#Introduction Most tutorials seem to start off with a discussion of how hard X is, how it will mess up your head and how only a masochist would ever write X code with alternates such as SDL out there. This, in my opinion is just wrong. In the trinity of major operating systems i think X is the sanest, most reliable and cleanest designed window manager. With that in mind, lets create an OpenGL enabled X11 window for video games.
#Part 1, Creating a Window The X windowing system uses a client/server architecture. A single machine can have X running in multiple instances.
##Creating an X Window The first thing to do when opening a window under x is to tell it where the screen is. Altough there are several ways of telling the client where the server is, the most fullproof is the DISPLAY environment variable, or using NULL for default.
The function XOpenDisplay(char* display) makes the connection to the X server. It takes one argument, a string using the display format described above, or NULL to use the default. It returns a pointer to the display (of type Display) on success or NULL on error.
With the pointer the display, find the screen using the DefaultScreenOfDisplay(Display* display) function. This function takes one parameter, the pointer to the Display object that was found using XOpenDisplay. DefaultScreenOfDisplay returns a pointer of type Screen on success, NULL on error.
To find the screen ID of the screen use the DefaultScreen(Display* display) function, this is almost identical to DefaultScreenOfDisplay except that it retuns an integer.
With just a display and a screen a window can be created with the XCreateSimpleWindow function. The prototype for this function is as follows
Window XCreateSimpleWindow(Display* display, Window* parent, int x, int y, uint borderw, ulong border, ulong background);
The first argument display is a pointer to the display object acquired using XOpenDisplay. The next argument, parent is a pointer to the window opening this one. If this is the first window of a program opening, use the RootWindowOfScreen(Screen* screen) function. This function takes one argument, the pointer to the screen that was acquired using DefaultScreenOfDisplay
The next four arguments are the location and sizeof the window. the border-width argument specifies the width of the window border in pixels. The next argument border is the color of the border. The last paramater background is simply the background color of the window.
There are several utility functions to acquire system colors (of type ulong). BlackPixel(Display* display, int screenId) and WhitePixel(Display* display, int screenId) are great examples. All of these functions take two arguments, a pointer to the display to use and the screenId being used.
The next step is to clear the window using XClearWindow(Display* display, Window* window), this function takes two arguments the display and the window to clear. Finally raise the window using the XMapRaised(Display* display, Window* window) function, which uses the same arguments as XClearWindow
At this point the window will not show up yet. First it must process messages (such as show window) that are sent to it. To process messages, start a "message loop", in it call XNextEvent(Display* display, XEvent* e). This function will return the current active event, or block until the next event is recieved. It take a Display object as it's first argument and writes to an XEvent pointer that is it's second argument.
After the window is finished, force the window to close with the XDestroyWindow(Display* display, Window window) function and cleanup the display using the XCloseDisplay(Display* display) function, which takes one argument, the display to close.
###Sample Code (C)
#include <X11/Xlib.h>
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
printf("%s\n", "Could not open display");
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Open the window
window = XCreateSimpleWindow(display, RootWindowOfScreen(screen), 0, 0, 320, 200, 1, BlackPixel(display, screenId), WhitePixel(display, screenId));
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
// Enter message loop
while (true) {
XNextEvent(display, &ev);
// Do something
}
// Cleanup
XDestroyWindow(display, window);
XFree(screen);
XCloseDisplay(display);
return 1;
}
Compile the program using the following command line
LINUX: gcc -o XSampleWindow XSampleWindow.c -lX11 -L/usr/X11R6/lib -I/usr/X11R6/include
OSX: gcc -o XSampleWindow XSampleWindow.c -lX11 -L/usr/X11/lib -I/opt/X11/include
#Part 2, Processing Events
To register for events use the XSelectInput(Display* display, uint mask) function, it takes as arguments the display object, the window object and a bitmask representing what events the message loop will subscribe to. This function should be called before the XMapWindow function.
TODO: Event table listing http://tronche.com/gui/x/xlib/events/processing-overview.html
##Keyboard Input To process keyboard input subscribe to three event masks KeyPressMask KeyReleaseMask and KeymapStateMask. The first two events will fire when a key is pressed or released. X handles mapping characters to key numbers, this mapping can change at any time if the user remaps keys. the KeyMask event is fired when the keymapping of the system changes.
Once subscribed to KeyPressMask | KeyReleaseMask | KeymapStateMask three events types will be fired, they are KeyPress, KeyRelease and KeymapNotify. Check the type variable of the XEvent object against these types.
In case the KeyMapNotify event is recieved, call the XRefreshKeyboardMapping(XMappingEvent* event_map); function. The function takes one argument, a XMappingEvent pointer.
If the KeyPress or KeyRelease events get fired use the int XLookupString(XKeyEvent *event_struct, char *buffer_return, int bytes_buffer, KeySym *keysym_return, XComposeStatus *status_in_out) function to translate the event into a KeySym (a KeySym is a typedef for an unsigned long coresponding to the keyID of the key pressed) and a string. buffer_return will hold the translated character string, keysym_return will hold the KeySym value. keysymdef.h holds a list of #define strings for each key.
