Differences in miColor between mental ray 3.4 and 3.5 ?

[dlanier]

Hi,

I have a strange bug that happens only in mental ray 3.5 for Maya 8, the same code works fine for mental ray for Maya 7.

In an output shader, I copy a user frame buffer to a buffer of miColor* then I apply some filters on this buffer.
The user frame buffer copied to the primary frame buffer gives a correct result...
The pseudo code is :

//ClampD is a clamping function.

void ApplyFilter(const miColor* const _inFB, miColor* const _outFB, int FBWidth, int FBHeight)
{
	if &#40;! _inFB || ! _outFB || FBWidth < 0 || FBHeight < 0&#41;
		return;
		
	const miInteger FBWidthMinus1	= FBWidth  - 1;
	const miInteger FBHeightMinus1	= FBHeight - 1;
	
	for &#40;int y=0; y <FBHeight ; ++y&#41; 
	&#123;
		for &#40;int x=0; x<FBWidth; ++x&#41; 
		&#123;
			const int CurPos				= x	+ &#40;y* FBWidth&#41;;
			//Center = x, y
			const miInteger XPixelRight		= ClampD&#40;x + 1, 0, FBWidthMinus1&#41;;
			const miInteger XPixelLeft		= ClampD&#40;x - 1, 0, FBWidthMinus1&#41;;
			const miInteger YPixelUp		= ClampD&#40;y - 1, 0, FBHeightMinus1&#41;;
			const miInteger YPixelDown		= ClampD&#40;y + 1, 0, FBHeightMinus1&#41;;
	
			const miColor& Center			= _inFB&#91;CurPos&#93;;
			const miColor& Right			= _inFB&#91;XPixelRight + &#40;y 			* FBWidth&#41;&#93;;
			const miColor& Left				= _inFB&#91;XPixelLeft  + &#40;y 			* FBWidth&#41;&#93;;
			const miColor& Up				= _inFB&#91;x			+ &#40;YPixelUp		* FBWidth&#41;&#93;;
			const miColor& Down				= _inFB&#91;x			+ &#40;YPixelDown	* FBWidth&#41;&#93;;
			
			_outFB&#91;CurPos&#93;&#46;r				= 4*Center&#46;r - Right&#46;r - Left&#46;r - Up&#46;r - Down&#46;r;
			_outFB&#91;CurPos&#93;&#46;g				= 4*Center&#46;g - Right&#46;g - Left&#46;g - Up&#46;g - Down&#46;g;
			_outFB&#91;CurPos&#93;&#46;b				= 4*Center&#46;b - Right&#46;b - Left&#46;b - Up&#46;b - Down&#46;b;
			
			//Transform in grey level
			miScalar Grey	= &#40;_outFB&#91;CurPos&#93;&#46;r+ _outFB&#91;CurPos&#93;&#46;g+_outFB&#91;CurPos&#93;&#46;b&#41; / 3&#46;0f;
			Grey			= ClampD&#40;Grey,0&#46;f, 1&#46;f&#41;;
			
			_outFB&#91;CurPos&#93;&#46;r = _outFB&#91;CurPos&#93;&#46;g = _outFB&#91;CurPos&#93;&#46;b = Grey;
			_outFB&#91;CurPos&#93;&#46;a = 1&#46;0f;
		&#125;
	&#125;
&#125;

Does anyone see a reason why this would not work with mray for Maya 8 ?
There doesn't seem to have changes in miColor and moreover I am not using any function from mental ray in this code...

Thank you.
Regards,

[dlanier]

I've found that this partly comes from the dither option of the primary frame buffer as my image comes from the primary frame buffer.