[Mesa-dev] [PATCH 2/2] i965/blorp: Add support for blits between SRGB and linear formats.

Paul Berry stereotype441 at gmail.com
Tue Sep 18 14:32:08 PDT 2012 

On 17 September 2012 10:53, Paul Berry <stereotype441 at gmail.com> wrote:

> On 17 September 2012 10:25, Ian Romanick <idr at freedesktop.org> wrote:
>
>> On 09/14/2012 02:56 AM, Paul Berry wrote:
>>
>>> On 11 September 2012 16:24, Kenneth Graunke <kenneth at whitecape.org
>>> <mailto:kenneth at whitecape.org>**> wrote:
>>>
>>>     Fixes colorspace issues in L4D2 when multisampling is enabled (the
>>>     scene was far too dark, but the flashlight area was way too bright).
>>>
>>>     NOTE: This is a candidate for the 9.0 branch.
>>>
>>>     Cc: Paul Berry <stereotype441 at gmail.com
>>>     <mailto:stereotype441 at gmail.**com <stereotype441 at gmail.com>>>
>>>     Signed-off-by: Kenneth Graunke <kenneth at whitecape.org
>>>     <mailto:kenneth at whitecape.org>**>
>>>
>>>
>>>
>>> If I'm reading the spec correctly, it's awfully contradictory.  From GL
>>> 4.3 compatibility profile, section 18.3.1 Blitting Pixel Rectangles:
>>>
>>>      (1) When values are taken from the read buffer, if the value of
>>> FRAMEBUFFER_ATTACHMENT_COLOR_**ENCODING for the framebuffer attachment
>>> corresponding to the read buffer is SRGB (see section 9.2.3), the red,
>>> green, and blue components are converted from the non-linear sRGB color
>>> space according to equation 8.14.
>>>
>>>      (2) When values are taken from the read buffer, no linearization is
>>> performed even if the format of the buffer is SRGB.
>>>
>>>      (3) When values are written to the draw buffers, blit operations
>>> bypass most of the fragment pipeline. The only fragment operations which
>>> affect a blit are the pixel ownership test, the scissor test, and sRGB
>>> conversion (see section 17.3.9). Color, depth, and stencil masks (see
>>> section 17.4.2) are ignored.
>>>
>>
>> A bunch of these language changes are new, and there seem to be some
>> issues.  Basically, sRGB and blits have been horribly broken since the
>> beginning, and fixing it to be sensible is breaking apps.  Wine, for
>> example, is pretty pissed about this.  Note that *none* of the
>> closed-source drivers implement the behavior from the spec.  *None*.
>
>
> Do you know what behaviour is typically implemented or should we go out
> and do some tests?
>

I ran some tests on my system with the nVidia linux binary driver, and
here's what I found:

- Formats GL_RGBA and GL_SRGB8_ALPHA8 are considered "identical" formats
for the purpose of seeing whether an MSAA blit is permitted.
- glBlitFramebuffer() always performs a direct copy (it neither converts to
nor from sRGB space, regardless of the setting of FRAMEBUFFER_SRGB and
regardless of the formats of the source and destination framebuffers).

The test I performed is availble in branch blit-test of git://
github.com/stereotype441/piglit.git.  Simply run "arb_framebuffer_srgb-blit
-auto" and collect standard output.  I'll attach the output I got on my
nVidia system to the end of this email.  Note: at the moment the test
simply outputs a description of how the implementation behaves--it doesn't
do any pass/fail testing.  I'll happily add pass/fail criteria once we
decide what behaviour is "correct".

Considering Ian's comments about sRGB and blits having been "horibly broken
since the beginning", I think what the nVidia driver is doing seems pretty
reasonable (it's simple, it's likely to do what the client application
wants in most cases, and it's consistent with the connotation of "blit"
being a block copy with no image interpretation).  Also, it wouldn't be too
hard to alter the spec to make it match the nVidia driver's behaviour.  All
we would need to do is remove paragraph (1), drop the text "and sRGB
conversion (see section 17.3.9)" from paragraph (3), and alter paragraph
(4) to note that formats that differ only by whether or not they are sRGB
are considered "identical" for purposes of determining whether multisampled
blits are allowed.

I'm interested in hearing if other implementations do the same.  Can
someone (Ken or Anuj perhaps) run my piglit test on an AMD platform and
send out the results?

Assuming we don't see any surprises when we test on AMD, and we decide that
the nVidia behaviour makes sense, then I think Ken's patches are good--they
make Mesa/i965 behave like nVidia in all cases but three:

- scaled blit winsys -> srgb
- scaled blit linear -> srgb
- scaled blit srgb -> srgb

And these three seem to be broken due to a bug in Meta: it only disables
sRGB encoding when blitting with the blitframebuffer_texture() approach.
If it has to fall back to copying the source rectangle into a temporary
texture (which it does when blitting between renderbuffers), then it fails
to disable sRGB encoding.  That seems easily fixable.