###Sample Code (C++)
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysymdef.h>
#include <iostream>
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
printf("%s\n", "Could not open display");
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Open the window
window = XCreateSimpleWindow(display, RootWindowOfScreen(screen), 0, 0, 320, 200, 1, BlackPixel(display, screenId), WhitePixel(display, screenId));
XSelectInput(display, window, KeyPressMask | KeyReleaseMask | KeymapStateMask);
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
// Variables used in message loop
char str[25] = {0};
KeySym keysym = 0;
int len = 0;
bool running = true;
// Enter message loop
while (running) {
XNextEvent(display, &ev);
switch(ev.type) {
case KeymapNotify:
XRefreshKeyboardMapping(&ev.xmapping);
break;
case KeyPress:
len = XLookupString(&ev.xkey, str, 25, &keysym, NULL);
if (len > 0) {
std::cout << "Key pressed: " << str << " - " << len << " - " << keysym <<'\n';
}
if (keysym == XK_Escape) {
running = false;
}
break;
case KeyRelease:
len = XLookupString(&ev.xkey, str, 25, &keysym, NULL);
if (len > 0) {
std::cout << "Key released: " << str << " - " << len << " - " << keysym <<'\n';
}
break;
}
}
// Cleanup
XDestroyWindow(display, window);
XCloseDisplay(display);
return 1;
}
Compile the program using the following command line
LINUX: g++ -o XKeyIn XKeyIn.cpp -lX11 -L/usr/X11R6/lib -I/usr/X11R6/include
OSX: g++ -o XKeyIn XKeyIn.cpp -lX11 -L/usr/X11/lib -I/opt/X11/include
##Mouse Input To process mouse events subscribe to the PointerMotionMask, ButtonPressMask, ButtonReleaseMask, EnterWindowMask and LeaveWindowMask event masks. These masks will fire the following events: MotionNotify, ButtonPress, ButtonRelease, EnterNotify and LeaveNotify.
Masks:
PointerMotionMask | ButtonPressMask | ButtonReleaseMask | EnterWindowMask | LeaveWindowMask
On ButtonPress and ButtonRelease the event object will contains an xbutton field. This field has a button variable, which maps as follows: 1 - left mouse, 2 - middle mouse, 3 - right mouse, 4 - scroll up, 5 - scroll down.
On MotionNotify the event object will contain a xmotion field. This field has two variables x and y. The x and y variables contain the mouses position in window space.
###Sample Code (C++)
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysymdef.h>
#include <iostream>
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
printf("%s\n", "Could not open display");
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Open the window
window = XCreateSimpleWindow(display, RootWindowOfScreen(screen), 0, 0, 320, 200, 1, BlackPixel(display, screenId), WhitePixel(display, screenId));
XSelectInput(display, window, PointerMotionMask | ButtonPressMask | ButtonReleaseMask | EnterWindowMask | LeaveWindowMask);
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
// Variables used in message loop
bool running = true;
int x, y;
// Enter message loop
while (running) {
XNextEvent(display, &ev);
switch(ev.type) {
case ButtonPress:
if (ev.xbutton.button == 1) {
std::cout << "Left mouse down\n";
}
else if (ev.xbutton.button == 2) {
std::cout << "Middle mouse down\n";
}
else if (ev.xbutton.button == 3) {
std::cout << "Right mouse down\n";
}
else if (ev.xbutton.button == 4) {
std::cout << "Mouse scroll up\n";
}
else if (ev.xbutton.button == 5) {
std::cout << "Mouse scroll down\n";
}
break;
case ButtonRelease:
if (ev.xbutton.button == 1) {
std::cout << "Left mouse up\n";
}
else if (ev.xbutton.button == 2) {
std::cout << "Middle mouse up\n";
}
else if (ev.xbutton.button == 3) {
std::cout << "Right mouse up\n";
running = false;
}
break;
case MotionNotify:
x = ev.xmotion.x;
y = ev.xmotion.y;
std::cout << "Mouse X:" << x << ", Y: " << y << "\n";
break;
case EnterNotify:
std::cout << "Mouse enter\n";
break;
case LeaveNotify:
std::cout << "Mouse leave\n";
break;
}
}
// Cleanup
XDestroyWindow(display, window);
XCloseDisplay(display);
return 1;
}
##Window Size & Title
Set the window's title using the XStoreName(Display* d, Window w, char *window_name) function. The first argument is the display link, the second argument is the window object and the third argument is the new window title.
Query the size of the current window with the XGetWindowAttributes(Display* d, Window w, XWindowAttributes* winAttribs); function. The first argument is the display link, the second is the window object. The third argument is a XWindowAttributes object, this object has two fields width and height.
When a window is resized the Expose event is fired, listen for this event by subscribing the ExposureMask event mask. When processing the Expose event, query the window size with the XGetWindowAttributes funcion described above.
At runtime the width, height and position of the window can be changed with the XConfigureWindow(Display* d, Window w, uint value_mask, XWindowChanges *values; function. The first argument is the display link, the second argument is the window. The third argument is an unsigned int, this is a bitmask representing which fields of the fourth argument to use. The fourth argument is a pointer to a XWindowChanges structure. Valid values for the mask are: CWX, CWY, CWWidth, CWHeight, CWBorderWidth, CWSibling and CWStackMode. The XWindowChanges struct has the following fields: int x, y, int width, height, int border_width, Window sibling and int stack_mode.
