Re: [Pixman] [Patch] Gradient dithering into pixman (Try 2)

[Marc Jeanmougin]

Hi,

Can I get any input if my second patch follows "the right approach"? Are 
there any astylerc or clang_format to check that my code complies with 
code style ?


Thanks



On 04/19/2018 08:41 PM, Marc Jeanmougin wrote:


Hi,

Could anyone help me from here? If there is still a fundamental 
problem with the patch, I'll be happy to rework it (or if there is 
anything more needed in it)


From what I gathered, pixman is without maintainer, so I'm not sure 
either how to proceed or who to contact...


--

Marc


On 04/08/2018 10:46 PM, Marc Jeanmougin wrote:

Hi, I'm back :)


I tried to implement the proposed changes :

* the gradient walker now deals with argb_t (floats) and not uint32_t
* all gradients are WIDE because of the above change
* WIDE formats (using argb_t) can be dithered on write_back call
depending on the "dither" property of the image (set with
pixman_image_set_dither)
* The dithering is still random. I could try to implement other ones if
it's really needed for the patch to be accepted


Thanks for any feedback, please do tell if there are any more changes
needed for the patch to be accepted.



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Re: [Pixman] [Patch] Gradient dithering into pixman (Try 2)

[Marc Jeanmougin]

Hi,

Could anyone help me from here? If there is still a fundamental problem
with the patch, I'll be happy to rework it (or if there is anything more
needed in it)

From what I gathered, pixman is without maintainer, so I'm not sure
either how to proceed or who to contact...

-- 

Marc


On 04/08/2018 10:46 PM, Marc Jeanmougin wrote:
> Hi, I'm back :)
>
>
> I tried to implement the proposed changes :
>
> * the gradient walker now deals with argb_t (floats) and not uint32_t
> * all gradients are WIDE because of the above change
> * WIDE formats (using argb_t) can be dithered on write_back call
> depending on the "dither" property of the image (set with
> pixman_image_set_dither)
> * The dithering is still random. I could try to implement other ones if
> it's really needed for the patch to be accepted
>
>
> Thanks for any feedback, please do tell if there are any more changes
> needed for the patch to be accepted.
>
>
>
> ___
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> Pixman@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/pixman



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[Pixman] [Patch] Gradient dithering into pixman (Try 2)

[Marc Jeanmougin]

Hi, I'm back :)


I tried to implement the proposed changes :

* the gradient walker now deals with argb_t (floats) and not uint32_t
* all gradients are WIDE because of the above change
* WIDE formats (using argb_t) can be dithered on write_back call
depending on the "dither" property of the image (set with
pixman_image_set_dither)
* The dithering is still random. I could try to implement other ones if
it's really needed for the patch to be accepted


Thanks for any feedback, please do tell if there are any more changes
needed for the patch to be accepted.

-- 
Marc
From 2cd0d0a12c9a68bdedde10ae4b10c335f8961501 Mon Sep 17 00:00:00 2001
From: Marc Jeanmougin 
Date: Sun, 8 Apr 2018 22:25:27 +0200
Subject: [PATCH] Adds a gradient dithering function to pixman.

This dithering is random, resulting is no artifacts and very smooth result,
and uses a very fast prng (xorshift algorithm).

Also adds a pixman_image_set_dithering to toggle the feature,
and a pixman_dither_t type for possible future other implementations.

Signed-off-by: Marc Jeanmougin 
---
 .gitignore   |  2 ++
 pixman/pixman-bits-image.c   | 47 
 pixman/pixman-conical-gradient.c |  7 ++
 pixman/pixman-general.c  |  3 ++-
 pixman/pixman-gradient-walker.c  | 24 +---
 pixman/pixman-image.c| 12 ++
 pixman/pixman-linear-gradient.c  | 11 --
 pixman/pixman-private.h  |  7 +-
 pixman/pixman-radial-gradient.c  | 18 +++
 pixman/pixman-utils.c| 10 +
 pixman/pixman.h  |  9 
 11 files changed, 108 insertions(+), 42 deletions(-)

diff --git a/.gitignore b/.gitignore
index a245b69..02ad685 100644
--- a/.gitignore
+++ b/.gitignore
@@ -53,3 +53,5 @@ test/trap-crasher
 *.ilk
 *.obj
 *.exe
+*.log
+*.trs
diff --git a/pixman/pixman-bits-image.c b/pixman/pixman-bits-image.c
index dcdcc69..bdedb99 100644
--- a/pixman/pixman-bits-image.c
+++ b/pixman/pixman-bits-image.c
@@ -752,6 +752,51 @@ _pixman_bits_image_src_iter_init (pixman_image_t *image, pixman_iter_t *iter)
 iter->get_scanline = _pixman_iter_get_scanline_noop;
 }
 
