dhirendvs

Mosaic Effect : Problemof lines in output generated by Pixel Shader

Discussion created by dhirendvs on Dec 20, 2007
Hello,

I have tried out the following Pixel shader code to create a Mosaic
Effect when a texture is applied for a simple rectangle. (Clamp U, V
addressing and Linear Filtering is being used for the texture) :

sampler2D s0 : register( s0 );

float4 mainPS( float2 vTex : TEXCOORD0 ) : COLOR0
{
if( vTex.x < 0.1f )
vTex.x = 0.0f;
else if( vTex.x < 0.2f )
vTex.x = 0.1f;
else if( vTex.x < 0.3f )
vTex.x = 0.2f;
else if( vTex.x < 0.4f )
vTex.x = 0.3f;
else if( vTex.x < 0.5f )
vTex.x = 0.4f;
else if( vTex.x < 0.6f )
vTex.x = 0.5f;
else if( vTex.x < 0.7f )
vTex.x = 0.6f;
else if( vTex.x < 0.8f )
vTex.x = 0.7f;
else if( vTex.x < 0.9f )
vTex.x = 0.8f;
else if( vTex.x < 1.0f )
vTex.x = 0.9f;
else
vTex.x = 1.0f;

if( vTex.y < 0.1f )
vTex.y = 0.0f;
else if( vTex.y < 0.2f )
vTex.y = 0.1f;
else if( vTex.y < 0.3f )
vTex.y = 0.2f;
else if( vTex.y < 0.4f )
vTex.y = 0.3f;
else if( vTex.y < 0.5f )
vTex.y = 0.4f;
else if( vTex.y < 0.6f )
vTex.y = 0.5f;
else if( vTex.y < 0.7f )
vTex.y = 0.6f;
else if( vTex.y < 0.8f )
vTex.y = 0.7f;
else if( vTex.y < 0.9f )
vTex.y = 0.8f;
else if( vTex.y < 1.0f )
vTex.y = 0.9f;
else
vTex.y = 1.0f;

return tex2D( s0, vTex /*- 2.0f*/ );

}

--> The above code could also have been written using :

sampler2D s0 : register( s0 );

float4 mainPS( float2 vTex : TEXCOORD0 ) : COLOR0
{
return tex2D( s0, saturate( floor ( vTex * 10 ) * 0.1 ) /* - 2.0f
*/ );

}

Although the above 2 pixel shaders produce a Mosaic effect, a few
lines having some random color appear along the edges of some
rectangles (These lines can be clearly seen when a complex texture is
applied to the rectangle and "- 2.0f" is uncommented in the last line
in the pixel shader in order to produce a black frame).

The rendering is done using an ATI X700 graphics card. I even tried
disabling mipmaps for the texture and using a texture having
dimensions = some power of 2.But even that didn't solve the problem.

Screen Shots of the output and the original texture are available at
the following link :
http://picasaweb.google.com/dh...OfLinesInMosaicEffect

Can anybody please explain to me how to solve this problem of lines in
the output?

Regards,
Dhiren Sarup.

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