mpv/video/out/gpu/error_diffusion.c

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/*
* This file is part of mpv.
*
* mpv 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 2.1 of the License, or (at your option) any later version.
*
* mpv 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 mpv. If not, see <http://www.gnu.org/licenses/>.
*/
#include <stdlib.h>
#include "error_diffusion.h"
#include "common/common.h"
#define GLSL(...) gl_sc_addf(sc, __VA_ARGS__)
#define GLSLH(...) gl_sc_haddf(sc, __VA_ARGS__)
// After a (y, x) -> (y, x + y * shift) mapping, find the right most column that
// will be affected by the current column.
static int compute_rightmost_shifted_column(const struct error_diffusion_kernel *k)
{
int ret = 0;
for (int y = 0; y <= EF_MAX_DELTA_Y; y++) {
for (int x = EF_MIN_DELTA_X; x <= EF_MAX_DELTA_X; x++) {
if (k->pattern[y][x - EF_MIN_DELTA_X] != 0) {
int shifted_x = x + y * k->shift;
// The shift mapping guarantees current column (or left of it)
// won't be affected by error diffusion.
assert(shifted_x > 0);
ret = MPMAX(ret, shifted_x);
}
}
}
return ret;
}
const struct error_diffusion_kernel *mp_find_error_diffusion_kernel(const char *name)
{
if (!name)
return NULL;
for (const struct error_diffusion_kernel *k = mp_error_diffusion_kernels;
k->name;
k++) {
if (strcmp(k->name, name) == 0)
return k;
}
return NULL;
}
int mp_ef_compute_shared_memory_size(const struct error_diffusion_kernel *k,
int height)
{
// We add EF_MAX_DELTA_Y empty lines on the bottom to handle errors
// propagated out from bottom side.
int rows = height + EF_MAX_DELTA_Y;
int shifted_columns = compute_rightmost_shifted_column(k) + 1;
// The shared memory is an array of size rows*shifted_columns. Each element
// is a single uint for three RGB component.
return rows * shifted_columns * 4;
}
void pass_error_diffusion(struct gl_shader_cache *sc,
const struct error_diffusion_kernel *k,
int tex, int width, int height, int depth, int block_size)
{
assert(block_size <= height);
// The parallel error diffusion works by applying the shift mapping first.
// Taking the Floyd and Steinberg algorithm for example. After applying
// the (y, x) -> (y, x + y * shift) mapping (with shift=2), all errors are
// propagated into the next few columns, which makes parallel processing on
// the same column possible.
//
// X 7/16 X 7/16
// 3/16 5/16 1/16 ==> 0 0 3/16 5/16 1/16
// Figuring out the size of rectangle containing all shifted pixels.
// The rectangle height is not changed.
int shifted_width = width + (height - 1) * k->shift;
// We process all pixels from the shifted rectangles column by column, with
// a single global work group of size |block_size|.
// Figuring out how many block are required to process all pixels. We need
// this explicitly to make the number of barrier() calls match.
int blocks = (height * shifted_width + block_size - 1) / block_size;
// If we figure out how many of the next columns will be affected while the
// current columns is being processed. We can store errors of only a few
// columns in the shared memory. Using a ring buffer will further save the
// cost while iterating to next column.
int ring_buffer_rows = height + EF_MAX_DELTA_Y;
int ring_buffer_columns = compute_rightmost_shifted_column(k) + 1;
int ring_buffer_size = ring_buffer_rows * ring_buffer_columns;
// Defines the ring buffer in shared memory.
GLSLH("shared uint err_rgb8[%d];\n", ring_buffer_size);
// Initialize the ring buffer.
GLSL("for (int i = int(gl_LocalInvocationIndex); i < %d; i += %d) ",
ring_buffer_size, block_size);
GLSL("err_rgb8[i] = 0u;\n");
GLSL("for (int block_id = 0; block_id < %d; ++block_id) {\n", blocks);
// Add barrier here to have previous block all processed before starting
// the processing of the next.
GLSL("groupMemoryBarrier();\n");
GLSL("barrier();\n");
// Compute the coordinate of the pixel we are currently processing, both
// before and after the shift mapping.
GLSL("int id = int(gl_LocalInvocationIndex) + block_id * %d;\n", block_size);
GLSL("int y = id %% %d, x_shifted = id / %d;\n", height, height);
GLSL("int x = x_shifted - y * %d;\n", k->shift);
// Proceed only if we are processing a valid pixel.
GLSL("if (0 <= x && x < %d) {\n", width);
// The index that the current pixel have on the ring buffer.
GLSL("int idx = (x_shifted * %d + y) %% %d;\n", ring_buffer_rows, ring_buffer_size);
// Fetch the current pixel.
GLSL("vec3 pix = texelFetch(texture%d, ivec2(x, y), 0).rgb;\n", tex);
// The dithering will quantize pixel value into multiples of 1/dither_quant.
int dither_quant = (1 << depth) - 1;
// We encode errors in RGB components into a single 32-bit unsigned integer.
// The error we propagate from the current pixel is in range of
// [-0.5 / dither_quant, 0.5 / dither_quant]. While not quite obvious, the
// sum of all errors been propagated into a pixel is also in the same range.
// It's possible to map errors in this range into [-127, 127], and use an
// unsigned 8-bit integer to store it (using standard two's complement).
// The three 8-bit unsigned integers can then be encoded into a single
// 32-bit unsigned integer, with two 4-bit padding to prevent addition
// operation overflows affecting other component. There are at most 12
// addition operations on each pixel, so 4-bit padding should be enough.
