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diff --git a/progs/xdemos/offset.c b/progs/xdemos/offset.c
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+/****************************************************************************
+Copyright 1995 by Silicon Graphics Incorporated, Mountain View, California.
+
+                        All Rights Reserved
+
+Permission to use, copy, modify, and distribute this software and its 
+documentation for any purpose and without fee is hereby granted, 
+provided that the above copyright notice appear in all copies and that
+both that copyright notice and this permission notice appear in 
+supporting documentation, and that the name of Silicon Graphics not be
+used in advertising or publicity pertaining to distribution of the
+software without specific, written prior permission.  
+
+SILICON GRAPHICS DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE,
+INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO
+EVENT SHALL SILICON GRAPHICS BE LIABLE FOR ANY SPECIAL, INDIRECT OR
+CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF
+USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR
+OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.
+
+****************************************************************************/
+
+/*
+ * Derived from code written by Kurt Akeley, November 1992
+ *
+ *	Uses PolygonOffset to draw hidden-line images.  PolygonOffset
+ *	    shifts the z values of polygons an amount that is
+ *	    proportional to their slope in screen z.  This keeps
+ *	    the lines, which are drawn without displacement, from
+ *	    interacting with their respective polygons, and
+ *	    thus eliminates line dropouts.
+ *
+ *	The left image shows an ordinary antialiased wireframe image.
+ *	The center image shows an antialiased hidden-line image without
+ *	    PolygonOffset.
+ *	The right image shows an antialiased hidden-line image using
+ *	    PolygonOffset to reduce artifacts.
+ *
+ *	Drag with a mouse button pressed to rotate the models.
+ *	Press the escape key to exit.
+ */
+
+/*
+ * Modified for OpenGL 1.1 glPolygonOffset() conventions
+ */
+
+
+#include <GL/glx.h>
+#include <GL/glu.h>
+#include <X11/keysym.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+
+/*#undef GL_EXT_polygon_offset   uncomment to use new version*/
+
+
+#ifndef EXIT_FAILURE
+#  define EXIT_FAILURE    1
+#endif
+#ifndef EXIT_SUCCESS
+#  define EXIT_SUCCESS    0
+#endif
+
+#define MAXQUAD 6
+
+typedef float Vertex[3];
+
+typedef Vertex Quad[4];
+
+/* data to define the six faces of a unit cube */
+Quad quads[MAXQUAD] = {
+   { {0,0,0}, {1,0,0}, {1,1,0}, {0,1,0} },
+   { {0,0,1}, {1,0,1}, {1,1,1}, {0,1,1} },
+   { {0,0,0}, {1,0,0}, {1,0,1}, {0,0,1} },
+   { {0,1,0}, {1,1,0}, {1,1,1}, {0,1,1} },
+   { {0,0,0}, {0,0,1}, {0,1,1}, {0,1,0} },
+   { {1,0,0}, {1,0,1}, {1,1,1}, {1,1,0} }
+};
+
+#define WIREFRAME	0
+#define HIDDEN_LINE	1
+
+static void error(const char* prog, const char* msg);
+static void cubes(int mx, int my, int mode);
+static void fill(Quad quad);
+static void outline(Quad quad);
+static void draw_hidden(Quad quad, int mode);
+static void process_input(Display *dpy, Window win);
+static int query_extension(char* extName);
+
+static int attributeList[] = { GLX_RGBA, GLX_RED_SIZE, 1, GLX_GREEN_SIZE, 1,
+    GLX_BLUE_SIZE, 1, GLX_DOUBLEBUFFER, GLX_DEPTH_SIZE, 1, None };
+
+static int dimension = 3;
+
+int main(int argc, char** argv) {
+    Display *dpy;
+    XVisualInfo *vi;
+    XSetWindowAttributes swa;
+    Window win;
+    GLXContext cx;
+
+    dpy = XOpenDisplay(0);
+    if (!dpy) error(argv[0], "can't open display");
+
+    vi = glXChooseVisual(dpy, DefaultScreen(dpy), attributeList);
+    if (!vi) error(argv[0], "no suitable visual");
+
+    cx = glXCreateContext(dpy, vi, 0, GL_TRUE);
+
+    swa.colormap = XCreateColormap(dpy, RootWindow(dpy, vi->screen),
+                                   vi->visual, AllocNone);
+
+    swa.border_pixel = 0;
+    swa.event_mask = ExposureMask | StructureNotifyMask | KeyPressMask |
+	ButtonPressMask | ButtonMotionMask;
+    win = XCreateWindow(dpy, RootWindow(dpy, vi->screen), 0, 0, 900, 300,
+			0, vi->depth, InputOutput, vi->visual,
+			CWBorderPixel|CWColormap|CWEventMask, &swa);
+    XStoreName(dpy, win, "hiddenline");
+    XMapWindow(dpy, win);
+
+    glXMakeCurrent(dpy, win, cx);
+
+    /* check for the polygon offset extension */
+#ifndef GL_VERSION_1_1
