path: root/progs/xdemos/offset.c

/****************************************************************************
Copyright 1995 by Silicon Graphics Incorporated, Mountain View, California.

                        All Rights Reserved

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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 <X11/keysym.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

#undef GL_EXT_polygon_offset  /* use GL 1.1 version instead of extension */


#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}, {0,0,1}, {0,1,1}, {0,1,0} }, /* x = 0 */
   { {0,0,0}, {1,0,0}, {1,0,1}, {0,0,1} }, /* y = 0 */
   { {0,0,0}, {1,0,0}, {1,1,0}, {0,1,0} }, /* z = 0 */
   { {1,0,0}, {1,0,1}, {1,1,1}, {1,1,0} }, /* x = 1 */
   { {0,1,0}, {1,1,0}, {1,1,1}, {0,1,1} }, /* y = 1 */
   { {0,0,1}, {1,0,1}, {1,1,1}, {0,1,1} }  /* z = 1 */
};

#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, int face);
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;
    GLint z;

    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);
    glFrustum(-1, 1, -1, 1, 6, 20);
    glMatrixMode(GL_MODELVIEW);
    glTranslatef(0, 0, -15);

    /* set other relevant state information */
    glEnable(GL_DEPTH_TEST);

    glGetIntegerv(GL_DEPTH_BITS, &z);
    printf("GL_DEPTH_BITS = %d\n", z);

#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) {
   glClearColor(0.25, 0.25, 0.25, 0);
    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, i);
		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, int face) {
    static const GLfloat colors[3][3] = {
        {0.5, 0.5, 0.0},
        {0.8, 0.5, 0.0},
        {0.0, 0.5, 0.8}
    };
    if (mode == HIDDEN_LINE) {
        glColor3fv(colors[face % 3]);
	fill(quad);
    }

    /* draw the outline using white */
    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;
}