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//=========================================================================
//
// Program: Visualization Toolkit
// Module: vtkStructuredGridLIC2D_fs.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.
//
//=========================================================================
// Filename: vtkStructuredGridLIC2D_fs.glsl
// Filename is useful when using gldb-gui
#version 120 // because of transpose()
/*
For an input structure grid, this computes the inverse jacobian for each point.
Algorithm:
* PASS ONE
* * render to compute the transformed vector field for the points.
* PASS TWO
* * perform LIC with the new vector field. This has to happen in a different
* pass than computation of the transformed vector.
* PASS THREE
* * Render structued slice quads with correct texture correct tcoords and apply
* the LIC texture to it.
*/
uniform sampler2D texPoints; // point coordinates
uniform sampler2D texVectorField; // vector field.
uniform vec3 uDimensions; // structured dimensions; initially == (width, height, 1)
uniform int uSlice; // 0,1,2
ivec3 getIJK(vec3 ninjnk, vec3 dims)
{
return ivec3(floor(ninjnk*(dims-1.0)+vec3(0.5, 0.5, 0.5)));
}
vec3 getVector(ivec3 ijk, vec3 dims, sampler2D field)
{
// ignoring k component for now since dims = (width, height, 1)
// not any more.
vec3 rcoord = vec3(ijk)/max(vec3(1.0), dims-1.0);
vec2 tcoord;
if(uSlice==0)
{
tcoord.xy=rcoord.yz;
}
else
{
if(uSlice==1)
{
tcoord.xy=rcoord.xz;
}
else
{
tcoord.xy=rcoord.xy;
}
}
return texture2D(field, tcoord).xyz;
}
float determinant(mat3 m)
{
// develop determinant along first row.
return m[0][0]*(m[2][2]*m[1][1] - m[2][1]*m[1][2])
- m[1][0]*(m[2][2]*m[0][1] - m[2][1]*m[0][2])
+ m[2][0]*(m[1][2]*m[0][1] - m[1][1]*m[0][2]);
}
mat3 inverse(mat3 mm, float det)
{
mat3 m=transpose(mm);
mat3 adjM = mat3(
m[2][2]*m[1][1]-m[2][1]*m[1][2], -(m[2][2]*m[0][1]-m[2][1]*m[0][2]), m[1][2]*m[0][1]-m[1][1]*m[0][2],
-(m[2][2]*m[1][0]-m[2][0]*m[1][2]), m[2][2]*m[0][0]-m[2][0]*m[0][2], -(m[1][2]*m[0][0]-m[1][0]*m[0][2]),
m[2][1]*m[1][0]-m[2][0]*m[1][1], -(m[2][1]*m[0][0]-m[2][0]*m[0][1]), m[1][1]*m[0][0]-m[1][0]*m[0][1]
);
return adjM/det;
}
mat3 jacobian(ivec3 ijk, vec3 dims, sampler2D tex)
{
// Jacobian is estimated with a central finite difference technique.
// get point coordinates at (i, j, k),
// vec3 pts_I_J_K = getVector(ijk, dims, tex);
//(i-1, j, k), (i+1, j, k)
vec3 pts_IM1_J_K = getVector(ivec3(ijk.x-1, ijk.yz), dims, tex);
vec3 pts_I1_J_K = getVector(ivec3(ijk.x+1, ijk.yz), dims, tex);
// (i, j-1, k), (i, j+1, k)
vec3 pts_I_JM1_K = getVector(ivec3(ijk.x, ijk.y-1, ijk.z), dims, tex);
vec3 pts_I_J1_K = getVector(ivec3(ijk.x, ijk.y+1, ijk.z), dims, tex);
// (i, j, k-1), (i, j, k+1).
vec3 pts_I_J_KM1 = getVector(ivec3(ijk.xy, ijk.z-1), dims, tex);
vec3 pts_I_J_K1 = getVector(ivec3(ijk.xy, ijk.z+1), dims, tex);
vec3 col1 = 0.5*(pts_I1_J_K - pts_IM1_J_K);
vec3 col2 = 0.5*(pts_I_J1_K - pts_I_JM1_K);
vec3 col3 = 0.5*(pts_I_J_K1 - pts_I_J_KM1);
if(uSlice==0)
{
col1[0]=1.0;
}
else
{
if(uSlice==1)
{
col2[1]=1.0;
}
else
{
col3[2]=1.0;
}
}
/*
Jacobian is given by
| dx/di, dx/dj, dx/dk |
| dy/di, dy/dj, dy/dk |
| dz/di, dz/dj, dz/dk |
where d == partial derivative
*/
mat3 J = mat3(col1, col2, col3);
return J;
}
void main(void)
{
// determine the structured coordinate for the current location.
vec3 tcoord;
if(uSlice==0)
{
tcoord=vec3(0,gl_TexCoord[0].st);
}
else
{
if(uSlice==1)
{
tcoord=vec3(gl_TexCoord[0].s,0,gl_TexCoord[0].t);
}
else
{
tcoord=vec3(gl_TexCoord[0].st, 0);
}
}
ivec3 ijk = getIJK(tcoord, uDimensions);
// compute partial derivative for X.
mat3 J = jacobian(ijk, uDimensions, texPoints);
// compute inverse of J.
vec3 vector = getVector(ijk, uDimensions, texVectorField);
float detJ=determinant(J);
mat3 invJ = inverse(J,detJ);
gl_FragData[0] = vec4(invJ*vector, 1.0);
//gl_FragData[0] = vec4(vector, 1.0);
// gl_FragData[0] = vec4(detJ);
// gl_FragData[0] = vec4(J[2],1.0);
}
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