Add some functions needed fore encoding LSS16 files

Signed-off-by: Mattias Andrée <m@maandree.se>

1 files changed, 80 insertions, 0 deletions

diff --git a/liblss16_optimise.c b/liblss16_optimise.c
new file mode 100644
index 0000000..911fcd2
--- /dev/null
+++ b/liblss16_optimise.c
@@ -0,0 +1,80 @@
+/* See LICENSE file for copyright and license details. */
+#include "liblss16.h"
+#include <string.h>
+
+
+void
+liblss16_optimise(struct liblss16_header *header, uint8_t *pixels)
+{
+	uint8_t remap[16], unmap[16], ncolours, colour, preferred;
+	unsigned x, y, count, width;
+	size_t p, n;
+	int32_t zero[16], nonzero[16];
+	int32_t zero_penalty, least;
+
+	for (x = 0; x < 16U; x++) {
+		remap[x] = (uint8_t)x;
+		unmap[x] = 0;
+	}
+
+	memset(zero, 0, sizeof(zero));
+	memset(nonzero, 0, sizeof(nonzero));
+
+	for (x = 0; x < 15U; x++) {
+		if (unmap[x])
+			continue;
+		header->colour_map[ncolours++] = header->colour_map[x];
+		for (y = x + 1U; y < 16U; y++) {
+			if (header->colour_map[y].r != header->colour_map[x].r ||
+			    header->colour_map[y].g != header->colour_map[x].g ||
+			    header->colour_map[y].b != header->colour_map[x].b)
+				continue;
+			unmap[y] = 1;
+			remap[y] = ncolours;
+		}
+	}
+
+	width = (unsigned)header->width;
+	width = width < 17U ? width : 17U;
+	for (y = 0, p = 0; y < (unsigned)header->height; y++) {
+		colour = remap[pixels[p]];
+		count = 1U;
+		for (x = 1U; x < width; x++, p++) {
+			if (remap[pixels[p]] != colour)
+				break;
+			count += 1U;
+		}
+		p += (size_t)header->width - (size_t)x;
+		zero[colour] += count < 16U ? 2 : 3;
+		nonzero[colour] += count == 1 ? 1 : count < 17 ? 3 : 4;
+	}
+
+	least = zero[0] - nonzero[0];
+	preferred = 0U;
+	for (x = 1U; x < (unsigned)ncolours; x++) {
+		zero_penalty = zero[x] - nonzero[x];
+		if (zero_penalty < least) {
+			least = zero_penalty;
+			preferred = (uint8_t)x;
+		}
+	}
+
+	if (preferred) {
+		struct liblss16_colour tc;
+		uint8_t t8;
+		tc = header->colour_map[preferred];
+		header->colour_map[preferred] = header->colour_map[0];
+		header->colour_map[0] = tc;
+		t8 = remap[preferred];
+		remap[preferred] = remap[0];
+		remap[0] = t8;
+	}
+
+	n = p;
+	for (n = p, p = 0; p < n; p++)
+		pixels[p] = remap[pixels[p]];
+
+	memset(&header->colour_map[ncolours],
+	       header->colour_map[ncolours - 1U].b,
+	       (16U - ncolours) * sizeof(*header->colour_map));
+}