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XZ planar image mapping artefact

Started by JimB, May 26, 2008, 06:20:59 AM

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JimB

May 26, 2008, 06:20:59 AM
I watched the Battle of Britain the other night and decided to give an everyday British aerial landscape a pop, while experimenting with multiple resolution image mappings and image based displacement. So far so good except for the top layer image producing a white artefact at the borders (look to the upper right corner, and a line of dots towards the top). The lines also displace, seen when a render is in progress.

I vaguely recall a discussion about camera versus planar projections. Is this the same thing? (sorry, can't find previous discussion)

Projected in the Y, two image maps using border blending to blend one on top of the other. I also tried using the alpha to create the soft border to no avail.
Some bits and bobs
The Galileo Fallacy, 'Argumentum ad Galileus':
"They laughed at Galileo. They're laughing at me. Therefore I am the next Galileo."
Nope. Galileo was right for the simpler reason that he was right.

JimB

#1
May 26, 2008, 06:22:31 AM
The bug in more detail.

Some bits and bobs
The Galileo Fallacy, 'Argumentum ad Galileus':
"They laughed at Galileo. They're laughing at me. Therefore I am the next Galileo."
Nope. Galileo was right for the simpler reason that he was right.

Matt

#2
May 26, 2008, 03:26:28 PM
Can you try disabling unpremultiply in the image map shader?

Matt
Just because milk is white doesn't mean that clouds are made of milk.

JimB

#3
May 26, 2008, 05:33:38 PM
That seems to have fixed it. Thanks Matt.

Weird that it should zing through the clouds. Still, not complaining.  ;)
Some bits and bobs
The Galileo Fallacy, 'Argumentum ad Galileus':
"They laughed at Galileo. They're laughing at me. Therefore I am the next Galileo."
Nope. Galileo was right for the simpler reason that he was right.

rcallicotte

#4
May 26, 2008, 09:11:59 PM
Wow.  That's a cool image.
So this is Disney World.  Can we live here?

Matt

#5
May 26, 2008, 10:05:16 PM
Unpremultiply performs a divide, so if the denominator ramps down to zero it could create surfaces bright enough to be visible through all but the densest of clouds. It is a bug though.

Matt
Just because milk is white doesn't mean that clouds are made of milk.

JimB

#6
May 28, 2008, 01:44:10 AM
@ Calico: Thanks. I see Hurricanes and Spitfires buzzing about...

@ Matt: Read a proper book.  ;)  (I highly recommend The Terror by Dan Simmons - awesome). Is it worth changing the Unpremultiply to unchecked as default in future versions, or swapping over to Premultiply as default?
Some bits and bobs
The Galileo Fallacy, 'Argumentum ad Galileus':
"They laughed at Galileo. They're laughing at me. Therefore I am the next Galileo."
Nope. Galileo was right for the simpler reason that he was right.

Matt

#7
May 28, 2008, 12:00:36 PM
OK Jim, whatever you say ;)

I think I made it unpremultiply by default so that it would work correctly with anti-aliased leaf textures on black backgrounds. If there is no alpha channel in the texture it shouldn't make any difference (I treat this as alpha = 1), but I think I must have got something wrong at the edges of the image. It was a guess, really - pixels that are bright enough to show through clouds strongly suggest a divide by a very small number, as that's the most common way to end up with huge values :)

Matt
Just because milk is white doesn't mean that clouds are made of milk.
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