Hi everybody

There are many situations were I need to process an array / grid / matrix of pixels in a loop in a post process, mostly for calculating some mean or maximum value or a gradient of a certain set of adjacent pixels. Examples:

• Gaussian blur filter
  
• Calculating mean luminance of a specific area on the screen
  
• Getting pixel nearest to the viewer within a certain range
  
• Checking if at least one pixel of a 2-dimensional array (rectangle) of pixels meets a certain condition
  
• etc.
  

All these applications are typically processed in a 2-dimensional for-loop iterating through the x- and y-axis (rows and columns) of the specified grid, where each iteration makes at least one texture lookup. Therefor they cause heavy GPU load as soon as their dimensions exceed a certain limit, making FPS drop dramatically in many situations.

So, are there strategies to speedup execution times immensely to overcome this limitations? I've already tried these:

1. Either use [loop] or [unroll] attributes
   
2. Use tex2Dlod instead of tex2D in pixel shader
   
3. Wherever possible, make use of these hints: http://msdn.microsoft.com/en-gb/library/windows/desktop/cc627119%28v=vs.85%29.aspx
   

But that's way not enough to make my shaders run well. Are there any better approaches, or maybe some special DX10/11 instructions being of help here?

Thanks for the hints. Unfortunately more than one pass is not an option in my case (engine limitation).

How do I use the hardware linear filter? Do you have an example in HLSL for me?

Urgh, I would have hoped for something like a simple function call like

float3 mean_color = tex2Dlinear(myTextureSampler, uv).rgb

or

sampler2D gSampler =
sampler_state
{
Texture = <gTexture>;
MinFilter = Linear;
MagFilter = Linear;
MipFilter = Linear;
};

So do I have to do this by hand?

Ok, thank you so much!