“Hello World” OpenGL on Linux

“Hello World” OpenGL on Linux

Writing the OpenGL context creation plumbing on Linux isn’t 100% intuitive. It’s always good to have a handy getting started guide. With developers increasingly using engines such as Unity, the number of people writing directly to OpenGL is shrinking – and so are some of the online resources to get over this initial step. I decided to collect a few links and copy critical sample code here for when I need to whip something up quickly.

 

Some links to good ‘hello world’ Linux GL samples:
https://github.com/jckarter/hello-gl
https://www.opengl.org/wiki/Tutorial:_OpenGL_3.0_Context_Creation_(GLX)
http://www-f9.ijs.si/~matevz/docs/007-2392-003/sgi_html/ch04.html

 

Code:
Taken from: https://www.opengl.org/sdk/docs/man2/xhtml/glXIntro.xml

Below is a minimal example of creating an RGBA-format X window that’s compatible with OpenGL using GLX 1.3 commands. The window is cleared to yellow when the program runs. The program does minimal error checking; all return values should be checked.

#include < stdio.h >
#include < stdlib.h >
#include < GL/gl.h >
#include < GL/glx.h >

int singleBufferAttributess[] = {
    GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
    GLX_RENDER_TYPE,   GLX_RGBA_BIT,
    GLX_RED_SIZE,      1,   /* Request a single buffered color buffer */
    GLX_GREEN_SIZE,    1,   /* with the maximum number of color bits  */
    GLX_BLUE_SIZE,     1,   /* for each component                     */
    None
};

int doubleBufferAttributes[] = {
    GLX_DRAWABLE_TYPE, GLX_WINDOW_BIT,
    GLX_RENDER_TYPE,   GLX_RGBA_BIT,
    GLX_DOUBLEBUFFER,  True,  /* Request a double-buffered color buffer with */
    GLX_RED_SIZE,      1,     /* the maximum number of bits per component    */
    GLX_GREEN_SIZE,    1, 
    GLX_BLUE_SIZE,     1,
    None
};


static Bool WaitForNotify( Display *dpy, XEvent *event, XPointer arg ) {
    return (event->type == MapNotify) && (event->xmap.window == (Window) arg);
}
int main( int argc, char *argv[] )
{
    Display              *dpy;
    Window                xWin;
    XEvent                event;
    XVisualInfo          *vInfo;
    XSetWindowAttributes  swa;
    GLXFBConfig          *fbConfigs;
    GLXContext            context;
    GLXWindow             glxWin;
    int                   swaMask;
    int                   numReturned;
    int                   swapFlag = True;

    /* Open a connection to the X server */
    dpy = XOpenDisplay( NULL );
    if ( dpy == NULL ) {
        printf( "Unable to open a connection to the X servern" );
        exit( EXIT_FAILURE );
    }

    /* Request a suitable framebuffer configuration - try for a double 
    ** buffered configuration first */
    fbConfigs = glXChooseFBConfig( dpy, DefaultScreen(dpy),
                                   doubleBufferAttributes, &numReturned );

    if ( fbConfigs == NULL ) {  /* no double buffered configs available */
      fbConfigs = glXChooseFBConfig( dpy, DefaultScreen(dpy),
                                     singleBufferAttributess, &numReturned );
      swapFlag = False;
    }

    /* Create an X colormap and window with a visual matching the first
    ** returned framebuffer config */
    vInfo = glXGetVisualFromFBConfig( dpy, fbConfigs[0] );

    swa.border_pixel = 0;
    swa.event_mask = StructureNotifyMask;
    swa.colormap = XCreateColormap( dpy, RootWindow(dpy, vInfo->screen),
                                    vInfo->visual, AllocNone );

    swaMask = CWBorderPixel | CWColormap | CWEventMask;

    xWin = XCreateWindow( dpy, RootWindow(dpy, vInfo->screen), 0, 0, 256, 256,
                          0, vInfo->depth, InputOutput, vInfo->visual,
                          swaMask, &swa );

    /* Create a GLX context for OpenGL rendering */
    context = glXCreateNewContext( dpy, fbConfigs[0], GLX_RGBA_TYPE,
				 NULL, True );

    /* Create a GLX window to associate the frame buffer configuration
    ** with the created X window */
    glxWin = glXCreateWindow( dpy, fbConfigs[0], xWin, NULL );
    
    /* Map the window to the screen, and wait for it to appear */
    XMapWindow( dpy, xWin );
    XIfEvent( dpy, &event, WaitForNotify, (XPointer) xWin );

    /* Bind the GLX context to the Window */
    glXMakeContextCurrent( dpy, glxWin, glxWin, context );

    /* OpenGL rendering ... */
    glClearColor( 1.0, 1.0, 0.0, 1.0 );
    glClear( GL_COLOR_BUFFER_BIT );

    glFlush();
    
    if ( swapFlag )
        glXSwapBuffers( dpy, glxWin );

    sleep( 10 );
    exit( EXIT_SUCCESS );
}

 

Leave a Reply

Your email address will not be published. Required fields are marked *