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/* Copyright (C) 2022 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 <SDL_rwops.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
static void errx(int eval, const char *fmt, ...) {
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
va_end(ap);
putc('\n', stderr);
exit(eval);
}
static void err(int eval, const char *fmt, ...) {
va_list ap;
va_start(ap, fmt);
vfprintf(stderr, fmt, ap);
va_end(ap);
fprintf(stderr, ": %s\n", SDL_GetError());
exit(eval);
}
static Uint32 crcTable(Uint8 n) {
static Uint32 table[256];
if (table[1]) return table[n];
for (int i = 0; i < 256; ++i) {
table[i] = i;
for (int j = 0; j < 8; ++j) {
table[i] = (table[i] >> 1) ^ (table[i] & 1 ? 0xEDB88320 : 0);
}
}
return table[n];
}
static Uint32 pngCRC;
static void pngWrite(SDL_RWops *rw, const Uint8 *ptr, Uint32 len) {
if (!SDL_RWwrite(rw, ptr, len, 1)) err(1, "pngWrite");
for (Uint32 i = 0; i < len; ++i) {
pngCRC = crcTable(pngCRC ^ ptr[i]) ^ (pngCRC >> 8);
}
}
static void pngUint32(SDL_RWops *rw, Uint32 n) {
Uint8 bytes[4] = { n >> 24, n >> 16, n >> 8, n };
pngWrite(rw, bytes, sizeof(bytes));
}
static void pngChunk(SDL_RWops *rw, const char *type, Uint32 len) {
pngUint32(rw, len);
pngCRC = ~0;
pngWrite(rw, (const Uint8 *)type, 4);
}
// Write out image data as DEFLATE literal blocks
static void pngData(SDL_RWops *rw, const Uint8 *data, Uint32 len) {
Uint32 adler1 = 1, adler2 = 0;
for (Uint32 i = 0; i < len; ++i) {
adler1 = (adler1 + data[i]) % 65521;
adler2 = (adler1 + adler2) % 65521;
}
Uint32 zlen = 2 + 5 * ((len + 0xFFFE) / 0xFFFF) + len + 4;
pngChunk(rw, "IDAT", zlen);
Uint8 zlib[2] = { 0x08, 0x1D };
pngWrite(rw, zlib, sizeof(zlib));
for (; len > 0xFFFF; data += 0xFFFF, len -= 0xFFFF) {
Uint8 block[5] = { 0x00, 0xFF, 0xFF, 0x00, 0x00 };
pngWrite(rw, block, sizeof(block));
pngWrite(rw, data, 0xFFFF);
}
Uint8 block[5] = { 0x01, len, len >> 8, ~len, ~len >> 8 };
pngWrite(rw, block, sizeof(block));
pngWrite(rw, data, len);
pngUint32(rw, adler2 << 16 | adler1);
pngUint32(rw, ~pngCRC);
}
int main(int argc, char *argv[]) {
if (argc < 2) return 1;
const char *icoPath = argv[1];
const char *name = strrchr(icoPath, '/');
name = (name ? &name[1] : icoPath);
char pngPath[256];
snprintf(
pngPath, sizeof(pngPath), "%.*s.PNG", (int)strcspn(name, "."), name
);
SDL_RWops *ico = SDL_RWFromFile(icoPath, "rb");
if (!ico) err(1, "%s", icoPath);
// Read the ICONHEADER
// https://devblogs.microsoft.com/oldnewthing/20101018-00/?p=12513
SDL_ReadLE16(ico); // reserved
if (SDL_ReadLE16(ico) != 0x0001) {
errx(1, "%s: not an ICO", icoPath);
}
Uint16 count = SDL_ReadLE16(ico);
// Find the best icon
Uint32 bestScore = 0;
struct Icon {
Uint8 width;
Uint8 height;
Uint8 colors;
Uint16 planes;
Uint16 bpp;
Uint32 length;
Uint32 offset;
} bestIcon = {0};
for (Uint16 i = 0; i < count; ++i) {
struct Icon icon = {0};
icon.width = SDL_ReadU8(ico);
icon.height = SDL_ReadU8(ico);
icon.colors = SDL_ReadU8(ico);
SDL_ReadU8(ico); // reserved
icon.planes = SDL_ReadLE16(ico);
icon.bpp = SDL_ReadLE16(ico); // some ICOs lie about this...
