GLITCH(1)
General Commands Manual
GLITCH(1)
glitch |
[-cfimprxy] [-a
filters] [-d
filters] [-o
file] [file ...] |
glitch misinterprets PNG files according
to the options given to create natural glitch effects.
The arguments are as follows:
-a
filters- Apply a pattern of comma-separated filters. Filters are
none, sub,
up, average,
paeth.
-c- Write to standard output.
-d
filters- Declare a pattern of comma-separated filters. See
-a for list of filters.
-f- Apply filtering in place of reconstruction.
-i- Invert image data after filtering.
-m- Mirror scanlines after filtering.
-o
file- Write to file.
-p- Use a broken Paeth predictor function.
-r- Apply reconstruction in place of filtering.
-x- Zero first pixel of each scanline after filtering.
-y- Zero first scanline after filtering.
glitch.c in git
/* Copyright (C) 2018, 2021 June McEnroe <june@causal.agency>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <err.h>
#include <inttypes.h>
#include <limits.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <zlib.h>
#define ARRAY_LEN(a) (sizeof(a) / sizeof(a[0]))
static const char *path;
static FILE *file;
static uint32_t crc;
static void pngRead(void *ptr, size_t len, const char *desc) {
size_t n = fread(ptr, len, 1, file);
if (!n && ferror(file)) err(1, "%s", path);
if (!n) errx(1, "%s: missing %s", path, desc);
crc = crc32(crc, ptr, len);
}
static void pngWrite(const void *ptr, size_t len) {
size_t n = fwrite(ptr, len, 1, file);
if (!n) err(1, "%s", path);
crc = crc32(crc, ptr, len);
}
static const uint8_t Sig[8] = "\x89PNG\r\n\x1A\n";
static void sigRead(void) {
uint8_t sig[sizeof(Sig)];
pngRead(sig, sizeof(sig), "signature");
if (memcmp(sig, Sig, sizeof(sig))) {
errx(1, "%s: invalid signature", path);
}
}
static void sigWrite(void) {
pngWrite(Sig, sizeof(Sig));
}
static uint32_t u32Read(const char *desc) {
uint8_t b[4];
pngRead(b, sizeof(b), desc);
return (uint32_t)b[0] << 24 | (uint32_t)b[1] << 16
| (uint32_t)b[2] << 8 | (uint32_t)b[3];
}
static void u32Write(uint32_t x) {
uint8_t b[4] = { x >> 24 & 0xFF, x >> 16 & 0xFF, x >> 8 & 0xFF, x & 0xFF };
pngWrite(b, sizeof(b));
}
struct Chunk {
uint32_t len;
char type[5];
};
static struct Chunk chunkRead(void) {
struct Chunk chunk;
chunk.len = u32Read("chunk length");
crc = crc32(0, Z_NULL, 0);
pngRead(chunk.type, 4, "chunk type");
chunk.type[4] = 0;
return chunk;
}
static void chunkWrite(struct Chunk chunk) {
u32Write(chunk.len);
crc = crc32(0, Z_NULL, 0);
pngWrite(chunk.type, 4);
}
static void crcRead(void) {
uint32_t expect = crc;
uint32_t actual = u32Read("CRC32");
if (actual == expect) return;
errx(
1, "%s: expected CRC32 %08X, found %08X",
path, expect, actual
);
}
static void crcWrite(void) {
u32Write(crc);
}
static void chunkSkip(struct Chunk chunk) {
if (!(chunk.type[0] & 0x20)) {
errx(1, "%s: unsupported critical chunk %s", path, chunk.type);
}
uint8_t buf[4096];
while (chunk.len > sizeof(buf)) {
pngRead(buf, sizeof(buf), "chunk data");
chunk.len -= sizeof(buf);
}
if (chunk.len) pngRead(buf, chunk.len, "chunk data");
crcRead();
}
enum Color {
Grayscale = 0,
Truecolor = 2,
Indexed = 3,
GrayscaleAlpha = 4,
TruecolorAlpha = 6,
};
enum Compression {
Deflate,
};
enum FilterMethod {
Adaptive,
};
enum Interlace {
Progressive,
Adam7,
};
enum { HeaderLen = 13 };
static struct {
uint32_t width;
