From b60869a18efc95ca9b6e09b5137eba6a1c250520 Mon Sep 17 00:00:00 2001
From: James Zern <jzern@google.com>
Date: Fri, 21 May 2021 10:23:05 -0700
Subject: [PATCH] Revert "Do not use a palette for one color images."

This reverts commit b6513fbaa8a3e21d1d726f6c63bbfa76f157b9a2.

This change can produce files that can cause decode failures in some
versions of chrome and safari/ios/macos.

https://chromium-review.googlesource.com/c/chromium/src/+/2876279

The chrome fix will be available in M92. This change can be revisited
after it and the mac updates are more widely deployed.

Bug: b/186640109,b/188702956
Change-Id: I296b8fe88c6c48219e3edf532226c4f972f1605b
---
 src/enc/backward_references_enc.c | 22 ----------------------
 src/enc/backward_references_enc.h |  5 +----
 src/enc/vp8l_enc.c                | 13 -------------
 3 files changed, 1 insertion(+), 39 deletions(-)

diff --git a/src/enc/backward_references_enc.c b/src/enc/backward_references_enc.c
index d99fb8ba..519b36a0 100644
--- a/src/enc/backward_references_enc.c
+++ b/src/enc/backward_references_enc.c
@@ -550,25 +550,6 @@ static int BackwardReferencesLz77(int xsize, int ysize,
   return ok;
 }
 
-static int BackwardReferencesNone(int xsize, int ysize,
-                                  const uint32_t* const argb, int cache_bits,
-                                  VP8LBackwardRefs* const refs) {
-  const int pix_count = xsize * ysize;
-  int i;
-  const int use_color_cache = (cache_bits > 0);
-  VP8LColorCache hashers;
-
-  if (use_color_cache && !VP8LColorCacheInit(&hashers, cache_bits)) {
-    return 0;
-  }
-  VP8LClearBackwardRefs(refs);
-  for (i = 0; i < pix_count; ++i) {
-    AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
-  }
-  if (use_color_cache) VP8LColorCacheClear(&hashers);
-  return !refs->error_;
-}
-
 // Compute an LZ77 by forcing matches to happen within a given distance cost.
 // We therefore limit the algorithm to the lowest 32 values in the PlaneCode
 // definition.
@@ -938,9 +919,6 @@ static int GetBackwardReferences(int width, int height,
         res = BackwardReferencesLz77Box(width, height, argb, 0, hash_chain,
                                         &hash_chain_box, refs_tmp);
         break;
-      case kLZ77None:
-        res = BackwardReferencesNone(width, height, argb, 0, refs_tmp);
-        break;
       default:
         assert(0);
     }
diff --git a/src/enc/backward_references_enc.h b/src/enc/backward_references_enc.h
index 5c901df2..4c0267b4 100644
--- a/src/enc/backward_references_enc.h
+++ b/src/enc/backward_references_enc.h
@@ -213,10 +213,7 @@ static WEBP_INLINE void VP8LRefsCursorNext(VP8LRefsCursor* const c) {
 enum VP8LLZ77Type {
   kLZ77Standard = 1,
   kLZ77RLE = 2,
-  kLZ77Box = 4,
-  // With kLZ77None, LZ77 is not even tried. For now, this is only useful for
-  // 1-color images but we could use it if we are sure the image is a photo.
-  kLZ77None = 8
+  kLZ77Box = 4
 };
 
 // Evaluates best possible backward references for specified quality.
diff --git a/src/enc/vp8l_enc.c b/src/enc/vp8l_enc.c
index 9ed6ea2a..e330e716 100644
--- a/src/enc/vp8l_enc.c
+++ b/src/enc/vp8l_enc.c
@@ -591,19 +591,6 @@ static int EncoderAnalyze(VP8LEncoder* const enc,
           sizeof(*enc->palette_sorted_), PaletteCompareColorsForQsort);
   }
 
-  if (use_palette && enc->palette_size_ == 1) {
-    crunch_configs[0].entropy_idx_ = kDirect;
-    crunch_configs[0].sub_configs_size_ = 1;
-    crunch_configs[0].sub_configs_[0].lz77_ = kLZ77None;
-    crunch_configs[0].sub_configs_[0].do_no_cache_ = 1;
-    *crunch_configs_size = 1;
-    // Get the entropy image as small as possible.
-    enc->histo_bits_ = MAX_HUFFMAN_BITS;
-    // The transform image is unused as we are direct.
-    enc->transform_bits_ = MAX_TRANSFORM_BITS;
-    return 1;
-  }
-
   // Empirical bit sizes.
   enc->histo_bits_ = GetHistoBits(method, use_palette,
                                   pic->width, pic->height);