generic rle encoder by Bartlomiej Wolowiec b.wolowiec students mimuw edu pl

Originally committed as revision 8598 to svn://svn.ffmpeg.org/ffmpeg/trunk

1 files changed, 96 insertions, 0 deletions

diff --git a/libavcodec/rle.c b/libavcodec/rle.c
new file mode 100644
index 0000000000..aa05f6d513
--- /dev/null
+++ b/libavcodec/rle.c
@@ -0,0 +1,96 @@
+/*
+ * RLE encoder
+ * Copyright (c) 2007 Bobby Bingham
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg 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
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ *
+ */
+#include "avcodec.h"
+#include "rle.h"
+
+/**
+ * Count up to 127 consecutive pixels which are either all the same or
+ * all differ from the previous and next pixels.
+ * @param start Pointer to the first pixel
+ * @param len Maximum number of pixels
+ * @param bpp Bytes per pixel
+ * @param same 1 if searching for identical pixel values.  0 for differing
+ * @return Number of matching consecutive pixels found
+ */
+static int count_pixels(const uint8_t *start, int len, int bpp, int same)
+{
+    const uint8_t *pos;
+    int count = 1;
+
+    for(pos = start + bpp; count < FFMIN(128, len); pos += bpp, count ++) {
+        if(same != !memcmp(pos-bpp, pos, bpp)) {
+            if(!same) {
+                /* if bpp == 1, then 0 1 1 0 is more efficiently encoded as a single
+                 * raw block of pixels.  for larger bpp, RLE is as good or better */
+                if(bpp == 1 && count + 1 < FFMIN(128, len) && *pos != *(pos+1))
+                    continue;
+
+                /* if RLE can encode the next block better than as a raw block,
+                 * back up and leave _all_ the identical pixels for RLE */
+                count --;
+            }
+            break;
+        }
+    }
+
+    return count;
+}
+
+/**
+ * RLE compress the row, with maximum size of out_size. Value before repeated bytes is (count ^ xor) + add.
+ * @param outbuf Output buffer
+ * @param out_size Maximum output size
+ * @param ptr Input buffer
+ * @param bpp Bytes per pixel
+ * @param w Image width
+ * @return Size of output in bytes, or -1 if larger than out_size
+ */
+int ff_rle_encode(uint8_t *outbuf, int out_size, const uint8_t *ptr , int bpp, int w, int8_t add, uint8_t xor)
+{
+    int count, x;
+    uint8_t *out;
+
+    out = outbuf;
+
+
+        for(x = 0; x < w; x += count) {
+            /* see if we can encode the next set of pixels with RLE */
+            if((count = count_pixels(ptr, w-x, bpp, 1)) > 1) {
+                if(out + bpp + 1 > outbuf + out_size) return -1;
+                *out++ = (count ^ xor) + add;
+                memcpy(out, ptr, bpp);
+                out += bpp;
+            } else {
+                /* fall back on uncompressed */
+                count = count_pixels(ptr, w-x, bpp, 0);
+                *out++ = count - 1;
+
+                if(out + bpp*count > outbuf + out_size) return -1;
+                memcpy(out, ptr, bpp * count);
+                out += bpp * count;
+        }
+
+        ptr += count * bpp;
+    }
+
+    return out - outbuf;
+}