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/*
* Copyright (c) 2016-2018 Arm Limited.
*
* SPDX-License-Identifier: MIT
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
#include "helpers.h"
#include "types.h"
/* The map table to retrieve the 16 texels in the Bresenham circle of radius 3 with center in P.
*
* . . F 0 1 . . .
* . E . . . 2 . .
* D . . . . . 3 .
* C . . P . . 4 .
* B . . . . . 5 .
* . A . . . 6 . .
* . . 9 8 7 . . .
*/
constant int offsets_s[16][2] =
{
{ 0, -3 }, // 0
{ 1, -3 }, // 1
{ 2, -2 }, // 2
{ 3, -1 }, // 3
{ 3, 0 }, // 4
{ 3, 1 }, // 5
{ 2, 2 }, // 6
{ 1, 3 }, // 7
{ 0, 3 }, // 8
{ -1, 3 }, // 9
{ -2, 2 }, // A
{ -3, 1 }, // B
{ -3, 0 }, // C
{ -3, -1 }, // D
{ -2, -2 }, // E
{ -1, -3 }, // F
};
/** Load a pixel and set the mask values.
*
* @param[in] ptr The pointer to the starting address of source image
* @param[in] a Index to indicate the position in the Bresenham circle
* @param[in] stride Stride of source image in x dimension
* @param[in] dark The left end of the threshold range
* @param[in] bright The right end of the threshold range
* @param[out] dark_mask The bit-set mask records dark pixels. Its bit is set as 1 if the corresponding pixel is dark
* @param[out] bright_mask The bit-set mask records bright pixels. Its bit is set as 1 if the corresponding pixel is bright
*
*/
#define LOAD_AND_SET_MASK(ptr, a, stride, dark, bright, dark_mask, bright_mask) \
{ \
unsigned char pixel; \
pixel = *(ptr + (int)stride * offsets_s[a][1] + offsets_s[a][0]); \
dark_mask |= (pixel < dark) << a; \
bright_mask |= (pixel > bright) << a; \
}
/** Checks if a pixel is a corner. Pixel is considerred as a corner if the 9 continuous pixels in the Bresenham circle are bright or dark.
*
* @param[in] bright_mask The mask recording postions of bright pixels
* @param[in] dark_mask The mask recording postions of dark pixels
* @param[out] isCorner Indicate whether candidate pixel is corner
*/
#define CHECK_CORNER(bright_mask, dark_mask, isCorner) \
{ \
for(int i = 0; i < 16; i++) \
{ \
isCorner |= ((bright_mask & 0x1FF) == 0x1FF); \
isCorner |= ((dark_mask & 0x1FF) == 0x1FF); \
if(isCorner) \
{ \
break; \
} \
bright_mask >>= 1; \
dark_mask >>= 1; \
} \
}
/* Calculate pixel's strength */
uchar compute_strength(uchar candidate_pixel, __global unsigned char *ptr, unsigned int stride, unsigned char threshold)
{
short a = threshold;
short b = 255;
while(b - a > 1)
{
uchar c = convert_uchar_sat((a + b) / 2);
unsigned int bright_mask = 0;
unsigned int dark_mask = 0;
unsigned char p_bright = add_sat(candidate_pixel, c);
unsigned char p_dark = sub_sat(candidate_pixel, c);
bool isCorner = 0;
for(uint i = 0; i < 16; i++)
{
LOAD_AND_SET_MASK(ptr, i, stride, p_dark, p_bright, dark_mask, bright_mask)
}
bright_mask |= (bright_mask << 16);
dark_mask |= (dark_mask << 16);
CHECK_CORNER(bright_mask, dark_mask, isCorner);
if(isCorner)
{
a = convert_short(c);
}
else
{
b = convert_short(c);
}
}
return a;
}
/** Fast corners implementation. Calculates and returns the strength of each pixel.
*
* The algorithm loops through the 16 pixels in the Bresenham circle and set low 16 bit of masks if corresponding pixel is bright
* or dark. It then copy the low 16 bit to the high 16 bit of the masks. Right shift the bit to check whether the 9 continuous bits
* from the LSB are set.
