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White border while sampling zoomed textures with directX

Started by arrecio Jul 21, 2012 at 9:30 AM 3 replies 1.6k views

Original Post

Jul 21, 2012 at 9:30 AM

hi,

Im currently porting a work from XNA to DirectX using c++. Im stucked with a texture sampling issue.

There are 3 sprites in the image, original (1:1), XNA sampled (1:1.2) and directX sampled (1:1.2). Im getting a non desired white border in direct X.

Im using LinearClamp in XNA and

Device->SetSamplerState(0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR);
Device->SetSamplerState(0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR);
Device->SetSamplerState(0, D3DSAMP_MIPFILTER, D3DTEXF_LINEAR);
Device->SetSamplerState(0, D3DSAMP_ADDRESSU, D3DTADDRESS_CLAMP);
Device->SetSamplerState(0, D3DSAMP_ADDRESSV, D3DTADDRESS_CLAMP);
Device->SetSamplerState(0, D3DSAMP_ADDRESSW, D3DTADDRESS_CLAMP);

in directX

thnx in advance

[SOLVED]

Seems like XNA content processor sets alpha colors to TransparentBlack, my png has trasnparency over TransparentWhite so the sampler was doing the same but from 2 different sources.

eppo

Jul 21, 2012 at 1:51 PM

I think this article best describes the problem you're dealing with:

http://blogs.msdn.co...ha-cutouts.aspx

When bilinearly filtering, RGB values of texels with zero alpha, even though they are fully transparent, still influence interpolated color values.

As the article recommends, the best thing to counteract this, is to set the color value of these texels to the value of their nearest 'alpha > 0'-texel.

arrecio

Jul 22, 2012 at 8:41 AM

umn I thought I understood it,

So its possible the difference between my XNA code and my dx code results is becouse the content importer in XNA? what is doing some changes on my alpha texels?, in XNA im using content importer and in DX the CreateTextureFromFile method from a png file. Its strange, im taking two different results with (i think) same sampler and blender states on the device. Well thanx eppo, i will work on it.

jrh2365

Jul 22, 2012 at 5:22 PM

I believe the reason you don't see the issue in XNA is because it uses premultiplied alpha by default.

http://blogs.msdn.com/b/shawnhar/archive/2010/04/08/premultiplied-alpha-in-xna-game-studio-4-0.aspx

arrecio

Jul 22, 2012 at 10:38 PM

I believe the reason you don't see the issue in XNA is because it uses premultiplied alpha by default.

http://blogs.msdn.co...studio-4-0.aspx

Yes, by default, but im using this call with SpriteBatch:

SpriteBatch.Begin(SpriteSortMode.Immediate, BlendState.NonPremultiplied, null, null, null, null, matrix);

But u are right, PremultiplyAlpha is turn on for content processor, if i turn off it i get same results, mistery solved.

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