Output of "arb_framebuffer_srgb-blit -auto" on my nVidia system follows:

-------------------------
Testing readback in winsys fbo: Direct copy (error=0.000000)
Testing readback in linear fbo: Direct copy (error=0.000000)
Testing readback in srgb fbo: Direct copy (error=0.000000)
Testing readback in linear MSAA fbo: Direct copy (error=0.000000)
Testing readback in srgb MSAA fbo: Direct copy (error=0.000000)
Testing 1:1 blit winsys -> winsys (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit winsys -> winsys (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing 1:1 blit winsys -> winsys (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit winsys -> winsys (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing 1:1 blit winsys -> linear (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit winsys -> linear (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing 1:1 blit winsys -> linear (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit winsys -> linear (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing 1:1 blit winsys -> srgb (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit winsys -> srgb (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing 1:1 blit winsys -> srgb (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit winsys -> srgb (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing 1:1 blit winsys -> linear MSAA (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit winsys -> linear MSAA (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit winsys -> linear MSAA (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit winsys -> linear MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit winsys -> srgb MSAA (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit winsys -> srgb MSAA (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit winsys -> srgb MSAA (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit winsys -> srgb MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit linear -> winsys (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit linear -> winsys (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing 1:1 blit linear -> winsys (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit linear -> winsys (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing 1:1 blit linear -> linear (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit linear -> linear (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing 1:1 blit linear -> linear (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit linear -> linear (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing 1:1 blit linear -> srgb (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit linear -> srgb (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing 1:1 blit linear -> srgb (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit linear -> srgb (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing 1:1 blit linear -> linear MSAA (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit linear -> linear MSAA (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit linear -> linear MSAA (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit linear -> linear MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit linear -> srgb MSAA (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit linear -> srgb MSAA (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit linear -> srgb MSAA (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit linear -> srgb MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit srgb -> winsys (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> winsys (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing 1:1 blit srgb -> winsys (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> winsys (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing 1:1 blit srgb -> linear (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> linear (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing 1:1 blit srgb -> linear (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> linear (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing 1:1 blit srgb -> srgb (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> srgb (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing 1:1 blit srgb -> srgb (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> srgb (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing 1:1 blit srgb -> linear MSAA (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit srgb -> linear MSAA (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit srgb -> linear MSAA (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit srgb -> linear MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit srgb -> srgb MSAA (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> srgb MSAA (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit srgb -> srgb MSAA (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit srgb -> srgb MSAA (FRAMEBUFFER_SRGB enabled): No action
(error=0.000000)
Testing 1:1 blit linear MSAA -> winsys (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit linear MSAA -> winsys (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit linear MSAA -> winsys (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit linear MSAA -> winsys (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit linear MSAA -> linear (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit linear MSAA -> linear (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit linear MSAA -> linear (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit linear MSAA -> linear (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit linear MSAA -> srgb (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit linear MSAA -> srgb (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit linear MSAA -> srgb (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit linear MSAA -> srgb (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit linear MSAA -> linear MSAA (FRAMEBUFFER_SRGB disabled):
Direct copy (error=0.000000)
Testing scaled blit linear MSAA -> linear MSAA (FRAMEBUFFER_SRGB disabled):
No action (error=0.000000)
Testing 1:1 blit linear MSAA -> linear MSAA (FRAMEBUFFER_SRGB enabled):
Direct copy (error=0.000000)
Testing scaled blit linear MSAA -> linear MSAA (FRAMEBUFFER_SRGB enabled):
No action (error=0.000000)
Testing 1:1 blit linear MSAA -> srgb MSAA (FRAMEBUFFER_SRGB disabled):
Direct copy (error=0.000000)
Testing scaled blit linear MSAA -> srgb MSAA (FRAMEBUFFER_SRGB disabled):
No action (error=0.000000)
Testing 1:1 blit linear MSAA -> srgb MSAA (FRAMEBUFFER_SRGB enabled):
Direct copy (error=0.000000)
Testing scaled blit linear MSAA -> srgb MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> winsys (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit srgb MSAA -> winsys (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> winsys (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit srgb MSAA -> winsys (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> linear (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit srgb MSAA -> linear (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> linear (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit srgb MSAA -> linear (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> srgb (FRAMEBUFFER_SRGB disabled): Direct copy
(error=0.000000)
Testing scaled blit srgb MSAA -> srgb (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> srgb (FRAMEBUFFER_SRGB enabled): Direct copy
(error=0.000000)
Testing scaled blit srgb MSAA -> srgb (FRAMEBUFFER_SRGB enabled): No action
(error=0.000000)
Testing 1:1 blit srgb MSAA -> linear MSAA (FRAMEBUFFER_SRGB disabled):
Direct copy (error=0.000000)
Testing scaled blit srgb MSAA -> linear MSAA (FRAMEBUFFER_SRGB disabled):
No action (error=0.000000)
Testing 1:1 blit srgb MSAA -> linear MSAA (FRAMEBUFFER_SRGB enabled):
Direct copy (error=0.000000)
Testing scaled blit srgb MSAA -> linear MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> srgb MSAA (FRAMEBUFFER_SRGB disabled): Direct
copy (error=0.000000)
Testing scaled blit srgb MSAA -> srgb MSAA (FRAMEBUFFER_SRGB disabled): No
action (error=0.000000)
Testing 1:1 blit srgb MSAA -> srgb MSAA (FRAMEBUFFER_SRGB enabled): Direct
copy (error=0.000000)
Testing scaled blit srgb MSAA -> srgb MSAA (FRAMEBUFFER_SRGB enabled): No
action (error=0.000000)
PIGLIT: {'result': 'pass' }
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