*
* @param[in] input_ptr Pointer to the first source image. Supported data types: U8
* @param[in] input_stride_x Stride of the first source image in X dimension (in bytes)
* @param[in] input_step_x input_stride_x * number of elements along X processed per workitem(in bytes)
* @param[in] input_stride_y Stride of the first source image in Y dimension (in bytes)
* @param[in] input_step_y input_stride_y * number of elements along Y processed per workitem(in bytes)
* @param[in] input_offset_first_element_in_bytes The offset of the first element in the first source image
* @param[out] output_ptr Pointer to the first source image. Supported data types: U8
* @param[in] output_stride_x Stride of the first source image in X dimension (in bytes)
* @param[in] output_step_x output_stride_x * number of elements along X processed per workitem(in bytes)
* @param[in] output_stride_y Stride of the first source image in Y dimension (in bytes)
* @param[in] output_step_y output_stride_y * number of elements along Y processed per workitem(in bytes)
* @param[in] output_offset_first_element_in_bytes The offset of the first element in the first source image
* @param[in] threshold_value Threshold value.
*
*/
__kernel void fast_corners(
IMAGE_DECLARATION(input),
IMAGE_DECLARATION(output),
float threshold_value)
{
Image in = CONVERT_TO_IMAGE_STRUCT(input);
Image out = CONVERT_TO_IMAGE_STRUCT(output);
const unsigned char threshold = (uchar)threshold_value;
unsigned int bright_mask = 0;
unsigned int dark_mask = 0;
unsigned char isCorner = 0;
unsigned char p = *in.ptr;
unsigned char p_bright = add_sat(p, threshold);
unsigned char p_dark = sub_sat(p, threshold);
LOAD_AND_SET_MASK(in.ptr, 0, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 4, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 8, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 12, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
if(((bright_mask | dark_mask) & 0x1111) == 0)
{
*out.ptr = 0;
return;
}
LOAD_AND_SET_MASK(in.ptr, 1, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 2, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 3, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 5, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 6, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 7, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 9, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 10, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 11, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 13, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 14, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
LOAD_AND_SET_MASK(in.ptr, 15, input_stride_y, p_dark, p_bright, dark_mask, bright_mask)
bright_mask |= (bright_mask << 16);
dark_mask |= (dark_mask << 16);
CHECK_CORNER(bright_mask, dark_mask, isCorner)
if(!isCorner)
{
*out.ptr = 0;
return;
}
#ifdef USE_MAXSUPPRESSION
*out.ptr = compute_strength(p, in.ptr, input_stride_y, threshold);
#else /* USE_MAXSUPPRESSION */
*out.ptr = 1;
#endif /* USE_MAXSUPPRESSION */
}
/** Copy result to Keypoint buffer and count number of corners
*
* @param[in] input_ptr Pointer to the image with calculated strenghs. Supported data types: U8
* @param[in] input_stride_x Stride of the first source image in X dimension (in bytes)
* @param[in] input_step_x input_stride_x * number of elements along X processed per workitem(in bytes)
* @param[in] input_stride_y Stride of the first source image in Y dimension (in bytes)
* @param[in] input_step_y input_stride_y * number of elements along Y processed per workitem(in bytes)
* @param[in] input_offset_first_element_in_bytes The offset of the first element in the first source image
* @param[in] max_num_points The maximum number of keypoints the array can hold
* @param[out] offset The number of skipped pixels in x dimension
* @param[out] num_of_points Number of points found
* @param[out] out The keypoints found
*
*/
__kernel void copy_to_keypoint(
IMAGE_DECLARATION(input),
uint max_num_points,
uint offset,
__global uint *num_of_points,
__global Keypoint *out)
{
#ifndef UPDATE_NUMBER
if(*num_of_points >= max_num_points)
{
return;
}
#endif /* UPDATE_NUMBER */
Image in = CONVERT_TO_IMAGE_STRUCT(input);
uchar value = *in.ptr;
if(value > 0)
{
int id = atomic_inc(num_of_points);
if(id < max_num_points)
{
out[id].strength = value;
out[id].x = get_global_id(0) + offset;
out[id].y = get_global_id(1) + offset;
out[id].tracking_status = 1;
out[id].scale = 0.f;
out[id].orientation = 0.f;
out[id].error = 0.f;
}
}
}
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