###Sample Code (C++)
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysymdef.h>
#include <iostream>
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
printf("%s\n", "Could not open display");
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Open the window
window = XCreateSimpleWindow(display, RootWindowOfScreen(screen), 0, 0, 320, 200, 1, BlackPixel(display, screenId), WhitePixel(display, screenId));
XSelectInput(display, window, ExposureMask);
// Name the window
XStoreName(display, window, "Named Window");
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
// How large is the window
XWindowAttributes attribs;
XGetWindowAttributes(display, window, &attribs);
std::cout << "Window Width: " << attribs.width << ", Height: " << attribs.height << "\n";
// Resize window
unsigned int change_values = CWWidth | CWHeight;
XWindowChanges values;
values.width = 800;
values.height = 600;
XConfigureWindow(display, window, change_values, &values);
// Variables used in message loop
bool running = true;
int x, y;
// Enter message loop
while (running) {
XNextEvent(display, &ev);
switch(ev.type) {
case Expose:
std::cout << "Expose event fired\n";
XGetWindowAttributes(display, window, &attribs);
std::cout << "\tWindow Width: " << attribs.width << ", Height: " << attribs.height << "\n";
break;
}
}
// Cleanup
XDestroyWindow(display, window);
XCloseDisplay(display);
return 1;
}
#Part 3, OpenGL
OpenGL on X11 is done trough the X11 library, include the <GL/glx.h> header.
##Enabling OpenGL
Before showing the window with XMapRaised it's a good idea to check the version of GLX available. Note, the GLX version is not the same as the OpenGL version. This can be done with the glXQueryVersion(Display* display, GLint* major, GLint* minor) function. The first argument is a pointer to the display object, the second two arguments are integer pointer that will have the major and minor version number written to them. If the minimum version of OpenGL is not supported, exit the program. A good minimum verions is 1.2
GLint majorGLX, minorGLX = 0;
glXQueryVersion(display, &majorGLX, &minorGLX);
if (majorGLX <= 1 && minorGLX < 2) {
std::cout << "GLX 1.2 or greater is required.\n";
XCloseDisplay(display);
return 1;
}
else {
std::cout << "GLX version: " << majorGLX << "." << minorGLX << '\n';
}
To create an OpenGL window a XVisualInfo object is needed. This object describes the minimum requirements to create a window. It is created with the glXChooseVisual(Display *display, int screen, int *attribList) function. If a window matching these minimum requirements can not be created NULL is returned. The first argument is the display object, the second is the screen id. The third argument is an array of flags used for creating the window. The creation code below makes a double buffered window with a 24 bit depth and 8bit stencil buffer.
GLint glxAttribs[] = {
GLX_RGBA,
GLX_DOUBLEBUFFER,
GLX_DEPTH_SIZE, 24,
GLX_STENCIL_SIZE, 8,
GLX_RED_SIZE, 8,
GLX_GREEN_SIZE, 8,
GLX_BLUE_SIZE, 8,
GLX_SAMPLE_BUFFERS, 0,
GLX_SAMPLES, 0,
None
};
XVisualInfo* visual = glXChooseVisual(display, screenId, glxAttribs);
if (visual == 0) {
std::cout << "Could not create correct visual window.\n";
XCloseDisplay(display);
return 1;
}
When creating an OpenGL window the XCreateSimpleWindow function can no longer be used to create a window, instead the XCreateWindow(Display *display, Window parent, int x, int y, unsigned int width, unsigned int height, unsigned int border_width, int depth, unsigned int class, Visual *visual, unsigned long valuemask, XSetWindowAttributes *attributes); function must be used. The first argument is the display, the second argument is the parent of the window being created. Use the RootWindow(Display* display, int screen_number function to get this window. The x, y, width, height and border width paramaters are self explanatory. For the depth of the window use the depth field of the XVisualInfo class, the visual mask should be set to the InputOutput constant. Lastly a XSetWindowAttributes struct must be created. This struct describes all of the attributes the window will have. The following fields should be set: border_pixel, background_pixel, override_redirect, colormap and event_mask. The colormap field is very important, get it using the XCreateColormap(Display *display, Window w, Visual *visual, int alloc); function. The display and window are the same as always. The Visual object is contained within the visual field of the XVisualInfo object. Lastly the alloc argument should be set to the AllocNone constant.
XSetWindowAttributes windowAttribs;
windowAttribs.border_pixel = BlackPixel(display, screenId);
windowAttribs.background_pixel = WhitePixel(display, screenId);
windowAttribs.override_redirect = True;
windowAttribs.colormap = XCreateColormap(display, RootWindow(display, screenId), visual->visual, AllocNone);
windowAttribs.event_mask = ExposureMask;
window = XCreateWindow(display, RootWindow(display, screenId), 0, 0, 320, 200, 0, visual->depth, InputOutput, visual->visual, CWBackPixel | CWColormap | CWBorderPixel | CWEventMask, &windowAttribs);
After the window is created, an OpenGL context can be acquired with the glXCreateContext(Display* display, XVisualInfo* visual, GLXContext shareList, Bool direct); function. The display and visual are the objects from before. The share list should be NULL and the direct should be set to true. Make the context active with the glXMakeCurrent(Display* display, Window window, GLXContext context) function. After a context is active the glGetString function can be used to retrieve information about the active OpenGL instance.
GLXContext context = glXCreateContext(display, visual, NULL, GL_TRUE);
glXMakeCurrent(display, window, context);
std::cout << "GL Vendor: " << glGetString(GL_VENDOR) << "\n";
std::cout << "GL Renderer: " << glGetString(GL_RENDERER) << "\n";
std::cout << "GL Version: " << glGetString(GL_VERSION) << "\n";
std::cout << "GL Shading Language: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << "\n";
After a context is set active let the application enter it's update loop. Present the context of the active back buffer with the glXSwapBuffers(Display* display, Window window) function.
