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/*
* Copyright (C) 2011-2013 Karlsruhe Institute of Technology
*
* This file is part of Ufo.
*
* This library is free software: you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation, either
* version 3 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library. If not, see <http://www.gnu.org/licenses/>.
*/
constant sampler_t sampler = CLK_NORMALIZED_COORDS_FALSE |
CLK_ADDRESS_CLAMP |
CLK_FILTER_NEAREST;
kernel void
forwardproject(read_only image2d_t slice,
global float *sinogram,
float axis_pos,
float angle_step)
{
const int idx = get_global_id(0);
const int idy = get_global_id(1);
const int slice_width = get_global_size(0);
const float angle = idy * angle_step;
/* radius of object circle */
const float r = fmin (axis_pos, slice_width - axis_pos);
/* positive/negative distance from detector center */
const float d = idx - axis_pos + 0.5f;
/* length of the cut through the circle */
const float l = sqrt(8.0f*r*r - 4.0f*d*d);
/* vector in detector direction */
float2 D = (float2) (cos(angle), -sin(angle));
D = normalize(D);
/* vector perpendicular to the detector */
const float2 N = (float2) (D.y, -D.x);
/* sample point in the circle traveling along N */
float2 sample = d * D - l/2.0f * N + ((float2) (axis_pos, axis_pos));
float sum = 0.0f;
for (int i = 0; i < l; i++) {
sum += read_imagef(slice, sampler, sample).x;
sample += N;
}
sinogram[idy * slice_width + idx] = sum;
}
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