1 files changed, 68 insertions, 0 deletions
diff --git a/bmp.cpp b/bmp.cpp
new file mode 100644
index 0000000..329049c
--- /dev/null
+++ b/bmp.cpp
@@ -0,0 +1,68 @@
+#include <cstdio>
+#include <cassert>
+#include "bmp.h"
+
+
+int64_t bmp_rgb_encoded_size(int width, int height) {
+	return 54 + (3 * (int64_t)width + 3) / 4 * 4 * (int64_t)height;
+}
+
+static void write_le32(uint8_t *dst, uint32_t value) {
+	dst[0] = value & 0xff;
+	dst[1] = (value >> 8) & 0xff;
+	dst[2] = (value >> 16) & 0xff;
+	dst[3] = value >> 24;
+}
+
+static void write_le16(uint8_t *dst, uint16_t value) {
+	dst[0] = value & 0xff;
+	dst[1] = value >> 8;
+}
+
+void bmp_rgb_encode_memory(uint8_t *dst, const uint8_t *src, int width, int height) {
+	const int64_t size = bmp_rgb_encoded_size(width, height);
+	const int padding = (4 - 3 * width % 4) % 4;
+	dst[0] = 'B';
+	dst[1] = 'M';
+	write_le32(&dst[2], size);
+	dst[6] = dst[7] = dst[8] = dst[9] = 0;
+	write_le32(&dst[10], 54);
+	write_le32(&dst[14], 40);  // this is a BITMAPINFOHEADER
+	write_le32(&dst[18], width);
+	write_le32(&dst[22], height);
+	write_le16(&dst[26], 1);
+	write_le16(&dst[28], 24);
+	write_le32(&dst[30], 0);
+	write_le32(&dst[34], size - 54);
+	write_le32(&dst[38], 0);  // pixels/metre; imagemagick sets this to 0
+	write_le32(&dst[42], 0);  // and if they can, we can
+	write_le32(&dst[46], 0);
+	write_le32(&dst[50], 0);
+	int off = 54;
+	for (int y = height - 1; y >= 0; y--) {
+		for (int x = 0; x < width; x++) {
+			dst[off+0] = src[3 * (width * y + x) + 2];
+			dst[off+1] = src[3 * (width * y + x) + 1];
+			dst[off+2] = src[3 * (width * y + x) + 0];
+			off += 3;
+		}
+		for (int i = 0; i < padding; i++) dst[off++] = 0;
+	}
+	assert(off == size);
+}
+
+uint8_t* bmp_rgb_encode_memory_alloc(const uint8_t *src, int width, int height) {
+	const int64_t size = bmp_rgb_encoded_size(width, height);
+	uint8_t *dst = new uint8_t[size];
+	bmp_rgb_encode_memory(dst, src, width, height);
+	return dst;
+}
+
+void bmp_rgb_encode_file(const char *fname, const uint8_t *src, int width, int height) {
+	const int64_t size = bmp_rgb_encoded_size(width, height);
+	uint8_t *data = bmp_rgb_encode_memory_alloc(src, width, height);
+	FILE *f = fopen(fname, "w");
+	fwrite(data, 1, size, f);
+	fclose(f);
+	delete[] data;
+}