[Octave-bug-tracker] [bug #44415] OpenGL plotted image has vertical line every 4096 pixels

[Dan Sebald]

Follow-up Comment #11, bug #44415 (project octave):

I'm starting to feel this bug and the tessellation bug are related.  The
answer to this person's question illustrates what is likely the issue:

http://stackoverflow.com/questions/19611745/opengl-black-lines-in-between-tiles?answertab=active#tab-top

In order for OpenGL to generate a pixel value to display on the screen it has
to get that value from what lies in the vicinity of the pixel translated to
the underlying image.  The underlying image and the display can have different
dimensions (i.e., scaling).  To do this OpenGL will do some kind of filtering
which averages surrounding pixels.  In the case of a edge, there is a good
chance OpenGL will use some substitute value--maybe 0xffffff or, hopefully
not, some bogus value pulled from memory--as part of the average.  My guess is
that texture size limits an image section to 4096x4096 pixels.  At edges of
those regions is where the pixel mathematics doesn't work out so nicely.

Why is the line only on the east edge of the region?  I don't know; maybe it's
just at that point the interpolation math works out strange.

The link above talks about supplying pixels around the borders (how that is
done when there is a MAX_TEXTURE_SIZE, I don't know), or perhaps changing the
type of filtering used to generate the on-screen pixels.  I'll investigate
this line of thought a bit.

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