<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:Courier New,courier,monaco,monospace,sans-serif;font-size:10pt"><div><span style="font-family: arial,helvetica,sans-serif;">Yes much faster, but with nearest interpolation you obtain ugly result. The problem is the interpolation itself. If you wanna only to have some empty voxels, all you have to do is set the opacity to zero, you don't need to modify the shader. But I need also trilinear interpolation. The result is quite different.</span><br></div><div style="font-family: Courier New,courier,monaco,monospace,sans-serif; font-size: 10pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">Da:</span></b> Tjf (mobile) <tfogal@sci.utah.edu><br><b><span style="font-weight: bold;">A:</span></b> AGPX <agpxnet@yahoo.it><br><b><span
style="font-weight: bold;">Cc:</span></b> vtk vtk <vtkusers@vtk.org>; VTK Developers <vtk-developers@vtk.org>; vtkedge <vtkedge@vtkedge.org><br><b><span style="font-weight: bold;">Inviato:</span></b> Lun 27 dicembre 2010, 21:42:29<br><b><span style="font-weight: bold;">Oggetto:</span></b> Re: [vtk-developers] How to emulate the SetCompositeMethodToClassifyFirst behaviour in hardware (vtkOpenGLGPUVolumeRayCastMapper)...<br></font><br><div>Why would you perform trilinear interpolation manually?</div><div><br></div><div>All you have to do is set two new uniforms -- let's say 'low' and 'high' -- and use gl_nearest interpolation. Then you can:</div><div><br></div><div> If(texture3d(vol) < low) { discard; }</div><div><br></div><div>and likewise for high, in your fragment shader. That's going to be much faster.</div><div><br></div><div>-tom</div><div><br>Am Dec 27, 2010 um 3:19 AM schrieb AGPX <<a rel="nofollow"
ymailto="mailto:agpxnet@yahoo.it" target="_blank" href="mailto:agpxnet@yahoo.it">agpxnet@yahoo.it</a>>:<br><br></div><div></div><blockquote type="cite"><div><div style="font-family: arial,helvetica,sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"><div>Hello everybody,<br><br>I need to render a volume (of scalar values) that have some regions fully transparent. To avoid the problem that arise from trilinear interpolation of the scalars (that show wrong boundary scalars), I have to use the software volume rendering mapper (vtkVolumeRayCastMapper) where you can customize the composite function. In more details, you can invoke the very useful method <span style="font-weight: bold;">SetCompositeMethodToClassifyFirst</span>() of the vtkVolumeRayCastCompositeFunction to obtain the correct result. Unfortunately the software version is slow compared to the hardware one (vtkOpenGLGPUVolumeRayCastMapper). So I have extended the hardware version,
rewriting a GLSL shader (starting from vtkGPUVolumeRayCastMapper_CompositeFS.glsl) in order to
emulate the behaviour of the vtkVolumeRayCastMapper when you invoke the SetCompositeMethodToClassifyFirst() method. The shader is the following (vtkGPUVolumeRayCastMapper_CompositeFS2.glsl) and you have to add it to the vtkOpenGLGPUVolumeRayCastMapper class:<br><font size="2"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">/*=========================================================================</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> Program: Visualization Toolkit</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">
Module: vtkGPUVolumeRayCastMapper_CompositeFS2.glsl</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> All rights reserved.</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span> See Copyright.txt or <a rel="nofollow" target="_blank" href="http://www.kitware.com/Copyright.htm"></a><a rel="nofollow" target="_blank" href="http://www.kitware.com/Copyright.htm">http://www.kitware.com/Copyright.htm</a> for details.</span></span><br
style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> This software is distributed WITHOUT ANY WARRANTY; without even</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> PURPOSE. See the above copyright notice for more information.</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span
style="font-family: Courier New,courier,monaco,monospace,sans-serif;">=========================================================================*/</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">// Fragment program part with ray cast and composite method.</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">#version 110</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform sampler3D dataSetTexture;</span><br
style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform sampler1D opacityTexture;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform vec3 lowBounds;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform vec3 highBounds;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform int textureWidth;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform int
textureHeight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform int textureDepth;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">// Entry position (global scope)</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">vec3 pos;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">// Incremental vector in texture space (global scope)</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;">vec3 rayDir;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">float tMax;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">// from cropping vs no cropping</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">vec4 initialColor();</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;">// from 1 vs 4 component shader.</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">float scalarFromValue(vec4 value);</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">vec4 colorFromValue(vec4 value);</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">// from noshade vs shade.</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">void initShade();</span><br style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">vec4 shade(vec4 value);</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">void trace(void)</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">{</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec4 destColor=initialColor();</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> float remainOpacity=1.0-destColor.a;</span><br
style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> bool inside=true;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> </span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec3 color;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec4 opacity;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"> initShade();</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> </span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> float t=0.0;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> </span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> // We NEED two nested while loops. It is trick to work around hardware</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> //
