From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mx.sdf.org ([205.166.94.24]) by ewsd; Fri Oct 30 13:45:15 -0400 2020
Received: from sdf.org (IDENT:nicolagi@otaku.sdf.org [205.166.94.8])
	by mx.sdf.org (8.15.2/8.14.5) with ESMTPS id 09UHjCSQ010311
	(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits) verified NO)
	for <9front@9front.org>; Fri, 30 Oct 2020 17:45:12 GMT
Received: (from nicolagi@localhost)
	by sdf.org (8.15.2/8.12.8/Submit) id 09UHjBeD007649
	for 9front@9front.org; Fri, 30 Oct 2020 17:45:11 GMT
Message-ID: <012440E4E4FD8FD9B1E1955DA8640092@sdf.org>
To: 9front@9front.org
Subject: truetypefs
Date: Fri, 30 Oct 2020 17:45:07 +0000
From: nicolagi@sdf.org
MIME-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-MIME-Autoconverted: from 8bit to quoted-printable by mx.sdf.org id 09UHjCSQ010311
List-ID: <9front.9front.org>
List-Help: <http://lists.9front.org>
X-Glyph: ➈
X-Bullshit: compliant ISO-certified storage-oriented package-scale singleton NoSQL locator 

Hi all,

truetypefs used to crash for me; it used to happen when trying to display
some non-ASCII glyph, e.g., an accented vowel: =C3=A0.

Commenting out the assertion at /sys/src/libttf/scan.c:371 solves the
problem for me, although I fail to grasp why, and whether it's the
right fix; I'll share why I gleaned so far.

(Since text renders correctly on my end, I presume the assertion is
wrong, but it's really just a guess.)

The flags field of TTPoint defined at
/sys/include/ttf.h:/^struct.TTPoint/ seems to hold values defined at
/sys/src/libttf/impl.h:/ONCURVE/.  So in other words, the assertion I
commented out fails because a point is expected to be on the curve,
while it is not.  What point is it?  If I were to guess from
/sys/src/libttf/scan.c:370, I'd say the final point of each countour.

AFAICS, the only place that can clear the bit is
/sys/src/libttf/hint.c:1377, part of some hinting operation (flip
range).  Is the operation wrong, or is the assertion wrong?

I'm including a patch that replaces magic numbers with enum values and
comments out the problematic assertion.  I realize it's not of much
value but I hope someone can improve on it.

