Function:ns2cisc
From S2PLOT
Revision as of 01:10, 30 October 2007
ns2cisc
Create an isosurface object with a colour function
Prototype
int ns2cis(float ***grid, int adim, int bdim, int cdim, int a1, int a2, int b1, int b2, int c1, int c2,
float *tr, float level, int resolution, char trans, float alpha,
void(*fcol)(float*,float*,float*,float*,float*,float*));
</code>
Description
Draw an isosurface of a data volume, at given level, using a function to calculate the colour over the surface. The data in grid is a three-dimensional volume indexed by:
grid[0..(adim-1)][0..(bdim-1)][0..(cdim-1)].
The slice of data actually plotted is indexed by [a1..a2][b1..b2][c1..c2] (as for s2vect3, for example).
tr is the transformation matrix which maps indices into the grid onto the x, y and z axes of the 3d world space. The standard (non-rotated, non-skewed) transformation would have tr[2], tr[3], tr[5], tr[7], tr[9] and tr[10] all zero.
The transformation matrix is:
- x = tr[0] + tr[1] * ia + tr[2] * ib + tr[3] * ic
- y = tr[4] + tr[5] * ia + tr[6] * ib + tr[7] * ic
- z = tr[8] + tr[9] * ia + tr[10]* ib + tr[11]* ic
Provide tr = NULL to use the default, unit transformation.
level gives the level at which the isosurface should be drawn. Skip every nth cell as given by resolution. If n = 1 then no skipping occurs.
Transparency of the surface is controlled by the alpha-channel parameter, alpha, between 0 and 1, and trans:
- trans = 'o' for opaque;
- trans = 't' for "piling up"; and
- trans = 's' for transparency that can occlude.
The colour of the isosurface is specified by the function:
fcol(float *x, float *y, float *z, float *r, float *g, float *b)
which returns pointers to RGB colour values.
See Also
ns2cis Create an isosurface object ns2dis Draw an isosurface object ns2sisl Change the level of isosurface s2vect3 Draw a vector map of a 3D data array, with blanking. struct_COLOUR Data structure for (r,g,b) colour indices.
Code Example
<code>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "s2plot.h"
#define CELLS 30
void colorfn(float *x, float *y, float *z, float *r, float *g, float *b)
/* Isosurface colouring function */
{
*r = 0.2 + 0.5 * (*x) / (float)(CELLS - 1);
*g = 0.0 + 0.8 * (*y) / (float)(CELLS - 1);
*b = 0.6 + 0.2 * (*z) / (float)(CELLS - 1);
}
int main(int argc, char *argv[])
{
int i, j, k; /* Loop variables */
float x, y, z; /* Dummy variables for grid values */
int nx, ny, nz; /* Number of cells in grid */
float ***grid; /* Grid data */
float tr[12]; /* Transformation matrix */
int resolution; /* Resolution of isosurface */
float level; /* Isosurface level to plot */
float alpha; /* Alpha channel */
char trans; /* Drawing mode for isosurface */
int id1, id2; /* ID for isosurface objects */
nx = CELLS; /* Grid dimensions */
ny = CELLS;
nz = CELLS;
/* Create transpose matrix mapping data indices to world coords */
tr[0] = tr[4] = tr[8] = 0.0; /* Offsets */
tr[1] = tr[6] = tr[11] = 1.0; /* Increments */
tr[2] = tr[3] = tr[5] = tr[7] = tr[9] = tr[10] = 0.; /* Cross terms */
s2opend("/?",argc, argv); /* Open the display */
s2swin(0, nx-1, 0, ny-1, 0, nz-1); /* Set the window coordinates */
s2box("BCDET",0,0,"BCDET",0,0,"BCDET",0,0); /* Draw coordinate box */
/* allocate and generate the data grid */
grid = (float ***)malloc(nx * sizeof(float **));
for (i = 0; i < nx; i++) {
grid[i] = (float **)malloc(ny * sizeof(float *));
x = (float)(i) / (float)(nx - 1);
for (j = 0; j < ny; j++) {
grid[i][j] = (float *)malloc(nz * sizeof(float));
y = (float)(j) / (float)(ny - 1);
for (k = 0; k < nz; k++) {
z = (float)(k) / (float)(nz - 1);
grid[i][j][k] = x*x*x + y*y - z*z*z*z;
}
}
}
level = 0.2; /* Set the isosurface level */
resolution = 1; /* Set the isosurface resolution */
alpha = 0.9; /* Set the alpha channel */
trans = 'o'; /* Opaque isosurface */
/* Create the isosurface object */
id1 = ns2cis(grid, nx, ny, nz, 0, nx-1, 0, ny-1, 0, nz-1,
tr, level, resolution, trans, alpha, 1., 1., 0.);
ns2dis(id1, 0); /* Draw it */
level = 0.7; /* Set the isosurface level */
resolution = 6; /* Set the isosurface resolution */
alpha = 0.5; /* Set the alpha channel */
trans = 's'; /* Opaque isosurface */
/* Create the isosurface object */
id2 = ns2cisc(grid, nx, ny, nz, 0, nx-1, 0, ny-1, 0, nz-1,
tr, level, resolution, trans, alpha, colorfn);
ns2dis(id2, 0); /* Draw it */
s2show(1); /* Open the s2plot window */
return 1;
}
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