From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from wopr.sciops.net ([216.126.196.60]) by ewsd; Fri Jan 18 12:40:21 EST 2019
Received: (qmail 72893 invoked from network); 18 Jan 2019 09:40:13 -0800
Received: from 105.15.136.77.rev.sfr.net (HELO u25.nope) (qwx@77.136.15.105)
  by wopr.sciops.net with SMTP; 18 Jan 2019 09:40:13 -0800
Message-ID: <29BD3DBBC18C327BB8A22649EADF6E77@wopr.sciops.net>
From: qwx <qwx@sciops.net>
Date: Fri, 18 Jan 2019 18:40:02 +0100
To: 9front@9front.org
Subject: libmemdraw bug?
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"
Content-Transfer-Encoding: 7bit
List-ID: <9front.9front.org>
List-Help: <http://lists.9front.org>
X-Glyph: ➈
X-Bullshit: transactional webscale table dependency WEB2.0 table-scale wrapper 

Hello,

I'm looking at rsc's implementation of pico, which reads in images with
readmemimage().  It only handles 248x248 images, but if extended to
arbitrary dimensions, the images aren't displayed correctly unless their
dimensions don't have the lowest 3 bits set.  In other words, if dx & 7
and/or dy & 7, the image seems to be read/loaded incorrectly.

Pico uses libmemdraw to load and manipulate images, then displays them with
libdraw.  I'm inlining below a simple program that demonstrates the issue.

What is going on?

Thanks,

qwx

/*
; hget http://9front.org/img/ninefront.bit > /tmp/ninefront.bit
; 6c -FTVw test.c && 6l test.6 && 6.out /tmp/ninefront.bit
*/
#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>

void
main(int argc, char **argv)
{
	int fd;
	Memimage *m;
	Image *i;

	if(argc != 2)
		sysfatal("usage");
	if(memimageinit() < 0)
		sysfatal("memimageinit: %r");
	if((fd = open(argv[1], OREAD)) < 0)
		sysfatal("open: %r");
	m = readmemimage(fd);
	close(fd);
	if(m == nil)
		sysfatal("readmemimage: %r");
	if(initdraw(nil, nil, nil) < 0)
		sysfatal("initdraw: %r");
	if((i = allocimage(display, m->r, m->chan, 0, DNofill)) == nil)
		sysfatal("allocimage: %r");
	if(loadimage(i, i->r, byteaddr(m, m->r.min), Dx(m->r)*Dy(m->r)*m->depth/8) < 0)
		sysfatal("loadimage: %r");
	draw(screen, screen->r, i, nil, i->r.min);
	flushimage(display, 1);
	for(;;)
		sleep(1);
}