Thanks,

Nicola

diff -r f4aa654bc414 sys/include/ttf.h
--- a/sys/include/ttf.h	Thu Oct 29 18:26:35 2020 +0100
+++ b/sys/include/ttf.h	Fri Oct 30 17:33:50 2020 +0000
@@ -31,6 +31,7 @@
 };
 struct TTPoint {
 	int x, y;
+	/* ONCURVE, TOUCHX, TOUCHY, TOUCH. */
 	u8int flags;
 };
 struct TTBitmap {
diff -r f4aa654bc414 sys/src/libttf/glyf.c
--- a/sys/src/libttf/glyf.c	Thu Oct 29 18:26:35 2020 +0100
+++ b/sys/src/libttf/glyf.c	Fri Oct 30 17:33:50 2020 +0000
@@ -135,7 +135,7 @@
 		goto err;
 	for(i =3D 0; i < np; i++){
 		p =3D &g->pt[g->npt + i];
-		p->flags =3D *fp & 1;
+		p->flags =3D *fp & ONCURVE;
 		switch(*fp++ & 0x12){
 		case 0x00: ttfunpack(f, "w", &temp16); p->x =3D lastx +=3D temp16; bre=
ak;
 		case 0x02: ttfunpack(f, "b", &temp8); p->x =3D lastx -=3D temp8; break=
;
diff -r f4aa654bc414 sys/src/libttf/hint.c
--- a/sys/src/libttf/hint.c	Thu Oct 29 18:26:35 2020 +0100
+++ b/sys/src/libttf/hint.c	Fri Oct 30 17:33:50 2020 +0000
@@ -136,8 +136,8 @@
 	if((n & RP2) !=3D 0)
 		pi =3D h->f->rp[(n >> 4 & 3) - 1];
 	if((n & NOTOUCH) =3D=3D 0){
-		if(h->f->fvx !=3D 0) p.flags |=3D 2;
-		if(h->f->fvy !=3D 0) p.flags |=3D 4;
+		if(h->f->fvx !=3D 0) p.flags |=3D TOUCHX;
+		if(h->f->fvy !=3D 0) p.flags |=3D TOUCHY;
 	}
 	if((h->f->zp >> (n >> 8 & 3) & 1) !=3D 0){
 		if(h->g =3D=3D nil)
@@ -1374,7 +1374,7 @@
 		herror(h, "FLIPRG without glyph");
 	for(; i <=3D e; i++)
 		if((int)i < h->g->npt)
-			h->g->pt[i].flags =3D h->g->pt[i].flags & ~1 | h->ip[-1] & 1;
+			h->g->pt[i].flags =3D h->g->pt[i].flags & ~ONCURVE | h->ip[-1] & 1;
 }
=20
 static void
diff -r f4aa654bc414 sys/src/libttf/scan.c
--- a/sys/src/libttf/scan.c	Thu Oct 29 18:26:35 2020 +0100
+++ b/sys/src/libttf/scan.c	Fri Oct 30 17:33:50 2020 +0000
@@ -368,9 +368,9 @@
 	for(i =3D 0; i < g->ncon; i++){
 		if(g->confst[i] + 1 >=3D g->confst[i+1]) continue;
 		p =3D g->pt[g->confst[i]];
-		assert((p.flags & 1) !=3D 0);
+		/* assert((p.flags & ONCURVE) !=3D 0); */
 		for(j =3D g->confst[i]; j++ < g->confst[i+1]; ){
-			if(j < g->confst[i+1] && (g->pt[j].flags & 1) =3D=3D 0)
+			if(j < g->confst[i+1] && (g->pt[j].flags & ONCURVE) =3D=3D 0)
 				q =3D g->pt[j++];
 			else
 				q =3D p;
@@ -378,14 +378,14 @@
 				r =3D g->pt[g->confst[i]];
 			else{
 				r =3D g->pt[j];
-				if((g->pt[j].flags & 1) =3D=3D 0){
+				if((g->pt[j].flags & ONCURVE) =3D=3D 0){
 					r.x =3D (r.x + q.x) / 2;
 					r.y =3D (r.y + q.y) / 2;
 				}
 			}
 			dobezier(&s, p, q, r);
 			p =3D r;
-			if(j < g->confst[i+1] && (g->pt[j].flags & 1) =3D=3D 0)
+			if(j < g->confst[i+1] && (g->pt[j].flags & ONCURVE) =3D=3D 0)
 				j--;
 		}
 	}
@@ -440,9 +440,9 @@
 		(*fp)[0] =3D p.x * scale;
 		(*fp)[1] =3D p.y * scale + offy;
 	}
-	assert((p.flags & 1) !=3D 0);
+	assert((p.flags & ONCURVE) !=3D 0);
 	for(j =3D g->confst[i]; j++ < g->confst[i+1]; ){
-		if(j < g->confst[i+1] && (g->pt[j].flags & 1) =3D=3D 0)
+		if(j < g->confst[i+1] && (g->pt[j].flags & ONCURVE) =3D=3D 0)
 			q =3D g->pt[j++];
 		else
 			q =3D p;
@@ -450,7 +450,7 @@
 			r =3D g->pt[g->confst[i]];
 		else{
 			r =3D g->pt[j];
-			if((g->pt[j].flags & 1) =3D=3D 0){
+			if((g->pt[j].flags & ONCURVE) =3D=3D 0){
 				r.x =3D (r.x + q.x) / 2;
 				r.y =3D (r.y + q.y) / 2;
 			}
@@ -469,7 +469,7 @@
 		}
 		p =3D r;
 		n +=3D 2;
-		if(j < g->confst[i+1] && (g->pt[j].flags & 1) =3D=3D 0)
+		if(j < g->confst[i+1] && (g->pt[j].flags & ONCURVE) =3D=3D 0)
 			j--;
 	}
 	if(np !=3D nil)