// The overflow from R component will be discarded.
//
// The following figure is how the encoding looks like.
//
// +------------------------------------+
// |RRRRRRRR|0000|GGGGGGGG|0000|BBBBBBBB|
// +------------------------------------+
//
// The bitshift position for R and G component.
int bitshift_r = 24, bitshift_g = 12;
// The multiplier we use to map [-0.5, 0.5] to [-127, 127].
int uint8_mul = 127 * 2;
// Adding the error previously propagated into current pixel, and clear it
// in the buffer.
GLSL("uint err_u32 = err_rgb8[idx] + %uu;\n",
(128u << bitshift_r) | (128u << bitshift_g) | 128u);
GLSL("pix = pix * %d.0 + vec3("
"int((err_u32 >> %d) & 255u) - 128,"
"int((err_u32 >> %d) & 255u) - 128,"
"int( err_u32 & 255u) - 128"
") / %d.0;\n", dither_quant, bitshift_r, bitshift_g, uint8_mul);
GLSL("err_rgb8[idx] = 0u;\n");
// Write the dithered pixel.
GLSL("vec3 dithered = round(pix);\n");
GLSL("imageStore(out_image, ivec2(x, y), vec4(dithered / %d.0, 0.0));\n",
dither_quant);
GLSL("vec3 err_divided = (pix - dithered) * %d.0 / %d.0;\n",
uint8_mul, k->divisor);
GLSL("ivec3 tmp;\n");
// Group error propagation with same weight factor together, in order to
// reduce the number of annoying error encoding.
for (int dividend = 1; dividend <= k->divisor; dividend++) {
bool err_assigned = false;
for (int y = 0; y <= EF_MAX_DELTA_Y; y++) {
for (int x = EF_MIN_DELTA_X; x <= EF_MAX_DELTA_X; x++) {
if (k->pattern[y][x - EF_MIN_DELTA_X] != dividend)
continue;
if (!err_assigned) {
err_assigned = true;
GLSL("tmp = ivec3(round(err_divided * %d.0));\n", dividend);
GLSL("err_u32 = "
"(uint(tmp.r & 255) << %d)|"
"(uint(tmp.g & 255) << %d)|"
" uint(tmp.b & 255);\n",
bitshift_r, bitshift_g);
}
int shifted_x = x + y * k->shift;
// Unlike the right border, errors propagated out from left
// border will remain in the ring buffer. This will produce
// visible artifacts near the left border, especially for
// shift=3 kernels.
if (x < 0)
GLSL("if (x >= %d) ", -x);
// Calculate the new position in the ring buffer to propagate
// the error into.
int ring_buffer_delta = shifted_x * ring_buffer_rows + y;
GLSL("atomicAdd(err_rgb8[(idx + %d) %% %d], err_u32);\n",
ring_buffer_delta, ring_buffer_size);
}
}
}
GLSL("}\n"); // if (0 <= x && x < width)
GLSL("}\n"); // block_id
}
// Different kernels for error diffusion.
// Patterns are from http://www.efg2.com/Lab/Library/ImageProcessing/DHALF.TXT
const struct error_diffusion_kernel mp_error_diffusion_kernels[] = {
{
.name = "simple",
.shift = 1,
.pattern = {{0, 0, 0, 1, 0},
{0, 0, 1, 0, 0},
{0, 0, 0, 0, 0}},
.divisor = 2
},
{
// The "false" Floyd-Steinberg kernel
.name = "false-fs",
.shift = 1,
.pattern = {{0, 0, 0, 3, 0},
{0, 0, 3, 2, 0},
{0, 0, 0, 0, 0}},
.divisor = 8
},
{
.name = "sierra-lite",
.shift = 2,
.pattern = {{0, 0, 0, 2, 0},
{0, 1, 1, 0, 0},
{0, 0, 0, 0, 0}},
.divisor = 4
},
{
.name = "floyd-steinberg",
.shift = 2,
.pattern = {{0, 0, 0, 7, 0},
{0, 3, 5, 1, 0},
{0, 0, 0, 0, 0}},
.divisor = 16
},
{
.name = "atkinson",
.shift = 2,
.pattern = {{0, 0, 0, 1, 1},
{0, 1, 1, 1, 0},
{0, 0, 1, 0, 0}},
.divisor = 8
},
// All kernels below have shift value of 3, and probably are too heavy for
// low end GPU.
{
.name = "jarvis-judice-ninke",
.shift = 3,
.pattern = {{0, 0, 0, 7, 5},
{3, 5, 7, 5, 3},
{1, 3, 5, 3, 1}},
.divisor = 48
},
{
.name = "stucki",
.shift = 3,
.pattern = {{0, 0, 0, 8, 4},
{2, 4, 8, 4, 2},
{1, 2, 4, 2, 1}},
.divisor = 42
},
{
.name = "burkes",
.shift = 3,
.pattern = {{0, 0, 0, 8, 4},
{2, 4, 8, 4, 2},
{0, 0, 0, 0, 0}},
.divisor = 32
},
{
.name = "sierra-3",
.shift = 3,
.pattern = {{0, 0, 0, 5, 3},
{2, 4, 5, 4, 2},
{0, 2, 3, 2, 0}},
.divisor = 32
},
{
.name = "sierra-2",
.shift = 3,
.pattern = {{0, 0, 0, 4, 3},
{1, 2, 3, 2, 1},
{0, 0, 0, 0, 0}},
.divisor = 16
},
{0}
};