[9fans] Popi image viewer

[9fans] Popi image viewer

[Skip Tavakkolian]

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I wrote this to view images generated using popi.  It is really
trivial, thanks to Plan9's graphics model and the sane image format.
You'll notice most of the logic is for halftone conversion which is
completely unnecessary for Plan9, but interesting.  I did it to
understand draw() and company.

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// Displays popi generated images on Plan9 4th/ed.
// Popi information can be found at:
// http://cm.bell-labs.com/cm/cs/who/gerard/
//
// bugs are mine fst@centurytel.net

#include	<u.h>
#include	<libc.h>
#include	<draw.h>
#include	<event.h>
#include	<bio.h>
#include	"popi.h"

// Thresholds for halftone conversion from 8bit grayscale
// See "Beyond Photography, The digital Darkroom", G.J. Holtzmann
#define RES 8
uchar threshold[RES][RES] = {
	{ 0,128,32,160,8,136,40,168},
	{ 192,64,224,96,200,72,232,104 },
	{ 48,176,16,144,56,184,24,152 },
	{ 240,112,208,80,248,120,216,88 },
	{ 12,140,44,172,4,132,36,164 },
	{ 204,76,236,108,196,68,228,100 },
	{ 60,188,28,156,52,180,20,148 },
	{ 252,124,220,92,244,116,212,84 }
};

void usage(void)
{
	fprint(2, "usage: disp [-h] imagefile\n");
	fprint(2, "\timagefile is generated by popi\n");
	exits("usage");
}

void eresized(int x)
{
}

int main(int argc, char **argv)
{
	Biobufhdr *infile;
	int nr, hflag = 0;
	uchar g8[DEF_Y * DEF_X];	/* grey scale buffer */
	uchar g1[DEF_Y * DEF_X/8];	/* halftone buffer, 1 bit per pixel*/
	Image *dpic;
	Event ev;
	Rectangle r, R = Rect(0,0,DEF_X,DEF_Y);

	ARGBEGIN {
	case 'h':		/* halftone display */
		hflag = 1;
		break;
	default:
		usage();
	} ARGEND

	if (argc < 1) {
		fprint(2, "imagefile missing\n");
		usage();
	}
	if (! (infile = Bopen(argv[0], OREAD))) {
		fprint(2, "can't open %s: %r\n", argv[0]);
		usage();
	}

	initdraw(nil, nil, "disp");
	einit(Ekeyboard|Emouse);

	dpic = allocimage(display, R, (hflag) ? GREY1 : GREY8, 1, DWhite);

	/* popi image files are DEF_Y×DEF_X×8bit grayscale pixels */
	nr = DEF_Y * DEF_X;
	if (Bread(infile, g8, nr) != nr) {
		fprint(2, "bad popi image file\n");
		usage();
	}

	if (hflag) {		/* halftone conversion */
		int y, x;

		memset(g1, 0, sizeof(g1));
		for (y = 0; y < DEF_Y; y++) {
			for (x = 0; x < DEF_X; x++) {
				int graypixloc = y * (DEF_Y) + x;
				int bwpixbyte = y * (DEF_Y/8) + x/8;

				if (g8[graypixloc] > threshold[y%RES][x%RES])
					g1[bwpixbyte] |= 0x80 >> x%8;
			}
		}
	}

	loadimage(dpic, R, (hflag) ? g1 : g8, nr);

	r = Rpt(screen->r.min, addpt(screen->r.min, Pt(DEF_X,DEF_Y)));
	draw(screen, r, dpic, nil, Pt(0,0));

	while(event(&ev) != Ekeyboard)
			;

	exits(0);
}