From 9f880e595c9b6a3bb606339f87ea9c6c2e368671 Mon Sep 17 00:00:00 2001
From: cinap_lenrek <cinap_lenrek@felloff.net>
Date: Tue, 30 Dec 2014 12:44:42 +0100
Subject: [PATCH] libmemdraw: never point Buffer.alpha to nil (thanks mischief)

the boolcopy optimization doesnt doesnt use Buffer.alpha, tho
the debug function dumpbuf() still can dereference it. to keep
it simple, always have Buffer.alpha point to the channel or
&ones when not used.
---
 sys/src/libmemdraw/draw.c | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)

diff --git a/sys/src/libmemdraw/draw.c b/sys/src/libmemdraw/draw.c
index 906949ac7..6ed2a242b 100644
--- a/sys/src/libmemdraw/draw.c
+++ b/sys/src/libmemdraw/draw.c
@@ -405,7 +405,7 @@ struct Buffer {
 	uchar	*red;
 	uchar	*grn;
 	uchar	*blu;
-	uchar	*alpha;
+	uchar	*alpha;	/* is &ones when unused, never nil */
 	uchar	*grey;
 	ulong	*rgba;
 	int	delta;	/* number of bytes to add to pointer to get next pixel to the right */
@@ -1677,7 +1677,7 @@ DBG print("%x\n", w[-1]);
 		b.grey = buf+copyalpha;
 		b.red = b.grn = b.blu = buf+copyalpha;
 		b.delta = copyalpha+1;
-DBG print("alpha %x grey %x\n", b.alpha ? *b.alpha : 0xFF, *b.grey);
+DBG print("alpha %x grey %x\n", *b.alpha, *b.grey);
 	}else{
 		b.blu = buf+copyalpha;
 		b.grn = buf+copyalpha+1;
@@ -1695,7 +1695,7 @@ writebyte(Param *p, uchar *w, Buffer src)
 {
 	Memimage *img;
 	int i, isalpha, isgrey, nb, delta, dx, adelta;
-	uchar ff, *red, *grn, *blu, *grey, *alpha;
+	uchar *red, *grn, *blu, *grey, *alpha;
 	ulong u, mask;
 
 	img = p->img;
@@ -1714,11 +1714,8 @@ writebyte(Param *p, uchar *w, Buffer src)
 	isgrey = img->flags&Fgrey;
 	adelta = src.delta;
 
-	if(isalpha && (alpha == nil || alpha == &ones)){
-		ff = 0xFF;
-		alpha = &ff;
+	if(isalpha && alpha == &ones)
 		adelta = 0;
-	}
 
 	if((img->flags&Fbytes) != 0){
 		int ogry, ored, ogrn, oblu, oalp;
@@ -1829,7 +1826,8 @@ readptr(Param *p, uchar *s, int y)
 	USED(s);
 	q = p->bytermin + y*p->bwidth;
 	b.red = q;	/* ptr to data */
-	b.grn = b.blu = b.grey = b.alpha = nil;
+	b.grn = b.blu = b.grey = nil;
+	b.alpha = &ones;
 	b.rgba = (ulong*)q;
 	b.delta = p->img->depth/8;
 	return b;
@@ -1947,7 +1945,8 @@ genconv(Param *p, uchar *buf, int y)
 	}
 
 	b.red = buf;
-	b.blu = b.grn = b.grey = b.alpha = nil;
+	b.blu = b.grn = b.grey = nil;
+	b.alpha = &ones;
 	b.rgba = (ulong*)buf;
 	b.delta = 0;