uint32_t height;
uint8_t depth;
uint8_t color;
uint8_t compression;
uint8_t filter;
uint8_t interlace;
} header;
static size_t pixelLen;
static size_t lineLen;
static size_t dataLen;
static void recalc(void) {
size_t pixelBits = header.depth;
switch (header.color) {
break; case GrayscaleAlpha: pixelBits *= 2;
break; case Truecolor: pixelBits *= 3;
break; case TruecolorAlpha: pixelBits *= 4;
}
pixelLen = (pixelBits + 7) / 8;
lineLen = (header.width * pixelBits + 7) / 8;
dataLen = (1 + lineLen) * header.height;
}
static void (struct Chunk chunk) {
if (chunk.len != HeaderLen) {
errx(
1, "%s: expected %s length %" PRIu32 ", found %" PRIu32,
path, chunk.type, (uint32_t)HeaderLen, chunk.len
);
}
header.width = u32Read("header width");
header.height = u32Read("header height");
pngRead(&header.depth, 1, "header depth");
pngRead(&header.color, 1, "header color");
pngRead(&header.compression, 1, "header compression");
pngRead(&header.filter, 1, "header filter");
pngRead(&header.interlace, 1, "header interlace");
crcRead();
recalc();
}
static void (void) {
struct Chunk ihdr = { HeaderLen, "IHDR" };
chunkWrite(ihdr);
u32Write(header.width);
u32Write(header.height);
pngWrite(&header.depth, 1);
pngWrite(&header.color, 1);
pngWrite(&header.compression, 1);
pngWrite(&header.filter, 1);
pngWrite(&header.interlace, 1);
crcWrite();
}
static struct {
uint32_t len;
uint8_t rgb[256][3];
} pal;
static struct {
uint32_t len;
uint8_t a[256];
} trans;
static void palClear(void) {
pal.len = 0;
trans.len = 0;
}
static void palRead(struct Chunk chunk) {
if (chunk.len % 3) {
errx(
1, "%s: %s length %" PRIu32 " not divisible by 3",
path, chunk.type, chunk.len
);
}
pal.len = chunk.len / 3;
if (pal.len > 256) {
errx(
1, "%s: %s length %" PRIu32 " > 256",
path, chunk.type, pal.len
);
}
pngRead(pal.rgb, chunk.len, "palette data");
crcRead();
}
static void palWrite(void) {
struct Chunk plte = { 3 * pal.len, "PLTE" };
chunkWrite(plte);
pngWrite(pal.rgb, plte.len);
crcWrite();
}
static void transRead(struct Chunk chunk) {
trans.len = chunk.len;
if (trans.len > 256) {
errx(
1, "%s: %s length %" PRIu32 " > 256",
path, chunk.type, trans.len
);
}
pngRead(trans.a, chunk.len, "transparency data");
crcRead();
}
static void transWrite(void) {
struct Chunk trns = { trans.len, "tRNS" };
chunkWrite(trns);
pngWrite(trans.a, trns.len);
crcWrite();
}
static uint8_t *data;
static void dataAlloc(void) {
data = malloc(dataLen);
if (!data) err(1, "malloc");
}
static void dataRead(struct Chunk chunk) {
z_stream stream = { .next_out = data, .avail_out = dataLen };
int error = inflateInit(&stream);
if (error != Z_OK) errx(1, "inflateInit: %s", stream.msg);
for (;;) {
if (strcmp(chunk.type, "IDAT")) {
errx(1, "%s: missing IDAT chunk", path);
}
uint8_t *idat = malloc(chunk.len);
if (!idat) err(1, "malloc");
pngRead(idat, chunk.len, "image data");
crcRead();
stream.next_in = idat;
stream.avail_in = chunk.len;
error = inflate(&stream, Z_SYNC_FLUSH);
free(idat);
if (error == Z_STREAM_END) break;
if (error != Z_OK) {
errx(1, "%s: inflate: %s", path, stream.msg);
}
chunk = chunkRead();
}
inflateEnd(&stream);
if ((size_t)stream.total_out != dataLen) {
errx(
1, "%s: expected data length %zu, found %zu",
path, dataLen, (size_t)stream.total_out
);
}
}
static void dataWrite(void) {
z_stream stream = {
.next_in = data,