+
+static float 
+dither_channel (float f, int n_bits, uint32_t *state)
+{
+uint32_t u, i_rem;
+float f_rem;
+if (f>1.0) f = 1.0;
+if (f<0) f = 0.;
+
+u = f * (1 << n_bits);
+u -= (u >> n_bits);
+f_rem = ( (float)(1<common.state);
+pixman_format_code_t format = image->format;
+
+if(image->common.dither == PIXMAN_DITHER_NONE)
+return;
+
+a_size = PIXMAN_FORMAT_A (format);
+r_size = PIXMAN_FORMAT_R (format);
+g_size = PIXMAN_FORMAT_G (format);
+b_size = PIXMAN_FORMAT_B (format);
+
+for (i = 0; i < width; ++i) {
+buf[i].a = dither_channel(buf[i].a, a_size, state);
+buf[i].r = dither_channel(buf[i].r, r_size, state);
+buf[i].g = dither_channel(buf[i].g, g_size, state);
+buf[i].b = dither_channel(buf[i].b, b_size, state);
+}
+}
+
 static uint32_t *
 dest_get_scanline_narrow (pixman_iter_t *iter, const uint32_t *mask)
 {
@@ -856,6 +901,8 @@ dest_write_back_wide (pixman_iter_t *iter)
 int width  = iter->width;
 const uint32_t *buffer = iter->buffer;
 
+dither (image, (argb_t*)buffer, width);
+
 image->store_scanline_float (image, x, y, width, buffer);
 
 if (image->common.alpha_map)
diff --git a/pixman/pixman-conical-gradient.c b/pixman/pixman-conical-gradient.c
index 8bb46ae..35a64f4 100644
--- a/pixman/pixman-conical-gradient.c
+++ b/pixman/pixman-conical-gradient.c
@@ -57,11 +57,11 @@ conical_get_scanline_narrow (pixman_iter_t *iter, const uint32_t *mask)
 int x = iter->x;
 int y = iter->y;
 int width = iter->width;
-uint32_t *buffer = iter->buffer;
+argb_t *buffer = (argb_t*)(iter->buffer);
 
 gradient_t *gradient = (gradient_t *)image;
 conical_gradient_t *conical = (conical_gradient_t *)image;
-uint32_t   *end = buffer + width;
+argb_t   *end = buffer + width;
 pixman_gradient_walker_t walker;
 pixman_bool_t affine = TRUE;
 double cx = 1.;
@@ -165,9 +165,6 @@ conical_get_scanline_wide (pixman_iter_t *iter, const uint32_t *mask)
 {
 uint32_t *buffer = conical_get_scanline_narrow (iter, NULL);
 
-pixman_expand_to_float (
-	(argb_t *)buffer, buffer, PIXMAN_a8r8g8b8, iter->width);
-
 return buffer;
 }
 
diff --git a/pixman/pixman-general.c b/pixman/pixman-general.c
index 6141cb0..809df2c 100644
--- a/pixman/pixman-general.c
+++ b/pixman/pixman-general.c
@@ -141,7 +141,8 @@ 

Re: [Pixman] [patch] Gradient dithering into pixman

[Marc Jeanmougin]

On 03/27/2018 07:45 PM, Bill Spitzak wrote:
> Quick look at the patch and it seems like this will work, though it is a
> random dither. You might get much better compression of .png with a
> patterned dither. I've also had good luck with pseudo-error-diffusion.
> You keep in static memory an accumulated error (per color, but not
> really depending on the location of the pixel) and that is the threshold
> for the random number. This produces a bit more patterning than a
> straight random generator. You might also try it with no random number
> generator at all, but you have to preserve the accumulated error so that
> solid areas that are an integer don't reset it so each adjacent line
> gets the same pattern.

