Add RLE encoding support, patch by Bobby Bingham, uhmmmm gmail com.

Originally committed as revision 8434 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/targaenc.c

@@ -21,6 +21,86 @@
  */
 #include "avcodec.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(uint8_t *start, int len, int bpp, int same)
+{
+    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 image, with maximum size of out_size
+ * @param outbuf Output buffer
+ * @param out_size Maximum output size
+ * @param pic Image to compress
+ * @param bpp Bytes per pixel
+ * @param w Image width
+ * @param h Image height
+ * @return Size of output in bytes, or -1 if larger than out_size
+ */
+static int targa_encode_rle(uint8_t *outbuf, int out_size, AVFrame *pic,
+                            int bpp, int w, int h)
+{
+    int count, x, y;
+    uint8_t *ptr, *line, *out;
+
+    out = outbuf;
+    line = pic->data[0];
+
+    for(y = 0; y < h; y ++) {
+        ptr = line;
+
+        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++ = 0x80 | (count - 1);
+                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;
+        }
+
+        line += pic->linesize[0];
+    }
+
+    return out - outbuf;
+}
+
 static int targa_encode_normal(uint8_t *outbuf, AVFrame *pic, int bpp, int w, int h)
 {
     int i, n = bpp * w;
@@ -40,14 +120,15 @@ static int targa_encode_frame(AVCodecContext *avctx,
                               unsigned char *outbuf,
                               int buf_size, void *data){
     AVFrame *p = data;
-    int bpp;
+    int bpp, picsize, datasize;
     uint8_t *out;
 
     if(avctx->width > 0xffff || avctx->height > 0xffff) {
         av_log(avctx, AV_LOG_ERROR, "image dimensions too large\n");
         return -1;
     }
-    if(buf_size < avpicture_get_size(avctx->pix_fmt, avctx->width, avctx->height) + 45) {
+    picsize = avpicture_get_size(avctx->pix_fmt, avctx->width, avctx->height);
+    if(buf_size < picsize + 45) {
         av_log(avctx, AV_LOG_ERROR, "encoded frame too large\n");
         return -1;
     }
@@ -61,7 +142,7 @@ static int targa_encode_frame(AVCodecContext *avctx,
     AV_WL16(outbuf+14, avctx->height);
     outbuf[17] = 0x20;           /* origin is top-left. no alpha */
 
-    /* TODO: support alpha channel and RLE */
+    /* TODO: support alpha channel */
     switch(avctx->pix_fmt) {
     case PIX_FMT_GRAY8:
         outbuf[2] = 3;           /* uncompressed grayscale image */
@@ -82,7 +163,17 @@ static int targa_encode_frame(AVCodecContext *avctx,
 
     out = outbuf + 18;  /* skip past the header we just output */
 
-    out += targa_encode_normal(out, p, bpp, avctx->width, avctx->height);
+    /* try RLE compression */
+    datasize = targa_encode_rle(out, picsize, p, bpp, avctx->width, avctx->height);
+
+    /* if that worked well, mark the picture as RLE compressed */
+    if(datasize >= 0)
+        outbuf[2] |= 8;
+
+    /* if RLE didn't make it smaller, go back to no compression */
+    else datasize = targa_encode_normal(out, p, bpp, avctx->width, avctx->height);
+
+    out += datasize;
 
     /* The standard recommends including this section, even if we don't use
      * any of the features it affords. TODO: take advantage of the pixel