void DisplaceOperation::pixelTransform(const float xy[2], float r_uv[2], float r_deriv[2][2])
{
float col[4];
float uv[2]; /* temporary variables for derivative estimation */
int num;
m_inputScaleXProgram->readSampled(col, xy[0], xy[1], COM_PS_NEAREST);
float xs = col[0];
m_inputScaleYProgram->readSampled(col, xy[0], xy[1], COM_PS_NEAREST);
float ys = col[0];
/* clamp x and y displacement to triple image resolution -
* to prevent hangs from huge values mistakenly plugged in eg. z buffers */
CLAMP(xs, -m_width_x4, m_width_x4);
CLAMP(ys, -m_height_x4, m_height_x4);
/* displaced pixel in uv coords, for image sampling */
read_displacement(xy[0], xy[1], xs, ys, xy, r_uv[0], r_uv[1]);
/* Estimate partial derivatives using 1-pixel offsets */
const float epsilon[2] = { 1.0f, 1.0f };
zero_v2(r_deriv[0]);
zero_v2(r_deriv[1]);
num = 0;
if (read_displacement(xy[0] + epsilon[0], xy[1], xs, ys, xy, uv[0], uv[1])) {
r_deriv[0][0] += uv[0] - r_uv[0];
r_deriv[1][0] += uv[1] - r_uv[1];
++num;
}
if (read_displacement(xy[0] - epsilon[0], xy[1], xs, ys, xy, uv[0], uv[1])) {
r_deriv[0][0] += r_uv[0] - uv[0];
r_deriv[1][0] += r_uv[1] - uv[1];
++num;
}
if (num > 0) {
float numinv = 1.0f / (float)num;
r_deriv[0][0] *= numinv;
r_deriv[1][0] *= numinv;
}
num = 0;
if (read_displacement(xy[0], xy[1] + epsilon[1], xs, ys, xy, uv[0], uv[1])) {
r_deriv[0][1] += uv[0] - r_uv[0];
r_deriv[1][1] += uv[1] - r_uv[1];
++num;
}
if (read_displacement(xy[0], xy[1] - epsilon[1], xs, ys, xy, uv[0], uv[1])) {
r_deriv[0][1] += r_uv[0] - uv[0];
r_deriv[1][1] += r_uv[1] - uv[1];
++num;
}
if (num > 0) {
float numinv = 1.0f / (float)num;
r_deriv[0][1] *= numinv;
r_deriv[1][1] *= numinv;
}
}
int main(int argc, char **argv)
{
/* Read command line arguments */
read_command_line(argc,argv);
/* Read Parameters from parameter file */
read_parameters();
/* read box from file header */
if (box_from_header) read_box(infilename);
/* Initialize cell data structures */
init_cells();
/* Read coordinates and displacement */
read_displacement(infilename);
/* Calculate strain tensor */
calc_strain();
/* Output strain tensor */
write_data();
return 0;
}
