1 files changed, 108 insertions, 0 deletions
diff --git a/png.h b/png.h
new file mode 100644
index 0000000..0df4699
--- /dev/null
+++ b/png.h
@@ -0,0 +1,108 @@
+/* Copyright (C) 2018  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 <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sysexits.h>
+
+static inline uint32_t pngCRCTable(uint8_t n) {
+	static uint32_t 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_t pngCRC;
+
+static inline void pngWrite(FILE *file, const uint8_t *ptr, uint32_t len) {
+	if (!fwrite(ptr, len, 1, file)) err(EX_IOERR, "pngWrite");
+	for (uint32_t i = 0; i < len; ++i) {
+		pngCRC = pngCRCTable(pngCRC ^ ptr[i]) ^ (pngCRC >> 8);
+	}
+}
+static inline void pngInt32(FILE *file, uint32_t n) {
+	pngWrite(file, (uint8_t []) { n >> 24, n >> 16, n >> 8, n }, 4);
+}
+static inline void pngChunk(FILE *file, char type[static 4], uint32_t len) {
+	pngInt32(file, len);
+	pngCRC = ~0;
+	pngWrite(file, (uint8_t *)type, 4);
+}
+
+enum {
+	PNGGrayscale,
+	PNGTruecolor = 2,
+	PNGIndexed,
+	PNGAlpha,
+};
+
+static inline void pngHead(
+	FILE *file, uint32_t width, uint32_t height, uint8_t depth, uint8_t color
+) {
+	pngWrite(file, (uint8_t *)"\x89PNG\r\n\x1A\n", 8);
+	pngChunk(file, "IHDR", 13);
+	pngInt32(file, width);
+	pngInt32(file, height);
+	pngWrite(file, &depth, 1);
+	pngWrite(file, &color, 1);
+	pngWrite(file, (uint8_t []) { 0, 0, 0 }, 3);
+	pngInt32(file, ~pngCRC);
+}
+
+static inline void pngPalette(FILE *file, const uint8_t *pal, uint32_t len) {
+	pngChunk(file, "PLTE", len);
+	pngWrite(file, pal, len);
+	pngInt32(file, ~pngCRC);
+}
+
+enum {
+	PNGNone,
+	PNGSub,
+	PNGUp,
+	PNGAverage,
+	PNGPaeth,
+};
+
+static inline void pngData(FILE *file, const uint8_t *data, uint32_t len) {
+	uint32_t adler1 = 1, adler2 = 0;
+	for (uint32_t i = 0; i < len; ++i) {
+		adler1 = (adler1 + data[i]) % 65521;
+		adler2 = (adler1 + adler2) % 65521;
+	}
+	uint32_t zlen = 2 + 5 * ((len + 0xFFFE) / 0xFFFF) + len + 4;
+	pngChunk(file, "IDAT", zlen);
+	pngWrite(file, (uint8_t []) { 0x08, 0x1D }, 2);
+	for (; len > 0xFFFF; data += 0xFFFF, len -= 0xFFFF) {
+		pngWrite(file, (uint8_t []) { 0x00, 0xFF, 0xFF, 0x00, 0x00 }, 5);
+		pngWrite(file, data, 0xFFFF);
+	}
+	pngWrite(file, (uint8_t []) { 0x01, len, len >> 8, ~len, ~len >> 8 }, 5);
+	pngWrite(file, data, len);
+	pngInt32(file, adler2 << 16 | adler1);
+	pngInt32(file, ~pngCRC);
+}
+
+static inline void pngTail(FILE *file) {
+	pngChunk(file, "IEND", 0);
+	pngInt32(file, ~pngCRC);
+}