I implemented the accumulated error dithering (attached file, can be
applied over the previous 0001 patch). It greatly improves PNG
compression ratio for purely horizontal gradients (approximately +15%
instead of +1%, in filesize), but produces small artifacts (it's
still way better than no dithering of course, they are almost invisible)
without a random accumulated error at the start of lines (which
increases a lot the filesize).


> May want to call the "on" setting PIXMAN_DITHERING_GOOD. On the
> assumption that anybody who wants it on is happy with "good" dithering,
> and that they may not want to pay for the slowness of "best" dithering.

Considering the prng used, the slowness is almost negligible ("good
except for the small stripes" dithering may in fact be slower)

-- 
Marc
From 85aa2a84e74f3079796ec4686c4fa2acf6c2e93f Mon Sep 17 00:00:00 2001
From: Marc Jeanmougin 
Date: Tue, 27 Mar 2018 21:36:10 +0200
Subject: [PATCH 2/2] Adds PIXMAN_DITHERING_GOOD with diffusion of accumulated
 error

Signed-off-by: Marc Jeanmougin 
---
 pixman/pixman-gradient-walker.c | 21 -
 pixman/pixman-image.c   |  2 +-
 pixman/pixman.h |  1 +
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/pixman/pixman-gradient-walker.c b/pixman/pixman-gradient-walker.c
index dbd7a92..1311fa4 100644
--- a/pixman/pixman-gradient-walker.c
+++ b/pixman/pixman-gradient-walker.c
@@ -52,7 +52,7 @@ _pixman_gradient_walker_init (pixman_gradient_walker_t *walker,
 
 walker->need_reset = TRUE;
 walker->dithering = gradient->dithering;
-walker->prng_state = rand();
+walker->prng_state = (gradient->dithering == PIXMAN_DITHERING_BEST) ? rand() : 0;
 }
 
 static void
@@ -179,6 +179,7 @@ _pixman_dither (pixman_gradient_walker_t *walker, float *in)
 {
 float f_rem = (*in-(float)((int)(*in)));
 uint32_t i_rem = f_rem * 4294967296.;
+uint32_t color_state;
 
 switch (walker->dithering)
 {
@@ -190,6 +191,24 @@ _pixman_dither (pixman_gradient_walker_t *walker, float *in)
 return *in +1;
 else
 return *in;
+
+case PIXMAN_DITHERING_GOOD:
+/* we use prng_state to keep four 8-bit values of errors to propagate */
+color_state = walker->prng_state & 0xff;
+i_rem >>= 24; /*keep 8 most significant bits*/
+color_state+=i_rem;
+if (color_state >= 256){
+color_state -= 256;
+/*rotate*/
+walker->prng_state = (walker->prng_state >> 8) | (color_state<<24);
+return *in+1;
+}
+else {
+/*rotate*/
+walker->prng_state = (walker->prng_state >> 8) | (color_state<<24);
+return *in;
+}
+
 case PIXMAN_DITHERING_NONE:
 default:
 /* round */
diff --git a/pixman/pixman-image.c b/pixman/pixman-image.c
index 75f168e..61e6988 100644
--- a/pixman/pixman-image.c
+++ b/pixman/pixman-image.c
@@ -102,7 +102,7 @@ _pixman_init_gradient (gradient_t *  gradient,
 gradient->n_stops = n_stops;
 
 gradient->common.property_changed = gradient_property_changed;
-gradient->dithering = PIXMAN_DITHERING_NONE;
+gradient->dithering = PIXMAN_DITHERING_GOOD;
 
 return TRUE;
 }
diff --git a/pixman/pixman.h b/pixman/pixman.h
index 5ac0db6..2422eb8 100644
--- a/pixman/pixman.h
+++ b/pixman/pixman.h
@@ -319,6 +319,7 @@ typedef enum
 typedef enum
 {
 PIXMAN_DITHERING_NONE,
+PIXMAN_DITHERING_GOOD,
 PIXMAN_DITHERING_BEST
 } pixman_dithering_t;
 
-- 
2.16.2



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Re: [Pixman] [patch] Gradient dithering into pixman

[Bill Spitzak]

I get it, the dithering is turned on/off with a Cairo control. I thought
you were suggesting that it is turned off if the destination is an image.