icon.length = SDL_ReadLE32(ico);
icon.offset = SDL_ReadLE32(ico);
Uint32 score = icon.width * icon.height * icon.colors;
if (score > bestScore) {
bestScore = score;
bestIcon = icon;
}
}
if (!bestScore) errx(1, "%s: no icons found", icoPath);
if (bestIcon.planes != 1) {
errx(1, "%s: non-indexed bitmap not implemented", icoPath);
}
SDL_RWops *png = SDL_RWFromFile(pngPath, "wb");
if (!png) err(1, "%s", pngPath);
// Write the PNG header
SDL_RWwrite(png, "\x89PNG\r\n\x1A\n", 8, 1);
pngChunk(png, "IHDR", 13);
pngUint32(png, bestIcon.width);
pngUint32(png, bestIcon.height);
Uint8 depth = 8;
Uint8 color = 3; // indexed
Uint8 zero[3] = {0};
pngWrite(png, &depth, 1);
pngWrite(png, &color, 1);
pngWrite(png, zero, 3);
pngUint32(png, ~pngCRC);
// Read the real bpp and palette count from the DIB header
SDL_RWseek(ico, bestIcon.offset, RW_SEEK_SET);
Uint32 dibHeaderLength = SDL_ReadLE32(ico);
if (dibHeaderLength != 0x28) {
errx(
1, "%s: unrecognized DIB header length %u",
icoPath, dibHeaderLength
);
}
SDL_RWseek(ico, 0x0A, RW_SEEK_CUR);
bestIcon.bpp = SDL_ReadLE16(ico); // the truth
SDL_RWseek(ico, 0x10, RW_SEEK_CUR);
Uint32 paletteCount = SDL_ReadLE32(ico);
if (!paletteCount) paletteCount = 1 << bestIcon.bpp;
// Copy the palette, reserving index 0 for transparency. We assume at most
// 255 colors will be used by the icon.
Uint8 *palette = calloc(1 + paletteCount, 3);
if (!palette) errx(1, "calloc failed");
SDL_RWseek(ico, bestIcon.offset + dibHeaderLength, RW_SEEK_SET);
for (Uint32 i = 0; i < paletteCount; ++i) {
palette[3 * (i + 1) + 2] = SDL_ReadU8(ico);
palette[3 * (i + 1) + 1] = SDL_ReadU8(ico);
palette[3 * (i + 1) + 0] = SDL_ReadU8(ico);
SDL_ReadU8(ico);
}
pngChunk(png, "PLTE", 3 * (1 + paletteCount));
pngWrite(png, palette, 3 * (1 + paletteCount));
pngUint32(png, ~pngCRC);
pngChunk(png, "tRNS", 1);
pngWrite(png, zero, 1);
pngUint32(png, ~pngCRC);
free(palette);
Uint32 pngStride = 1 + bestIcon.width;
Uint8 *lines = calloc(bestIcon.height, pngStride);
if (!lines) errx(1, "calloc failed");
// Copy and expand the icon pixels to 8 bpp, adding 1 for the transparency
// index.
Uint32 icoPPByte = 8 / bestIcon.bpp;
Uint32 icoStride = bestIcon.width / icoPPByte;
icoStride += -icoStride & 0x03;
for (Uint32 y = bestIcon.height - 1; y < bestIcon.height; --y) {
Uint8 *ptr = &lines[y * pngStride + 1];
Uint8 *end = &lines[(y + 1) * pngStride];
for (Uint32 x = 0; x < icoStride; ++x) {
Uint8 byte = SDL_ReadU8(ico);
for (Uint8 i = icoPPByte - 1; i < icoPPByte; --i) {
if (ptr == end) break;
*ptr = (byte >> (i * bestIcon.bpp)) & ((1 << bestIcon.bpp) - 1);
*ptr++ += 1;
}
}
}
// Read the 1 bpp transparency mask, setting PNG pixels to index 0.
// https://devblogs.microsoft.com/oldnewthing/20101019-00/?p=12503
icoPPByte = 8;
icoStride = bestIcon.width / icoPPByte;
icoStride += -icoStride & 0x03;
for (Uint32 y = bestIcon.height - 1; y < bestIcon.height; --y) {
Uint8 *ptr = &lines[y * pngStride + 1];
Uint8 *end = &lines[(y + 1) * pngStride];
for (Uint32 x = 0; x < icoStride; ++x) {
Uint8 byte = SDL_ReadU8(ico);
for (Uint8 i = icoPPByte - 1; i < icoPPByte; --i) {
if (ptr == end) break;
if ((byte >> i) & 1) *ptr = 0;
ptr++;
}
}
}
pngData(png, lines, bestIcon.height * pngStride);
pngChunk(png, "IEND", 0);
pngUint32(png, ~pngCRC);
free(lines);
SDL_RWclose(png);
SDL_RWclose(ico);
}
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