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f( 1.0f, 0.0f, 0.0f);
glVertex3f( 0.0f, -1.0f, 0.0f);
glColor3f( 0.0f, 1.0f, 0.0f);
glVertex3f(-1.0f, 1.0f, 0.0f);
glColor3f( 0.0f, 0.0f, 1.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glEnd();
// Present frame
glXSwapBuffers(display, window);
Finally, once the update loop has finishes the context must be destroyed with the glXDestroyContext(Display* display, GLXContext context) function. The Visual needs to be cleaned up with XFree and the display and color map association should be destroyed with XFreeColormap
###Sample Code (C++)
#include <iostream>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysymdef.h>
#include <GL/gl.h>
#include <GL/glx.h>
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
std::cout << "Could not open display\n";
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Check GLX version
GLint majorGLX, minorGLX = 0;
glXQueryVersion(display, &majorGLX, &minorGLX);
if (majorGLX <= 1 && minorGLX < 2) {
std::cout << "GLX 1.2 or greater is required.\n";
XCloseDisplay(display);
return 1;
}
else {
std::cout << "GLX version: " << majorGLX << "." << minorGLX << '\n';
}
// GLX, create XVisualInfo, this is the minimum visuals we want
GLint glxAttribs[] = {
GLX_RGBA,
GLX_DOUBLEBUFFER,
GLX_DEPTH_SIZE, 24,
GLX_STENCIL_SIZE, 8,
GLX_RED_SIZE, 8,
GLX_GREEN_SIZE, 8,
GLX_BLUE_SIZE, 8,
GLX_SAMPLE_BUFFERS, 0,
GLX_SAMPLES, 0,
None
};
XVisualInfo* visual = glXChooseVisual(display, screenId, glxAttribs);
if (visual == 0) {
std::cout << "Could not create correct visual window.\n";
XCloseDisplay(display);
return 1;
}
// Open the window
XSetWindowAttributes windowAttribs;
windowAttribs.border_pixel = BlackPixel(display, screenId);
windowAttribs.background_pixel = WhitePixel(display, screenId);
windowAttribs.override_redirect = True;
windowAttribs.colormap = XCreateColormap(display, RootWindow(display, screenId), visual->visual, AllocNone);
windowAttribs.event_mask = ExposureMask;
window = XCreateWindow(display, RootWindow(display, screenId), 0, 0, 320, 200, 0, visual->depth, InputOutput, visual->visual, CWBackPixel | CWColormap | CWBorderPixel | CWEventMask, &windowAttribs);
// Create GLX OpenGL context
GLXContext context = glXCreateContext(display, visual, NULL, GL_TRUE);
glXMakeCurrent(display, window, context);
std::cout << "GL Vendor: " << glGetString(GL_VENDOR) << "\n";
std::cout << "GL Renderer: " << glGetString(GL_RENDERER) << "\n";
std::cout << "GL Version: " << glGetString(GL_VERSION) << "\n";
std::cout << "GL Shading Language: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << "\n";
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
// Set GL Sample stuff
glClearColor(0.5f, 0.6f, 0.7f, 1.0f);
// Enter message loop
while (true) {
XNextEvent(display, &ev);
if (ev.type == Expose) {
XWindowAttributes attribs;
XGetWindowAttributes(display, window, &attribs);
glViewport(0, 0, attribs.width, attribs.height);
}
// OpenGL Rendering
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f( 1.0f, 0.0f, 0.0f);
glVertex3f( 0.0f, -1.0f, 0.0f);
glColor3f( 0.0f, 1.0f, 0.0f);
glVertex3f(-1.0f, 1.0f, 0.0f);
glColor3f( 0.0f, 0.0f, 1.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glEnd();
// Present frame
glXSwapBuffers(display, window);
}
// Cleanup GLX
glXDestroyContext(display, context);
// Cleanup X11
XFree(visual);
XFreeColormap(display, windowAttribs.colormap);
XDestroyWindow(display, window);
XCloseDisplay(display);
return 0;
}
##Getting a modern context
Finding information on how to get a modern OpenGL context on X11 was rather difficult. Much of this part is adapted from https://www.opengl.org/wiki/Tutorial:_OpenGL_3.0_Context_Creation_(GLX). First, lets define a type for the glXCreateContextAttribsARB function and create a function that checks for supported extensions, this function will take two arguments, the extension list and target extension that is being queried.
typedef GLXContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLXContext, Bool, const int*);
static bool isExtensionSupported(const char *extList, const char *extension) {
const char *start;
const char *where, *terminator;
/* Extension names should not have spaces. */
where = strchr(extension, ' ');
if (where || *extension == '\0')
return false;
/* It takes a bit of care to be fool-proof about parsing the
OpenGL extensions string. Don't be fooled by sub-strings,
etc. */
for (start=extList;;) {
where = strstr(start, extension);
if (!where) {
break;
}
terminator = where + strlen(extension);
if ( where == start || *(where - 1) == ' ' ) {
if ( *terminator == ' ' || *terminator == '\0' ) {
return true;
}
}
start = terminator;
}
return false;
}
The glxAttribs variable is going to be different for a modern context.