Quick look at the patch and it seems like this will work, though it is a
random dither. You might get much better compression of .png with a
patterned dither. I've also had good luck with pseudo-error-diffusion. You
keep in static memory an accumulated error (per color, but not really
depending on the location of the pixel) and that is the threshold for the
random number. This produces a bit more patterning than a straight random
generator. You might also try it with no random number generator at all,
but you have to preserve the accumulated error so that solid areas that are
an integer don't reset it so each adjacent line gets the same pattern.

May want to call the "on" setting PIXMAN_DITHERING_GOOD. On the assumption
that anybody who wants it on is happy with "good" dithering, and that they
may not want to pay for the slowness of "best" dithering.


On Tue, Mar 27, 2018 at 2:20 AM, Marc Jeanmougin  wrote:

> Hi,
>
> Le 27/03/2018 à 02:04, Søren Sandmann a écrit :
> > A long time ago I wrote this:
> >
> > https://lists.freedesktop.org/archives/pixman/2012-July/002175.html
> >
> > about how dithering could be added to pixman. The basic idea is that
> > "dithering" is a property of the destination image, not of the
> > gradient.  I still think this is the right way to do it.
>
> Thank you for your input. Would it be possible to use your preferred way
> of doing it to my patch ?
>
> Le 27/03/2018 à 03:47, Bill Spitzak a écrit :
> > I don't understand why you would want to disable it when writing .png
> > files. There will be banding in the .png file, which I would think is
> > worse than the increased size.
> Depends. In many cases there is no visible banding, and some people may
> not want a x100 filesize increase for it (for files that are entirely
> made of gradients).
>
> > Also kind of fools the user if they did not look at the .png file and
> > only at InkScape's display.
> We already have such differences for filter quality, and of course it
> would be possible to switch it in the display windows for previewing.
>
> --
> Marc
>
>
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Re: [Pixman] [patch] Gradient dithering into pixman

[Marc Jeanmougin]

Hi,

Le 27/03/2018 à 02:04, Søren Sandmann a écrit :
> A long time ago I wrote this:
>
>     https://lists.freedesktop.org/archives/pixman/2012-July/002175.html
>
> about how dithering could be added to pixman. The basic idea is that
> "dithering" is a property of the destination image, not of the
> gradient.  I still think this is the right way to do it.

Thank you for your input. Would it be possible to use your preferred way
of doing it to my patch ?

Le 27/03/2018 à 03:47, Bill Spitzak a écrit :
> I don't understand why you would want to disable it when writing .png
> files. There will be banding in the .png file, which I would think is
> worse than the increased size.
Depends. In many cases there is no visible banding, and some people may
not want a x100 filesize increase for it (for files that are entirely
made of gradients).

> Also kind of fools the user if they did not look at the .png file and
> only at InkScape's display.
We already have such differences for filter quality, and of course it
would be possible to switch it in the display windows for previewing.

-- 
Marc

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Re: [Pixman] [patch] Gradient dithering into pixman

[Bill Spitzak]

I don't understand why you would want to disable it when writing .png
files. There will be banding in the .png file, which I would think is worse
than the increased size. Also kind of fools the user if they did not look
at the .png file and only at InkScape's display.


On Mon, Mar 26, 2018 at 5:04 PM, Søren Sandmann 
wrote:

> Hi,
>
> A long time ago I wrote this:
>
> https://lists.freedesktop.org/archives/pixman/2012-July/002175.html
>
> about how dithering could be added to pixman. The basic idea is that
> "dithering" is a property of the destination image, not of the gradient.  I
> still think this is the right way to do it.
>
>
> Søren
>
> On Mon, Mar 26, 2018 at 6:37 PM, Marc Jeanmougin 
> wrote:
>
>> Hi,
>>
>> I'm Marc, I'm an Inkscape contributor, and I would like to improve
>> pixman by providing a patch to allow gradient dithering, to eliminate
>> all gradient banding. This "banding" problem is hugely visible in many
>> Inkscape files, and I hope you could help me putting it into pixman,
>> then in exposing the functionality into cairo.
>>
>> I tried to very closely follow the existing code style, and I came up
>> with the proof of concept (attached Proof_of_concept.patch ), which
>> applies to pixman/master to enable the feature directly.
>>
>> Since Inkscape also uses pixman to render files when exporting to png,
>> and that kind of dithering affects very significantly the file size (PNG
>> compression algorithm and randomness don't mix well) we also need a
>> switch to enable/disable it "at will".
>>
>> I tried to understand how it could be done by looking at
>> pixman_image_set_* functions and finally came up with the other patch
>> attached 0001-Adds-a-gradient-dithering-function-to-pixman.patch (which
>> cannot directly be tested, since it would require changes in cairo to
>> call pixman_image_set_dithering, but changing "gradient->dithering =
>> PIXMAN_DITHERING_NONE;" to _BEST in pixman-image.c works)
>>
>> Thanks for any help in merging this, or any pointer to how to improve it,
>>
>> --
>> Marc
>>
>> ___
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>> https://lists.freedesktop.org/mailman/listinfo/pixman
>>
>>
>
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Re: [Pixman] [patch] Gradient dithering into pixman