limitation about the maximum number of loops.</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec3 textureSize = vec3(textureWidth, textureHeight, textureDepth);</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec3 texelSize = vec3(1.0, 1.0, 1.0) / textureSize;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> while(inside)</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> { </span><br style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> while(inside)</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> {<br></span><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec3 texelpos=textureSize*pos;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec3 lerps = fract(texelpos);</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec4 sourcevals[8]; </span><br style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[0] = texture3D(dataSetTexture, pos + vec3(0, 0, 0));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[1] = texture3D(dataSetTexture, pos + vec3(texelSize.x, 0, 0));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[2] = texture3D(dataSetTexture, pos + vec3(0,
texelSize.y, 0));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[3] = texture3D(dataSetTexture, pos + vec3(texelSize.x, texelSize.y, 0));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[4] = texture3D(dataSetTexture, pos + vec3(0, 0, texelSize.z));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[5] = texture3D(dataSetTexture, pos + vec3(texelSize.x,
0, texelSize.z));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[6] = texture3D(dataSetTexture, pos + vec3(0, texelSize.y, texelSize.z));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> sourcevals[7] = texture3D(dataSetTexture, pos + vec3(texelSize.x, texelSize.y, texelSize.z));</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> vec3 m = vec3(1, 1, 1) - lerps;</span><br style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> float weights[8];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> weights[0] = m.x * m.y * m.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> weights[1] = lerps.x * m.y * m.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> weights[2] = m.x * lerps.y * m.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"> weights[3] = lerps.x * lerps.y * m.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> weights[4] = m.x * m.y * lerps.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> weights[5] = lerps.x * m.y * lerps.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> weights[6] = m.x * lerps.y * lerps.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"> weights[7] = lerps.x * lerps.y * lerps.z;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> float weight, totalOpacity;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> totalOpacity = weight = texture1D(opacityTexture,scalarFromValue(sourcevals[0])).a*weights[0];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> color = shade(sourcevals[0]).xyz*weight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"> totalOpacity += weight = texture1D(opacityTexture,scalarFromValue(sourcevals[1])).a*weights[1];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> color += shade(sourcevals[1]).xyz*weight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> totalOpacity += weight = texture1D(opacityTexture,scalarFromValue(sourcevals[2])).a*weights[2];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> color += shade(sourcevals[2]).xyz*weight;</span><br style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> totalOpacity += weight = texture1D(opacityTexture,scalarFromValue(sourcevals[3])).a*weights[3];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> color += shade(sourcevals[3]).xyz*weight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> totalOpacity += weight = texture1D(opacityTexture,scalarFromValue(sourcevals[4])).a*weights[4];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> color +=
shade(sourcevals[4]).xyz*weight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> totalOpacity += weight = texture1D(opacityTexture,scalarFromValue(sourcevals[5])).a*weights[5];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> color += shade(sourcevals[5]).xyz*weight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> totalOpacity += weight = texture1D(opacityTexture,scalarFromValue(sourcevals[6])).a*weights[6];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"> color += shade(sourcevals[6]).xyz*weight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> totalOpacity += weight = texture1D(opacityTexture,scalarFromValue(sourcevals[7])).a*weights[7];</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> color += shade(sourcevals[7]).xyz*weight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> destColor.xyz += remainOpacity*color;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier
New,courier,monaco,monospace,sans-serif;"> remainOpacity *= (1.0 - totalOpacity);</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> pos=pos+rayDir;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> t+=1.0;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> inside=t<tMax && all(greaterThanEqual(pos,lowBounds))</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">
&& all(lessThanEqual(pos,highBounds))</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> && (remainOpacity>=0.0039); // 1/255=0.0039</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> }</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> }</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;"> gl_FragColor = destColor;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family:
Courier New,courier,monaco,monospace,sans-serif;"> gl_FragColor.a = 1.0-remainOpacity;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">}</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">;</span></font><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;">The algorithm performs trilinear interpolation manually so you have to call <span style="font-weight: bold;">SetInterpolationTypeToNearest()</span> when you use this shader. In addition you have 3 new uniform variables:<br><br><font size="2"><span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform int textureWidth;</span><br style="font-family: Courier
New,courier,monaco,monospace,sans-serif;">
<span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform int textureHeight;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;">
<span style="font-family: Courier New,courier,monaco,monospace,sans-serif;">uniform int textureDepth;</span><br style="font-family: Courier New,courier,monaco,monospace,sans-serif;"><br></font>that maintains the dimensions of the 3D texture. You have to modify the class vtkOpenGLGPUVolumeRayCastMapper to provide these additional informations to the shader.<br><br>I hope that this could be helpful for other guys and that (one day) this feature will be added to the VTK library :)<font size="2"><br><br></font>Bye,<br><br>Gianluca Arcidiacono (AGPX)<font size="2"><br></font><br><br></div>
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