GLint glxAttribs[] = {
GLX_X_RENDERABLE , True,
GLX_DRAWABLE_TYPE , GLX_WINDOW_BIT,
GLX_RENDER_TYPE , GLX_RGBA_BIT,
GLX_X_VISUAL_TYPE , GLX_TRUE_COLOR,
GLX_RED_SIZE , 8,
GLX_GREEN_SIZE , 8,
GLX_BLUE_SIZE , 8,
GLX_ALPHA_SIZE , 8,
GLX_DEPTH_SIZE , 24,
GLX_STENCIL_SIZE , 8,
GLX_DOUBLEBUFFER , True,
None
;
Once the desired attributes are defined, a compatible frame buffer needs to be created. This is done with the glXChooseFBConfig(Display* display, int screen, GLint* attribs, int* outCount funciton. This function will return an array of framebuffer configuration objects, as good as or better than what was specified in the attribs field. After the array is acquired it's ok to use the first one in the array.
int fbcount;
GLXFBConfig* fbc = glXChooseFBConfig(display, DefaultScreen(display), glxAttribs, &fbcount);
if (fbc == 0) {
std::cout << "Failed to retrieve framebuffer.\n";
XCloseDisplay(display);
return 1;
}
std::cout << "Found " << fbcount << " matching framebuffers.\n";
glXChooseVisual can no longer be used to acquire a XVisualInfo object, instead glXGetVisualFromFBConfig(Display* display, GLXFBConfig fbConfig) must be used to take the best framebuffer into account.
XVisualInfo* visual = glXGetVisualFromFBConfig( display, bestFbc );
if (visual == 0) {
std::cout << "Could not create correct visual window.\n";
XCloseDisplay(display);
return 1;
}
A pointer to the glXCreateContextAttribsARB function needs to be acquired trough the glXGetProcAddressARB(const GLubyte * strFuncName) function.
glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddressARB( (const GLubyte *) "glXCreateContextAttribsARB" );
To actually create the new context use the glXCreateNewContext function, this function is only available if the GLX_ARB_create_context extension is present. If the glXCreateNewContext function is not avilable fall back on the glXCreateContextAttribsARB function, if that is not available either the legacy glXCreateContext is always an option.
int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
GLX_CONTEXT_MINOR_VERSION_ARB, 2,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
None
};
const char *glxExts = glXQueryExtensionsString( display, screenId );
GLXContext context = 0;
if (!isExtensionSupported( glxExts, "GLX_ARB_create_context")) {
context = glXCreateNewContext( display, bestFbc, GLX_RGBA_TYPE, 0, True );
}
else {
context = glXCreateContextAttribsARB( display, bestFbc, 0, true, context_attribs );
}
XSync( display, False );
It wouldn't make much sense to run a non direct OpenGL context for games, glx provides the glXIsDirect(Display* display, GLXContext context) function to check for this.
// Verifying that context is a direct context
if (!glXIsDirect (display, context)) {
std::cout << "Indirect GLX rendering context obtained\n";
}
else {
std::cout << "Direct GLX rendering context obtained\n";
}
###Sample Code (C++)
#include <iostream>
#include <cstring>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysymdef.h>
#include <GL/gl.h>
#include <GL/glx.h>
typedef GLXContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLXContext, Bool, const int*);
static bool isExtensionSupported(const char *extList, const char *extension) {
const char *start;
const char *where, *terminator;
where = strchr(extension, ' ');
if (where || *extension == '\0') {
return false;
}
for (start=extList;;) {
where = strstr(start, extension);
if (!where) {
break;
}
terminator = where + strlen(extension);
if ( where == start || *(where - 1) == ' ' ) {
if ( *terminator == ' ' || *terminator == '\0' ) {
return true;
}
}
start = terminator;
}
return false;
}
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
std::cout << "Could not open display\n";
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Check GLX version
GLint majorGLX, minorGLX = 0;
glXQueryVersion(display, &majorGLX, &minorGLX);
if (majorGLX <= 1 && minorGLX < 2) {
std::cout << "GLX 1.2 or greater is required.\n";
XCloseDisplay(display);
return 1;
}
else {
std::cout << "GLX client version: " << glXGetClientString(display, GLX_VERSION) << '\n';
std::cout << "GLX client vendor: " << glXGetClientString(display, GLX_VENDOR) << "\n";
std::cout << "GLX client extensions:\n\t" << glXGetClientString(display, GLX_EXTENSIONS) << "\n";
std::cout << "GLX server version: " << glXQueryServerString(display, screenId, GLX_VERSION) << "\n";
std::cout << "GLX server vendoe: " << glXQueryServerString(display, screenId, GLX_VENDOR) << "\n";
std::cout << "GLX server extensions:\n\t " << glXQueryServerString(display, screenId, GLX_EXTENSIONS) << "\n";
}
GLint glxAttribs[] = {
GLX_X_RENDERABLE , True,
GLX_DRAWABLE_TYPE , GLX_WINDOW_BIT,
GLX_RENDER_TYPE , GLX_RGBA_BIT,
GLX_X_VISUAL_TYPE , GLX_TRUE_COLOR,
GLX_RED_SIZE , 8,
GLX_GREEN_SIZE , 8,
GLX_BLUE_SIZE , 8,
GLX_ALPHA_SIZE , 8,
GLX_DEPTH_SIZE , 24,
GLX_STENCIL_SIZE , 8,
GLX_DOUBLEBUFFER , True,
None
};
int fbcount;
GLXFBConfig* fbc = glXChooseFBConfig(display, screenId, glxAttribs, &fbcount);
if (fbc == 0) {
std::cout << "Failed to retrieve framebuffer.\n";
XCloseDisplay(display);
return 1;
}
std::cout << "Found " << fbcount << " matching framebuffers.\n";
// Pick the FB config/visual with the most samples per pixel
std::cout << "Getting best XVisualInfo\n";
int best_fbc = -1, worst_fbc = -1, best_num_samp = -1, worst_num_samp = 999;
for (int i = 0; i < fbcount; ++i) {
XVisualInfo *vi = glXGetVisualFromFBConfig( display, fbc[i] );
if ( vi != 0) {
int samp_buf, samples;
glXGetFBConfigAttrib( display, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf );
glXGetFBConfigAttrib( display, fbc[i], GLX_SAMPLES , &samples );
//std::cout << " Matching fbconfig " << i << ", SAMPLE_BUFFERS = " << samp_buf << ", SAMPLES = " << samples << ".\n";
if ( best_fbc < 0 || (samp_buf && samples > best_num_samp) ) {
best_fbc = i;
best_num_samp = samples;
}
if ( worst_fbc < 0 || !samp_buf || samples < worst_num_samp )
worst_fbc = i;
worst_num_samp = samples;
}
XFree( vi );
}
std::cout << "Best visual info index: " << best_fbc << "\n";
GLXFBConfig bestFbc = fbc[ best_fbc ];
XFree( fbc ); // Make sure to free this!
