1 files changed, 247 insertions, 0 deletions
diff --git a/tools/ico2png.c b/tools/ico2png.c
new file mode 100644
index 0000000..71644b6
--- /dev/null
+++ b/tools/ico2png.c
@@ -0,0 +1,247 @@
+/* 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);
+		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);
+
+	// Copy the palette, reserving index 0 for transparency. We assume at most
+	// 255 colors will be used by the icon.
+	SDL_RWseek(ico, bestIcon.offset, RW_SEEK_SET);
+	Uint32 dibHeaderLength = SDL_ReadLE32(ico);
+	Uint32 paletteCount = 1 << bestIcon.bpp;
+	Uint8 *palette = calloc(1 + paletteCount, 3);
+	if (!palette) errx(1, "calloc failed");
+	if (dibHeaderLength == 0x0C) {
+		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);
+		}
+	} else if (dibHeaderLength == 0x28) {
+		SDL_RWseek(ico, 0x1C, RW_SEEK_CUR);
+		paletteCount = SDL_ReadLE32(ico);
+		if (!paletteCount) paletteCount = 1 << bestIcon.bpp;
+		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);
+		}
+	} else {
+		errx(
+			1, "%s: unrecognized DIB header length %u",
+			icoPath, dibHeaderLength
+		);
+	}
+	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);
+}