argc, argv, logo, logocursor, slowly, bpp, gamma, noframe, fsaa, sync);
 	}
 	return 0;
 }