XVisualInfo* visual = glXGetVisualFromFBConfig( display, bestFbc );
if (visual == 0) {
std::cout << "Could not create correct visual window.\n";
XCloseDisplay(display);
return 1;
}
if (screenId != visual->screen) {
std::cout << "screenId(" << screenId << ") does not match visual->screen(" << visual->screen << ").\n";
XCloseDisplay(display);
return 1;
}
// Open the window
XSetWindowAttributes windowAttribs;
windowAttribs.border_pixel = BlackPixel(display, screenId);
windowAttribs.background_pixel = WhitePixel(display, screenId);
windowAttribs.override_redirect = True;
windowAttribs.colormap = XCreateColormap(display, RootWindow(display, screenId), visual->visual, AllocNone);
windowAttribs.event_mask = ExposureMask;
window = XCreateWindow(display, RootWindow(display, screenId), 0, 0, 320, 200, 0, visual->depth, InputOutput, visual->visual, CWBackPixel | CWColormap | CWBorderPixel | CWEventMask, &windowAttribs);
// Create GLX OpenGL context
glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddressARB( (const GLubyte *) "glXCreateContextAttribsARB" );
const char *glxExts = glXQueryExtensionsString( display, screenId );
std::cout << "Late extensions:\n\t" << glxExts << "\n\n";
if (glXCreateContextAttribsARB == 0) {
std::cout << "glXCreateContextAttribsARB() not found.\n";
}
int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
GLX_CONTEXT_MINOR_VERSION_ARB, 2,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
None
};
GLXContext context = 0;
if (!isExtensionSupported( glxExts, "GLX_ARB_create_context")) {
context = glXCreateNewContext( display, bestFbc, GLX_RGBA_TYPE, 0, True );
}
else {
context = glXCreateContextAttribsARB( display, bestFbc, 0, true, context_attribs );
}
XSync( display, False );
// Verifying that context is a direct context
if (!glXIsDirect (display, context)) {
std::cout << "Indirect GLX rendering context obtained\n";
}
else {
std::cout << "Direct GLX rendering context obtained\n";
}
glXMakeCurrent(display, window, context);
std::cout << "GL Vendor: " << glGetString(GL_VENDOR) << "\n";
std::cout << "GL Renderer: " << glGetString(GL_RENDERER) << "\n";
std::cout << "GL Version: " << glGetString(GL_VERSION) << "\n";
std::cout << "GL Shading Language: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << "\n";
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
// Set GL Sample stuff
glClearColor(0.5f, 0.6f, 0.7f, 1.0f);
// Enter message loop
while (true) {
XNextEvent(display, &ev);
if (ev.type == Expose) {
XWindowAttributes attribs;
XGetWindowAttributes(display, window, &attribs);
glViewport(0, 0, attribs.width, attribs.height);
}
// OpenGL Rendering
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f( 1.0f, 0.0f, 0.0f);
glVertex3f( 0.0f, -1.0f, 0.0f);
glColor3f( 0.0f, 1.0f, 0.0f);
glVertex3f(-1.0f, 1.0f, 0.0f);
glColor3f( 0.0f, 0.0f, 1.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glEnd();
// Present frame
glXSwapBuffers(display, window);
}
// Cleanup GLX
glXDestroyContext(display, context);
// Cleanup X11
XFree(visual);
XFreeColormap(display, windowAttribs.colormap);
XDestroyWindow(display, window);
XCloseDisplay(display);
return 0;
}
#Part 4, Putting it all together Before putting all the pieces together, there is one more problem with the current implementation of the window. In order to close the window properly the DestroyNotify message needs to be handled. If DestroyNotify is recieved, the main loop should stop. To make the close button work, the DeleteWindow message must be treated as a client message; to remap it place the following code after the window was created, but before it is raised:
Atom atomWmDeleteWindow = XInternAtom(display, "WM_DELETE_WINDOW", False);
XSetWMProtocols(display, window, &atomWmDeleteWindow, 1);
After the DeleteWindow message has been remapped as a client message subscribe to StructureNotifyMask. Finally, make sure to handle the new cases in the message loop.