+    if (!query_extension("GL_EXT_polygon_offset"))
+        error(argv[0], "polygon_offset extension is not available");
+#else
+   (void) query_extension;
+#endif
+
+    /* set up viewing parameters */
+    glMatrixMode(GL_PROJECTION);
+    gluPerspective(20, 1, 0.1, 20);
+    glMatrixMode(GL_MODELVIEW);
+    glTranslatef(0, 0, -15);
+
+    /* set other relevant state information */
+    glEnable(GL_DEPTH_TEST);
+
+#ifdef GL_EXT_polygon_offset
+    printf("using 1.0 offset extension\n");
+    glPolygonOffsetEXT( 1.0, 0.00001 );
+#else
+    printf("using 1.1 offset\n");
+    glPolygonOffset( 1.0, 0.5 );
+#endif
+
+    glShadeModel( GL_FLAT );
+    glDisable( GL_DITHER );
+
+    /* process events until the user presses ESC */
+    while (1) process_input(dpy, win);
+
+    return 0;
+}
+
+static void
+draw_scene(int mx, int my) {
+    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+
+    glPushMatrix();
+    glTranslatef(-1.7, 0.0, 0.0);
+    cubes(mx, my, WIREFRAME);
+    glPopMatrix();
+
+    glPushMatrix();
+    cubes(mx, my, HIDDEN_LINE);
+    glPopMatrix();
+
+    glPushMatrix();
+    glTranslatef(1.7, 0.0, 0.0);
+#ifdef GL_EXT_polygon_offset
+    glEnable(GL_POLYGON_OFFSET_EXT);
+#else
+    glEnable(GL_POLYGON_OFFSET_FILL);
+#endif
+    cubes(mx, my, HIDDEN_LINE);
+#ifdef GL_EXT_polygon_offset
+    glDisable(GL_POLYGON_OFFSET_EXT);
+#else
+    glDisable(GL_POLYGON_OFFSET_FILL);
+#endif
+    glPopMatrix();
+}
+
+
+static void
+cubes(int mx, int my, int mode) {
+    int x, y, z, i;
+
+    /* track the mouse */
+    glRotatef(mx / 2.0, 0, 1, 0);
+    glRotatef(my / 2.0, 1, 0, 0);
+
+    /* draw the lines as hidden polygons */
+    glTranslatef(-0.5, -0.5, -0.5);
+    glScalef(1.0/dimension, 1.0/dimension, 1.0/dimension);
+    for (z = 0; z < dimension; z++) {
+	for (y = 0; y < dimension; y++) {
+	    for (x = 0; x < dimension; x++) {
+		glPushMatrix();
+		glTranslatef(x, y, z);
+		glScalef(0.8, 0.8, 0.8);
+		for (i = 0; i < MAXQUAD; i++)
+		    draw_hidden(quads[i], mode);
+		glPopMatrix();
+	    }
+	}
+    }
+}
+
+static void
+fill(Quad quad) {
+    /* draw a filled polygon */
+    glBegin(GL_QUADS);
+    glVertex3fv(quad[0]);
+    glVertex3fv(quad[1]);
+    glVertex3fv(quad[2]);
+    glVertex3fv(quad[3]);
+    glEnd();
+}
+
+static void
+outline(Quad quad) {
+    /* draw an outlined polygon */
+    glBegin(GL_LINE_LOOP);
+    glVertex3fv(quad[0]);
+    glVertex3fv(quad[1]);
+    glVertex3fv(quad[2]);
+    glVertex3fv(quad[3]);
+    glEnd();
+}
+
+static void
+draw_hidden(Quad quad, int mode) {
+    if (mode == HIDDEN_LINE) {
+	glColor3f(0, 0, 0);
+	fill(quad);
+    }
+
+    /* draw the outline using white, optionally fill the interior with black */
+    glColor3f(1, 1, 1);
+    outline(quad);
+}
+
+static void
+process_input(Display *dpy, Window win) {
+    XEvent event;
+    static int prevx, prevy;
+    static int deltax = 90, deltay = 40;
+
+    do {
+	char buf[31];
+	KeySym keysym;
+
+	XNextEvent(dpy, &event);
+	switch(event.type) {
+	case Expose:
+	    break;
+	case ConfigureNotify: {
+	    /* this approach preserves a 1:1 viewport aspect ratio */
+	    int vX, vY, vW, vH;
+	    int eW = event.xconfigure.width, eH = event.xconfigure.height;
+	    if (eW >= eH) {
+		vX = 0;
+		vY = (eH - eW) >> 1;
+		vW = vH = eW;
+	    } else {
+		vX = (eW - eH) >> 1;
+		vY = 0;
+		vW = vH = eH;
+	    }
+	    glViewport(vX, vY, vW, vH);
+	    }
+	    break;
+	case KeyPress:
+	    (void) XLookupString(&event.xkey, buf, sizeof(buf), &keysym, NULL);
+	    switch (keysym) {
+	    case XK_Escape:
+		exit(EXIT_SUCCESS);
+	    default:
+		break;
+	    }
+	case ButtonPress:
+	    prevx = event.xbutton.x;
+	    prevy = event.xbutton.y;
+	    break;
+	case MotionNotify:
+	    deltax += (event.xbutton.x - prevx); prevx = event.xbutton.x;
+	    deltay += (event.xbutton.y - prevy); prevy = event.xbutton.y;
+	    break;
+	default:
+	    break;
+	}
+    } while (XPending(dpy));
+
+    draw_scene(deltax, deltay);
+    glXSwapBuffers(dpy, win);
+}
+
+static void
+error(const char *prog, const char *msg) {
+    fprintf(stderr, "%s: %s\n", prog, msg);
+    exit(EXIT_FAILURE);
+}
+
+static int
+query_extension(char* extName) {
+    char *p = (char *) glGetString(GL_EXTENSIONS);
+    char *end = p + strlen(p);
+    while (p < end) {
+        int n = strcspn(p, " ");
+        if ((strlen(extName) == n) && (strncmp(extName, p, n) == 0))
+            return GL_TRUE;
+        p += (n + 1);
+    }
+    return GL_FALSE;
+}
+