[Søren Sandmann]

Hi,

A long time ago I wrote this:

https://lists.freedesktop.org/archives/pixman/2012-July/002175.html

about how dithering could be added to pixman. The basic idea is that
"dithering" is a property of the destination image, not of the gradient.  I
still think this is the right way to do it.


Søren

On Mon, Mar 26, 2018 at 6:37 PM, Marc Jeanmougin  wrote:

> Hi,
>
> I'm Marc, I'm an Inkscape contributor, and I would like to improve
> pixman by providing a patch to allow gradient dithering, to eliminate
> all gradient banding. This "banding" problem is hugely visible in many
> Inkscape files, and I hope you could help me putting it into pixman,
> then in exposing the functionality into cairo.
>
> I tried to very closely follow the existing code style, and I came up
> with the proof of concept (attached Proof_of_concept.patch ), which
> applies to pixman/master to enable the feature directly.
>
> Since Inkscape also uses pixman to render files when exporting to png,
> and that kind of dithering affects very significantly the file size (PNG
> compression algorithm and randomness don't mix well) we also need a
> switch to enable/disable it "at will".
>
> I tried to understand how it could be done by looking at
> pixman_image_set_* functions and finally came up with the other patch
> attached 0001-Adds-a-gradient-dithering-function-to-pixman.patch (which
> cannot directly be tested, since it would require changes in cairo to
> call pixman_image_set_dithering, but changing "gradient->dithering =
> PIXMAN_DITHERING_NONE;" to _BEST in pixman-image.c works)
>
> Thanks for any help in merging this, or any pointer to how to improve it,
>
> --
> Marc
>
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[Pixman] [patch] Gradient dithering into pixman

[Marc Jeanmougin]

Hi,

I'm Marc, I'm an Inkscape contributor, and I would like to improve
pixman by providing a patch to allow gradient dithering, to eliminate
all gradient banding. This "banding" problem is hugely visible in many
Inkscape files, and I hope you could help me putting it into pixman,
then in exposing the functionality into cairo.

I tried to very closely follow the existing code style, and I came up
with the proof of concept (attached Proof_of_concept.patch ), which
applies to pixman/master to enable the feature directly.

Since Inkscape also uses pixman to render files when exporting to png,
and that kind of dithering affects very significantly the file size (PNG
compression algorithm and randomness don't mix well) we also need a
switch to enable/disable it "at will".

I tried to understand how it could be done by looking at
pixman_image_set_* functions and finally came up with the other patch
attached 0001-Adds-a-gradient-dithering-function-to-pixman.patch (which
cannot directly be tested, since it would require changes in cairo to
call pixman_image_set_dithering, but changing "gradient->dithering =
PIXMAN_DITHERING_NONE;" to _BEST in pixman-image.c works)

Thanks for any help in merging this, or any pointer to how to improve it,

-- 
Marc
diff --git a/pixman/pixman-gradient-walker.c b/pixman/pixman-gradient-walker.c
index 822f8e6..c0fbebb 100644
--- a/pixman/pixman-gradient-walker.c
+++ b/pixman/pixman-gradient-walker.c
@@ -27,6 +27,9 @@
 #include 
 #endif
 #include "pixman-private.h"
+#include 
+#include 
+#include 
 
 void
 _pixman_gradient_walker_init (pixman_gradient_walker_t *walker,
@@ -48,6 +51,8 @@ _pixman_gradient_walker_init (pixman_gradient_walker_t *walker,
 walker->repeat= repeat;
 
 walker->need_reset = TRUE;
+walker->dithering = PIXMAN_DITHERING_BEST;
+walker->prng_state = rand();
 }
 
 static void
@@ -169,6 +174,42 @@ gradient_walker_reset (pixman_gradient_walker_t *walker,
 walker->need_reset = FALSE;
 }
 