XNextEvent(display, &ev);
if (ev.type == ClientMessage) {
if (ev.xclient.data.l[0] == atomWmDeleteWindow) {
break;
}
}
else if (ev.type == DestroyNotify) {
break;
}
###Sample Code (C++)
#include <iostream>
#include <cstring>
#include <X11/Xlib.h>
#include <X11/Xutil.h>
#include <X11/keysymdef.h>
#include <GL/gl.h>
#include <GL/glx.h>
#include <sys/time.h>
#include <unistd.h>
#define WINDOW_WIDTH 800
#define WINDOW_HEIGHT 600
#define FPS 30
#define TEST_LOCAL
extern bool Initialize(int w, int h);
extern bool Update(float deltaTime);
extern void Render();
extern void Resize(int w, int h);
extern void Shutdown();
typedef GLXContext (*glXCreateContextAttribsARBProc)(Display*, GLXFBConfig, GLXContext, Bool, const int*);
#define SKIP_TICKS (1000 / FPS)
static double GetMilliseconds() {
static timeval s_tTimeVal;
gettimeofday(&s_tTimeVal, NULL);
double time = s_tTimeVal.tv_sec * 1000.0; // sec to ms
time += s_tTimeVal.tv_usec / 1000.0; // us to ms
return time;
}
static bool isExtensionSupported(const char *extList, const char *extension) {
return strstr(extList, extension) != 0;
}
int main(int argc, char** argv) {
Display* display;
Window window;
Screen* screen;
int screenId;
XEvent ev;
// Open the display
display = XOpenDisplay(NULL);
if (display == NULL) {
std::cout << "Could not open display\n";
return 1;
}
screen = DefaultScreenOfDisplay(display);
screenId = DefaultScreen(display);
// Check GLX version
GLint majorGLX, minorGLX = 0;
glXQueryVersion(display, &majorGLX, &minorGLX);
if (majorGLX <= 1 && minorGLX < 2) {
std::cout << "GLX 1.2 or greater is required.\n";
XCloseDisplay(display);
return 1;
}
GLint glxAttribs[] = {
GLX_X_RENDERABLE , True,
GLX_DRAWABLE_TYPE , GLX_WINDOW_BIT,
GLX_RENDER_TYPE , GLX_RGBA_BIT,
GLX_X_VISUAL_TYPE , GLX_TRUE_COLOR,
GLX_RED_SIZE , 8,
GLX_GREEN_SIZE , 8,
GLX_BLUE_SIZE , 8,
GLX_ALPHA_SIZE , 8,
GLX_DEPTH_SIZE , 24,
GLX_STENCIL_SIZE , 8,
GLX_DOUBLEBUFFER , True,
None
};
int fbcount;
GLXFBConfig* fbc = glXChooseFBConfig(display, screenId, glxAttribs, &fbcount);
if (fbc == 0) {
std::cout << "Failed to retrieve framebuffer.\n";
XCloseDisplay(display);
return 1;
}
// Pick the FB config/visual with the most samples per pixel
int best_fbc = -1, worst_fbc = -1, best_num_samp = -1, worst_num_samp = 999;
for (int i = 0; i < fbcount; ++i) {
XVisualInfo *vi = glXGetVisualFromFBConfig( display, fbc[i] );
if ( vi != 0) {
int samp_buf, samples;
glXGetFBConfigAttrib( display, fbc[i], GLX_SAMPLE_BUFFERS, &samp_buf );
glXGetFBConfigAttrib( display, fbc[i], GLX_SAMPLES , &samples );
if ( best_fbc < 0 || (samp_buf && samples > best_num_samp) ) {
best_fbc = i;
best_num_samp = samples;
}
if ( worst_fbc < 0 || !samp_buf || samples < worst_num_samp )
worst_fbc = i;
worst_num_samp = samples;
}
XFree( vi );
}
GLXFBConfig bestFbc = fbc[ best_fbc ];
XFree( fbc ); // Make sure to free this!
XVisualInfo* visual = glXGetVisualFromFBConfig( display, bestFbc );
if (visual == 0) {
std::cout << "Could not create correct visual window.\n";
XCloseDisplay(display);
return 1;
}
if (screenId != visual->screen) {
std::cout << "screenId(" << screenId << ") does not match visual->screen(" << visual->screen << ").\n";
XCloseDisplay(display);
return 1;
}
// Open the window
XSetWindowAttributes windowAttribs;
windowAttribs.border_pixel = BlackPixel(display, screenId);
windowAttribs.background_pixel = WhitePixel(display, screenId);
windowAttribs.override_redirect = True;
windowAttribs.colormap = XCreateColormap(display, RootWindow(display, screenId), visual->visual, AllocNone);
windowAttribs.event_mask = ExposureMask;
window = XCreateWindow(display, RootWindow(display, screenId), 0, 0, WINDOW_WIDTH, WINDOW_HEIGHT, 0, visual->depth, InputOutput, visual->visual, CWBackPixel | CWColormap | CWBorderPixel | CWEventMask, &windowAttribs);
// Redirect Close
Atom atomWmDeleteWindow = XInternAtom(display, "WM_DELETE_WINDOW", False);
XSetWMProtocols(display, window, &atomWmDeleteWindow, 1);
// Create GLX OpenGL context
glXCreateContextAttribsARBProc glXCreateContextAttribsARB = 0;
glXCreateContextAttribsARB = (glXCreateContextAttribsARBProc) glXGetProcAddressARB( (const GLubyte *) "glXCreateContextAttribsARB" );
int context_attribs[] = {
GLX_CONTEXT_MAJOR_VERSION_ARB, 3,
GLX_CONTEXT_MINOR_VERSION_ARB, 2,
GLX_CONTEXT_FLAGS_ARB, GLX_CONTEXT_FORWARD_COMPATIBLE_BIT_ARB,
None
};
GLXContext context = 0;
