progs/xdemos/offset.c

/****************************************************************************
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, 
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****************************************************************************/

/*
 * 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;
}