[libGD] #230 [Task opened] Test gdimageline_aa fails for gdimageline_aa_d_*_exp.png

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User who did this - Jim DeLaHunt (JimDeLaHunt) 

Attached to Project - libGD
Summary - Test gdimageline_aa fails for gdimageline_aa_d_*_exp.png
Task Type - Bug Report
Category - Drawing function
Status - Unconfirmed
Assigned To - 
Operating System - Other
Severity - Low
Priority - Normal
Reported Version - 2.0.35
Due in Version - Undecided
Due Date - Undecided
Details - I built gd 2.0.35 and ran the built-in tests on my machine. All tests passed except for gdimageline_aa.  This test exercises anti-aliased line drawing, generating eight different images and comparing them to references supplied with gd.  Two of those eight failed.  

How to reproduce bug:
* Unarchive gd 2.0.35 source code on a Mac OS X 10.5.8 machine using the default compiler (I think /usr/bin/gcc).
* cmake, make all, make install as needed.
* ctest . to run all the tests.

Observed behaviour:
* Output from ctest . is:
<code>The following tests FAILED:
	  5 - gdimageline_aa (Failed)
</code>
* In root of project directory, the following files appear (attached):
gdimageline_aa.c_38_diff.png	gdimageline_aa.c_41_diff.png
gdimageline_aa.c_38_out.png	gdimageline_aa.c_41_out.png

The *_out.png files appear to be the images generated by the test code, and the *_diff.png files appear to be images containing differences between the test output and the reference.   These files are attached.

Expected behaviour:
* All tests pass.

Looking at the *_diff.png files, it appears that the left end of the diagonal lines are lower (larger +y coordinate) in the test output than in the reference.

To check this, I patched tests/gdimageline/gdimageline_aa.c to print out the parameters it uses to draw the diagonal line, when a test case fails. Patch is attached.  Here's the output I received when running the test standalone (paths and line wraps edited):

<code>% ./tests/gdimageline/gdimageline_aa
..../tests/gdimageline/gdimageline_aa_a_0_exp.png draws line from -10,-49 to 20,100.
   Width: 10, height 100, idx 0, reverse_x 1, gradient 5.000000, offset 0.
..../tests/gdimageline/gdimageline_aa_a_1_exp.png draws line from -10,0 to 20,150.
   Width: 10, height 100, idx 1, reverse_x 1, gradient 5.000000, offset 10.
..../tests/gdimageline/gdimageline_aa_b_0_exp.png draws line from 10,50 to -20,200.
   Width: 10, height 100, idx 2, reverse_x -1, gradient 5.000000, offset 20.
..../tests/gdimageline/gdimageline_aa_b_1_exp.png draws line from 10,0 to -20,150.
   Width: 10, height 100, idx 1, reverse_x -1, gradient 5.000000, offset 10.
..../tests/gdimageline/gdimageline_aa_c_0_exp.png draws line from -100,-4 to 200,10.
   Width: 100, height 10, idx 0, reverse_x 1, gradient 0.050000, offset 0.
..../tests/gdimageline/gdimageline_aa_c_1_exp.png draws line from -100,0 to 200,15.
   Width: 100, height 10, idx 1, reverse_x 1, gradient 0.050000, offset 100.
..../tests/gdimageline/gdimageline_aa_d_0_exp.png draws line from 100,5 to -200,20.
   Width: 100, height 10, idx 2, reverse_x -1, gradient 0.050000, offset 200.
..../tests/gdimageline/gdimageline_aa_d_0_exp.png failed
..../tests/gdimageline/gdimageline_aa_d_1_exp.png draws line from 100,0 to -200,15.
   Width: 100, height 10, idx 1, reverse_x -1, gradient 0.050000, offset 100.
..../tests/gdimageline/gdimageline_aa_d_1_exp.png failed
</code>

Does anyone else using gcc on a Mac OS X 10.5.8 OS get this test to pass when first compiled?

The test case per se is low severity, because it's no big deal to a user if a test case fails. However, if it points to some variance in gd behaviour, then that variance could cause a more severe bug in the field.

More information can be found at the following URL:
http://bugs.libgd.org/?do=details&task_id=230

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