[Mesa-dev] [Bug 89586] Drivers/DRI/swrast

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=89586

Dan Sebald <daniel.sebald at ieee.org> changed:

           What    |Removed                     |Added
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 Attachment #114342|0                           |1
        is obsolete|                            |

--- Comment #40 from Dan Sebald <daniel.sebald at ieee.org> ---
Created attachment 114710
  --> https://bugs.freedesktop.org/attachment.cgi?id=114710&action=edit
Changeset to fix vertical lines and fine tune positive_unzoom_x() and
negative_unzoom_x()

Attached is an update to the SWRAST legacy changeset.  With this change, the
driver passes all tests in Piglit gl-1.0-pixelzoom check.

The main addition to the changeset over the last changeset is the inclusion of
a tolerance for the ceil() and floor() functions.  The issue is that with
single precision float division and multiplication the formula

(xz - xr) / xfactor

can be off by a fair amount, on the order of 10e-5.  I printed out some numbers
the driver was using in cases there the gl-1.0-pixelzoom alternating-line test
was failing.  The numbers agree exactly with this example result:

octave:3> single(53)/single(400) * single(400)
ans =  52.9999961853027

I put in a tolerance of 0.00004 on the rounding functions.  By my very rough
estimate, I think it is possible to scale input images with dimension of about
100,000 down to typical screen sizes without the added tolerance causing its
own sort of artifact.

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