Attachment 57155 Details for Bug 24274 – reorder Bresenham error correction to avoid overshoot.

[patch] reorder Bresenham error correction to avoid overshoot.

0001-fb-reorder-Bresenham-error-correction-to-avoid-overs.patch (text/plain), 2.21 KB, created by Simon Schubert on 2012-02-16 06:28:22 UTC

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Creator: Simon Schubert

Created: 2012-02-16 06:28:22 UTC

Size: 2.21 KB

patch

obsolete

>From 4d4e1e19383c7f7ff85496ffbc9f2c89b231cc78 Mon Sep 17 00:00:00 2001
>From: Simon Schubert <2@0x2c.org>
>Date: Mon, 30 Jan 2012 19:39:03 +0100
>Subject: [PATCH] fb: reorder Bresenham error correction to avoid overshoot.
> #24274
>
>When fbBresSolid draws a line, it can happen that after the last
>pixel, the Bresenham error term overflows, and fbBresSolid paints
>another pixel before adjusting the error term.
>
>However, if this happens on the last pixel (len=0), this extra pixel
>might overshoot the boundary, and, in rare cases, lead to a segfault.
>
>Fix this issue by adjusting for the Bresenham error term before
>drawing the main pixel, not after.
>
>Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=24274
>---
> fb/fbseg.c |   36 ++++++++++++++++++------------------
> 1 files changed, 18 insertions(+), 18 deletions(-)
>
>diff --git a/fb/fbseg.c b/fb/fbseg.c
>index 5a458fe..c05331c 100644
>--- a/fb/fbseg.c
>+++ b/fb/fbseg.c
>@@ -73,6 +73,13 @@ fbBresSolid (DrawablePtr    pDrawable,
> 	bits = 0;
> 	while (len--)
> 	{
>+	    if (e >= 0)
>+	    {
>+		WRITE(dst, FbDoMaskRRop (READ(dst), and, xor, bits));
>+		bits = 0;
>+		dst += dstStride;
>+		e += e3;
>+	    }
> 	    bits |= mask;
> 	    mask = fbBresShiftMask(mask,signdx,dstBpp);
> 	    if (!mask)
>@@ -83,13 +90,6 @@ fbBresSolid (DrawablePtr    pDrawable,
> 		mask = mask0;
> 	    }
> 	    e += e1;
>-	    if (e >= 0)
>-	    {
>-		WRITE(dst, FbDoMaskRRop (READ(dst), and, xor, bits));
>-		bits = 0;
>-		dst += dstStride;
>-		e += e3;
>-	    }
> 	}
> 	if (bits)
> 	    WRITE(dst, FbDoMaskRRop (READ(dst), and, xor, bits));
>@@ -98,19 +98,19 @@ fbBresSolid (DrawablePtr    pDrawable,
>     {
> 	while (len--)
> 	{
>-	    WRITE(dst, FbDoMaskRRop (READ(dst), and, xor, mask));
>+            if (e >= 0)
>+            {
>+                e += e3;
>+                mask = fbBresShiftMask(mask,signdx,dstBpp);
>+                if (!mask)
>+                {
>+                    dst += signdx;
>+                    mask = mask0;
>+                }
>+            }
>+            WRITE(dst, FbDoMaskRRop (READ(dst), and, xor, mask));
> 	    dst += dstStride;
> 	    e += e1;
>-	    if (e >= 0)
>-	    {
>-		e += e3;
>-		mask = fbBresShiftMask(mask,signdx,dstBpp);
>-		if (!mask)
>-		{
>-		    dst += signdx;
>-		    mask = mask0;
>-		}
>-	    }
> 	}
>     }
> 
>-- 
>1.7.9
>

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Attachments on bug 24274: 29995 | 30003 | 30004 | 56113 | 57155 | 59095

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