const char *glxExts = glXQueryExtensionsString( display, screenId );
if (!isExtensionSupported( glxExts, "GLX_ARB_create_context")) {
std::cout << "GLX_ARB_create_context not supported\n";
context = glXCreateNewContext( display, bestFbc, GLX_RGBA_TYPE, 0, True );
}
else {
context = glXCreateContextAttribsARB( display, bestFbc, 0, true, context_attribs );
}
XSync( display, False );
// Verifying that context is a direct context
if (!glXIsDirect (display, context)) {
std::cout << "Indirect GLX rendering context obtained\n";
}
else {
std::cout << "Direct GLX rendering context obtained\n";
}
glXMakeCurrent(display, window, context);
std::cout << "GL Renderer: " << glGetString(GL_RENDERER) << "\n";
std::cout << "GL Version: " << glGetString(GL_VERSION) << "\n";
std::cout << "GLSL Version: " << glGetString(GL_SHADING_LANGUAGE_VERSION) << "\n";
if (!Initialize(WINDOW_WIDTH, WINDOW_HEIGHT)) {
glXDestroyContext(display, context);
XFree(visual);
XFreeColormap(display, windowAttribs.colormap);
XDestroyWindow(display, window);
XCloseDisplay(display);
return 1;
}
// Show the window
XClearWindow(display, window);
XMapRaised(display, window);
double prevTime = GetMilliseconds();
double currentTime = GetMilliseconds();
double deltaTime = 0.0;
timeval time;
long sleepTime = 0;
gettimeofday(&time, NULL);
long nextGameTick = (time.tv_sec * 1000) + (time.tv_usec / 1000);
// Enter message loop
while (true) {
if (XPending(display) > 0) {
XNextEvent(display, &ev);
if (ev.type == Expose) {
XWindowAttributes attribs;
XGetWindowAttributes(display, window, &attribs);
Resize(attribs.width, attribs.height);
}
if (ev.type == ClientMessage) {
if (ev.xclient.data.l[0] == atomWmDeleteWindow) {
break;
}
}
else if (ev.type == DestroyNotify) {
break;
}
}
currentTime = GetMilliseconds();
deltaTime = double(currentTime - prevTime) * 0.001;
prevTime = currentTime;
if (!Update((float)deltaTime)) {
break;
}
Render();
// Present frame
glXSwapBuffers(display, window);
gettimeofday(&time, NULL);
nextGameTick += SKIP_TICKS;
sleepTime = nextGameTick - ((time.tv_sec * 1000) + (time.tv_usec / 1000));
usleep((unsigned int)(sleepTime / 1000));
}
std::cout << "Shutting Down\n";
Shutdown();
// Cleanup GLX
glXDestroyContext(display, context);
// Cleanup X11
XFree(visual);
XFreeColormap(display, windowAttribs.colormap);
XDestroyWindow(display, window);
XCloseDisplay(display);
return 0;
}
#ifdef TEST_LOCAL
bool Initialize(int w, int h) {
glClearColor(0.5f, 0.6f, 0.7f, 1.0f);
glViewport(0, 0, w, h);
return true;
}
bool Update(float deltaTime) {
return true;
}
void Render() {
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_TRIANGLES);
glColor3f( 1.0f, 0.0f, 0.0f);
glVertex3f( 0.0f, -1.0f, 0.0f);
glColor3f( 0.0f, 1.0f, 0.0f);
glVertex3f(-1.0f, 1.0f, 0.0f);
glColor3f( 0.0f, 0.0f, 1.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glEnd();
}
void Resize(int w, int h) {
glViewport(0, 0, w, h);
}
void Shutdown() {
}
#endif
#Sources There is a lot of disjoint information floating around the internet about X11. These are the sources i've used to put together this article.
- http://xopendisplay.hilltopia.ca/2009/Jan/Xlib-tutorial-part-1----Beginnings.html
- http://tronche.com/gui/x/xlib/display/opening.html
- http://techpubs.sgi.com/library/dynaweb_docs/0640/SGI_Developer/books/OpenGL_Porting/sgi_html/ch04.html
- http://www.unix-manuals.com/tutorials/xlib/xlib.html
- http://nehe.gamedev.net/tutorial/simpleglxwindow_class/35003/
- http://tronche.com/gui/x/xlib/events/keyboard-pointer/keyboard-pointer.html
- https://github.com/blackberry/GamePlay/blob/master/gameplay%2Fsrc%2FPlatformLinux.cpp
- http://www-h.eng.cam.ac.uk/help/tpl/graphics/X/X11R5/node25.html
- http://tronche.com/gui/x/xlib/input/pointer-grabbing.html
- https://github.com/gameplay3d/GamePlay/blob/master/gameplay%2Fsrc%2FPlatformLinux.cpp
- http://tronche.com/gui/x/xlib/ICC/client-to-window-manager/XStoreName.html
- http://tronche.com/gui/x/xlib/window/configure.html#XWindowChanges
- http://tronche.com/gui/x/xlib/window/XConfigureWindow.html
- http://www.x.org/archive/X11R7.5/doc/man/man3/XVisualInfo.3.html
- http://msdn.microsoft.com/en-us/library/windows/desktop/dd318252(v=vs.85).aspx
- https://gist.github.com/kovrov/1304027
- https://www.youtube.com/watch?v=qWiqRIoKChg
- https://www.opengl.org/wiki/Tutorial:_OpenGL_3.0_Context_Creation_(GLX)