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/*=========================================================================
Program: Visualization Toolkit
Module: vtkGPUVolumeRayCastMapper_MinIPFourDependentFS.glsl
Copyright (c) Ken Martin, Will Schroeder, Bill Lorensen
All rights reserved.
See Copyright.txt or http://www.kitware.com/Copyright.htm for details.
This software is distributed WITHOUT ANY WARRANTY; without even
the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE. See the above copyright notice for more information.
=========================================================================*/
// Fragment program with ray cast and 4-dependent-component Minimum Intensity
// Projection (MinIP) method.
// Compilation: header part and the projection part are inserted first.
// pos is defined and initialized in header
// rayDir is defined in header and initialized in the projection part
#version 110
uniform sampler3D dataSetTexture;
uniform sampler1D opacityTexture;
uniform vec3 lowBounds;
uniform vec3 highBounds;
// Entry position (global scope)
vec3 pos;
// Incremental vector in texture space (global scope)
vec3 rayDir;
float tMax;
// Sub-functions, depending on cropping mode
float initialMinValue();
vec4 initialColor();
void writeColorAndMinScalar(vec4 color,
vec4 opacity,
float minValue);
void trace(void)
{
// Max intensity is the lowest value.
float minValue=initialMinValue();
vec4 color=initialColor();
bool inside=true;
float t=0.0;
vec4 sample;
bool changed=false;
// We NEED two nested while loops. It is a trick to work around hardware
// limitation about the maximum number of loops.
while(inside)
{
while(inside)
{
sample=texture3D(dataSetTexture,pos);
if(sample.w<minValue)
{
changed=true;
minValue=sample.w;
color=sample;
}
pos=pos+rayDir;
t+=1.0;
// yes, t<tMax && all(greaterThanEqual(pos,lowBounds))
// && all(lessThanEqual(pos,highBounds));
// looks better but the latest nVidia 177.80 has a bug...
inside=t<tMax && pos.x>=lowBounds.x && pos.y>=lowBounds.y
&& pos.z>=lowBounds.z && pos.x<=highBounds.x && pos.y<=highBounds.y
&& pos.z<=highBounds.z;
}
}
if(changed)
{
vec4 opacity=texture1D(opacityTexture,minValue);
writeColorAndMinScalar(color,opacity,minValue);
}
else
{
discard;
}
}
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