.avail_in = dataLen,
};
int error = deflateInit2(
&stream, Z_BEST_COMPRESSION, Z_DEFLATED, 15, 8, Z_FILTERED
);
if (error != Z_OK) errx(1, "deflateInit2: %s", stream.msg);
uLong bound = deflateBound(&stream, dataLen);
uint8_t *buf = malloc(bound);
if (!buf) err(1, "malloc");
stream.next_out = buf;
stream.avail_out = bound;
deflate(&stream, Z_FINISH);
deflateEnd(&stream);
struct Chunk idat = { stream.total_out, "IDAT" };
chunkWrite(idat);
pngWrite(buf, stream.total_out);
crcWrite();
free(buf);
struct Chunk iend = { 0, "IEND" };
chunkWrite(iend);
crcWrite();
}
enum Filter {
None,
Sub,
Up,
Average,
Paeth,
FilterCap,
};
struct Bytes {
uint8_t x, a, b, c;
};
static bool brokenPaeth;
static uint8_t paethPredictor(struct Bytes f) {
int32_t p = (int32_t)f.a + (int32_t)f.b - (int32_t)f.c;
int32_t pa = labs(p - (int32_t)f.a);
int32_t pb = labs(p - (int32_t)f.b);
int32_t pc = labs(p - (int32_t)f.c);
if (pa <= pb && pa <= pc) return f.a;
if (brokenPaeth) {
if (pb < pc) return f.b;
} else {
if (pb <= pc) return f.b;
}
return f.c;
}
static uint8_t recon(enum Filter type, struct Bytes f) {
switch (type) {
case None: return f.x;
case Sub: return f.x + f.a;
case Up: return f.x + f.b;
case Average: return f.x + ((uint32_t)f.a + (uint32_t)f.b) / 2;
case Paeth: return f.x + paethPredictor(f);
default: abort();
}
}
static uint8_t filt(enum Filter type, struct Bytes f) {
switch (type) {
case None: return f.x;
case Sub: return f.x - f.a;
case Up: return f.x - f.b;
case Average: return f.x - ((uint32_t)f.a + (uint32_t)f.b) / 2;
case Paeth: return f.x - paethPredictor(f);
default: abort();
}
}
static uint8_t *lineType(uint32_t y) {
return &data[y * (1 + lineLen)];
}
static uint8_t *lineData(uint32_t y) {
return 1 + lineType(y);
}
static struct Bytes origBytes(uint32_t y, size_t i) {
bool a = (i >= pixelLen), b = (y > 0), c = (a && b);
return (struct Bytes) {
.x = lineData(y)[i],
.a = (a ? lineData(y)[i-pixelLen] : 0),
.b = (b ? lineData(y-1)[i] : 0),
.c = (c ? lineData(y-1)[i-pixelLen] : 0),
};
}
static bool reconFilter;
static void dataRecon(void) {
for (uint32_t y = 0; y < header.height; ++y) {
for (size_t i = 0; i < lineLen; ++i) {
if (reconFilter) {
lineData(y)[i] = filt(*lineType(y), origBytes(y, i));
} else {
lineData(y)[i] = recon(*lineType(y), origBytes(y, i));
}
}
*lineType(y) = None;
}
}
static bool filterRecon;
static size_t applyFilter;
static enum Filter applyFilters[256];
static size_t declFilter;
static enum Filter declFilters[256];
static void dataFilter(void) {
uint8_t *filter[FilterCap];
for (enum Filter i = None; i < FilterCap; ++i) {
filter[i] = malloc(lineLen);
if (!filter[i]) err(1, "malloc");
}
for (uint32_t y = header.height-1; y < header.height; --y) {
uint32_t heuristic[FilterCap] = {0};
enum Filter minType = None;
for (enum Filter type = None; type < FilterCap; ++type) {
for (size_t i = 0; i < lineLen; ++i) {
if (filterRecon) {
filter[type][i] = recon(type, origBytes(y, i));
} else {
filter[type][i] = filt(type, origBytes(y, i));
}
heuristic[type] += abs((int8_t)filter[type][i]);
}
if (heuristic[type] < heuristic[minType]) minType = type;
}
if (declFilter) {
*lineType(y) = declFilters[y % declFilter];
} else {
*lineType(y) = minType;
}
if (applyFilter) {
memcpy(lineData(y), filter[applyFilters[y % applyFilter]], lineLen);
} else {
