OpenGL newbie seeks help!

Hey /prog/, I'm writing a cross-platform OpenGL application which does some off-screen rendering. I've found two ways of doing that - with pbuffers and with FBOs, the latter is preferable. I want old videocards to be supported too.
Now tell me, which technique should I use? Do the older videocards support FBO? Do they support pbuffers?
Thanks.

>>12
MSDOS:

(uint8_t*)0xA0000000 = Color;

Linux/OpenGL

#include <stdio.h>
#include <GL/glx.h>
#include <GL/gl.h>
#include <GL/glu.h>
#include <X11/extensions/xf86vmode.h>
#include <X11/keysym.h>

/* stuff about our window grouped together */
typedef struct {
    Display *dpy;
    int screen;
    Window win;
    GLXContext ctx;
    XSetWindowAttributes attr;
    Bool fs;
    Bool doubleBuffered;
    XF86VidModeModeInfo deskMode;
    int x, y;
    unsigned int width, height;
    unsigned int depth;   
} GLWindow;

/* attributes for a single buffered visual in RGBA format with at least
 * 4 bits per color and a 16 bit depth buffer */
static int attrListSgl[] = {GLX_RGBA, GLX_RED_SIZE, 4,
    GLX_GREEN_SIZE, 4,
    GLX_BLUE_SIZE, 4,
    GLX_DEPTH_SIZE, 16,
    None};

/* attributes for a double buffered visual in RGBA format with at least
 * 4 bits per color and a 16 bit depth buffer */
static int attrListDbl[] = { GLX_RGBA, GLX_DOUBLEBUFFER,
    GLX_RED_SIZE, 4,
    GLX_GREEN_SIZE, 4,
    GLX_BLUE_SIZE, 4,
    GLX_DEPTH_SIZE, 16,
    None };

GLWindow GLWin;

/* function called when our window is resized (should only happen in window mode) */
void resizeGLScene(unsigned int width, unsigned int height)
{
    if (height == 0)    /* Prevent A Divide By Zero If The Window Is Too Small */
        height = 1;
    glViewport(0, 0, width, height);    /* Reset The Current Viewport And Perspective Transformation */
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0f, (GLfloat)width / (GLfloat)height, 0.1f, 100.0f);
    glMatrixMode(GL_MODELVIEW);
}

/* general OpenGL initialization function */
int initGL(GLvoid)
{
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
    glClearDepth(1.0f);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
    glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
    /* we use resizeGLScene once to set up our initial perspective */
    resizeGLScene(GLWin.width, GLWin.height);
    glFlush();
    return True;
}

/* Here goes our drawing code */
int drawGLScene(GLvoid)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    if (GLWin.doubleBuffered)
    {
        glXSwapBuffers(GLWin.dpy, GLWin.win);
    }
    return True;   
}

/* function to release/destroy our resources and restoring the old desktop */
GLvoid killGLWindow(GLvoid)
{
    if (GLWin.ctx)
    {
        if (!glXMakeCurrent(GLWin.dpy, None, NULL))
        {
            printf("Could not release drawing context.\n");
        }
        glXDestroyContext(GLWin.dpy, GLWin.ctx);
        GLWin.ctx = NULL;
    }
    /* switch back to original desktop resolution if we were in fs */
    if (GLWin.fs)
    {
        XF86VidModeSwitchToMode(GLWin.dpy, GLWin.screen, &GLWin.deskMode);
        XF86VidModeSetViewPort(GLWin.dpy, GLWin.screen, 0, 0);
    }
    XCloseDisplay(GLWin.dpy);
}

/* this function creates our window and sets it up properly */
/* FIXME: bits is currently unused */
Bool createGLWindow(char* title, int width, int height, int bits,
                    Bool fullscreenflag)
{
    XVisualInfo *vi;
    Colormap cmap;
    int dpyWidth, dpyHeight;
    int i;
    int glxMajorVersion, glxMinorVersion;
    int vidModeMajorVersion, vidModeMinorVersion;
    XF86VidModeModeInfo **modes;
    int modeNum;
    int bestMode;
    Atom wmDelete;
    Window winDummy;
    unsigned int borderDummy;
   
    GLWin.fs = fullscreenflag;
    /* set best mode to current */
    bestMode = 0;
    /* get a connection */
    GLWin.dpy = XOpenDisplay(0);
    GLWin.screen = DefaultScreen(GLWin.dpy);
    XF86VidModeQueryVersion(GLWin.dpy, &vidModeMajorVersion,
        &vidModeMinorVersion);
    printf("XF86VidModeExtension-Version %d.%d\n", vidModeMajorVersion,
        vidModeMinorVersion);
    XF86VidModeGetAllModeLines(GLWin.dpy, GLWin.screen, &modeNum, &modes);
    /* save desktop-resolution before switching modes */
    GLWin.deskMode = *modes[0];
    /* look for mode with requested resolution */
    for (i = 0; i < modeNum; i++)
    {
        if ((modes[i]->hdisplay == width) && (modes[i]->vdisplay == height))
        {
            bestMode = i;
        }
    }
    /* get an appropriate visual */
    vi = glXChooseVisual(GLWin.dpy, GLWin.screen, attrListDbl);
    if (vi == NULL)
    {
        vi = glXChooseVisual(GLWin.dpy, GLWin.screen, attrListSgl);
        GLWin.doubleBuffered = False;
        printf("Only Singlebuffered Visual!\n");
    }
    else
    {
        GLWin.doubleBuffered = True;
        printf("Got Doublebuffered Visual!\n");
    }
    glXQueryVersion(GLWin.dpy, &glxMajorVersion, &glxMinorVersion);
    printf("glX-Version %d.%d\n", glxMajorVersion, glxMinorVersion);
    /* create a GLX context */
    GLWin.ctx = glXCreateContext(GLWin.dpy, vi, 0, GL_TRUE);
    /* create a color map */
    cmap = XCreateColormap(GLWin.dpy, RootWindow(GLWin.dpy, vi->screen),
        vi->visual, AllocNone);
    GLWin.attr.colormap = cmap;
    GLWin.attr.border_pixel = 0;

    if (GLWin.fs)
    {
        XF86VidModeSwitchToMode(GLWin.dpy, GLWin.screen, modes[bestMode]);
        XF86VidModeSetViewPort(GLWin.dpy, GLWin.screen, 0, 0);
        dpyWidth = modes[bestMode]->hdisplay;
        dpyHeight = modes[bestMode]->vdisplay;
        printf("Resolution %dx%d\n", dpyWidth, dpyHeight);
        XFree(modes);
..