+static inline uint8_t
+_pixman_dither (pixman_gradient_walker_t *walker, float *in)
+{
+float f_rem = (*in-(float)((int)(*in)));
+uint32_t i_rem = f_rem * 4294967296.;
+
+switch (walker->dithering)
+{
+case PIXMAN_DITHERING_NONE:
+/* round */
+return *in + 0.5f;
+case PIXMAN_DITHERING_GOOD:
+/* only dither between 1/4 and 3/4 */
+if (f_rem < 0.25 || f_rem >= 0.75)
+return *in + 0.5f;
+else 
+i_rem += (i_rem - (1<<31));
+break;
+/*case PIXMAN_DITHERING_EDGES:
+if (f_rem < 0.48 || f_rem >= 0.52)
+return *in + 0.5f;
+else
+i_rem += (24*(((int)i_rem) - (1<<31)));
+break;*/
+case PIXMAN_DITHERING_BEST:
+break;
+}
+/* we want a8 = a with probability (1-(a-int(a))) and
+ * a8=a+1 with probability a-int(a)
+ */
+if ((walker->prng_state = pixman_prng_get(walker->prng_state)) < i_rem)
+return *in +1;
+else
+return *in;
+}
+
 uint32_t
 _pixman_gradient_walker_pixel (pixman_gradient_walker_t *walker,
pixman_fixed_48_16_t  x)
@@ -188,10 +229,10 @@ _pixman_gradient_walker_pixel (pixman_gradient_walker_t *walker,
 g = a * (walker->g_s * y + walker->g_b);
 b = a * (walker->b_s * y + walker->b_b);
 
-a8 = a + 0.5f;
-r8 = r + 0.5f;
-g8 = g + 0.5f;
-b8 = b + 0.5f;
+a8 = _pixman_dither(walker, );
+r8 = _pixman_dither(walker, );
+g8 = _pixman_dither(walker, );
+b8 = _pixman_dither(walker, );
 
 v = ((a8 << 24) & 0xff00) |
 ((r8 << 16) & 0x00ff) |
diff --git a/pixman/pixman-linear-gradient.c b/pixman/pixman-linear-gradient.c
index 40c8c9f..5ad6f45 100644
--- a/pixman/pixman-linear-gradient.c
+++ b/pixman/pixman-linear-gradient.c
@@ -160,11 +160,8 @@ linear_get_scanline_narrow (pixman_iter_t  *iter,
 
 	if (((pixman_fixed_32_32_t )(inc * width)) == 0)
 	{
-	register uint32_t color;
-
-	color = _pixman_gradient_walker_pixel (, t);
 	while (buffer < end)
-		*buffer++ = color;
+		*buffer++ = _pixman_gradient_walker_pixel (, t);
 	}
 	else
 	{
@@ -236,6 +233,7 @@ linear_get_scanline_wide (pixman_iter_t *iter, const uint32_t *mask)
 void
 _pixman_linear_gradient_iter_init (pixman_image_t *image, pixman_iter_t  *iter)
 {
+/*
 if (linear_gradient_is_horizontal (
 	iter->image, iter->x, iter->y, iter->width, iter->height))
 {
@@ -246,7 +244,7 @@ _pixman_linear_gradient_iter_init (pixman_image_t *image, pixman_iter_t  *iter)
 
 	iter->get_scanline = _pixman_iter_get_scanline_noop;
 }
-else
+else*/
 {
 	if (iter->iter_flags & ITER_NARROW)
 	iter->get_scanline = linear_get_scanline_narrow;
diff --git a/pixman/pixman-private.h b/pixman/pixman-private.h
index 73a5414..a3e026a 100644
--- a/pixman/pixman-private.h
+++ b/pixman/pixman-private.h
@@ -352,6 +352,9 @@ typedef struct
 pixman_repeat_t	repeat;
 
 pixman_bool_t