memcpy(lineData(y), filter[minType], lineLen);
}
}
for (enum Filter i = None; i < FilterCap; ++i) {
free(filter[i]);
}
}
static bool invertData;
static bool mirrorData;
static bool zeroX;
static bool zeroY;
static void glitch(const char *inPath, const char *outPath) {
if (inPath) {
path = inPath;
file = fopen(path, "r");
if (!file) err(1, "%s", path);
} else {
path = "stdin";
file = stdin;
}
sigRead();
struct Chunk ihdr = chunkRead();
if (strcmp(ihdr.type, "IHDR")) {
errx(1, "%s: expected IHDR, found %s", path, ihdr.type);
}
headerRead(ihdr);
if (header.interlace != Progressive) {
errx(1, "%s: unsupported interlacing", path);
}
palClear();
dataAlloc();
for (;;) {
struct Chunk chunk = chunkRead();
if (!strcmp(chunk.type, "PLTE")) {
palRead(chunk);
} else if (!strcmp(chunk.type, "tRNS")) {
transRead(chunk);
} else if (!strcmp(chunk.type, "IDAT")) {
dataRead(chunk);
} else if (!strcmp(chunk.type, "IEND")) {
break;
} else {
chunkSkip(chunk);
}
}
fclose(file);
dataRecon();
dataFilter();
if (invertData) {
for (uint32_t y = 0; y < header.height; ++y) {
for (size_t i = 0; i < lineLen; ++i) {
lineData(y)[i] ^= 0xFF;
}
}
}
if (mirrorData) {
for (uint32_t y = 0; y < header.height; ++y) {
for (size_t i = 0, j = lineLen-1; i < j; ++i, --j) {
uint8_t x = lineData(y)[i];
lineData(y)[i] = lineData(y)[j];
lineData(y)[j] = x;
}
}
}
if (zeroX) {
for (uint32_t y = 0; y < header.height; ++y) {
memset(lineData(y), 0, pixelLen);
}
}
if (zeroY) {
memset(lineData(0), 0, lineLen);
}
char buf[PATH_MAX];
if (outPath) {
path = outPath;
if (outPath == inPath) {
snprintf(buf, sizeof(buf), "%sg", outPath);
file = fopen(buf, "wx");
if (!file) err(1, "%s", buf);
} else {
file = fopen(path, "w");
if (!file) err(1, "%s", outPath);
}
} else {
path = "stdout";
file = stdout;
}
sigWrite();
headerWrite();
if (header.color == Indexed) {
palWrite();
if (trans.len) transWrite();
}
dataWrite();
free(data);
int error = fclose(file);
if (error) err(1, "%s", path);
if (outPath && outPath == inPath) {
error = rename(buf, outPath);
if (error) err(1, "%s", outPath);
}
}
static enum Filter parseFilter(const char *str) {
switch (str[0]) {
case 'N': case 'n': return None;
case 'S': case 's': return Sub;
case 'U': case 'u': return Up;
case 'A': case 'a': return Average;
case 'P': case 'p': return Paeth;
default: errx(1, "invalid filter type %s", str);
}
}
static size_t parseFilters(enum Filter *filters, char *str) {
size_t len = 0;
while (str) {
char *filt = strsep(&str, ",");
filters[len++] = parseFilter(filt);
}
return len;
}
int main(int argc, char *argv[]) {
bool stdio = false;
char *outPath = NULL;
for (int opt; 0 < (opt = getopt(argc, argv, "a:cd:fimo:prxy"));) {
switch (opt) {
break; case 'a': applyFilter = parseFilters(applyFilters, optarg);
break; case 'c': stdio = true;
break; case 'd': declFilter = parseFilters(declFilters, optarg);
break; case 'f': reconFilter = true;
break; case 'i': invertData = true;
break; case 'm': mirrorData = true;
break; case 'o': outPath = optarg;
break; case 'p': brokenPaeth = true;
break; case 'r': filterRecon = true;
break; case 'x': zeroX = true;
break; case 'y': zeroY = true;
break; default: return 1;
}
}
if (optind < argc) {
for (int i = optind; i < argc; ++i) {
glitch(argv[i], (stdio ? NULL : outPath ? outPath : argv[i]));
}
} else {
glitch(NULL, outPath);
}
}