Refactor palette sorting computation.

This will ease the integration of new methods.

Change-Id: Icec3eddaa4ab9030d28ccfe579eb6dc13ded2f02

src/enc/vp8l_enc.c

@@ -267,7 +267,7 @@ typedef struct {
 
 // +2 because we add a palette sorting configuration for kPalette and
 // kPaletteAndSpatial.
-#define CRUNCH_CONFIGS_MAX (kNumEntropyIx + 2)
+#define CRUNCH_CONFIGS_MAX (kNumEntropyIx + 2 * kPaletteSortingNum)
 
 static int EncoderAnalyze(VP8LEncoder* const enc,
                           CrunchConfig crunch_configs[CRUNCH_CONFIGS_MAX],
@@ -324,20 +324,28 @@ static int EncoderAnalyze(VP8LEncoder* const enc,
         // a palette.
         if ((i != kPalette && i != kPaletteAndSpatial) || use_palette) {
           assert(*crunch_configs_size < CRUNCH_CONFIGS_MAX);
-          crunch_configs[(*crunch_configs_size)].entropy_idx_ = i;
           if (use_palette && (i == kPalette || i == kPaletteAndSpatial)) {
-            crunch_configs[(*crunch_configs_size)].palette_sorting_type_ =
-                kMinimizeDelta;
-            ++*crunch_configs_size;
-            // Also add modified Zeng's method.
+            for (int sorting_method = 0; sorting_method < kPaletteSortingNum;
+                 ++sorting_method) {
+              const PaletteSorting typed_sorting_method =
+                  (PaletteSorting)sorting_method;
+              // TODO(vrabaud) kSortedDefault should be tested. It is omitted
+              // for now for backward compatibility.
+              if (typed_sorting_method == kUnusedPalette ||
+                  typed_sorting_method == kSortedDefault) {
+                continue;
+              }
+              crunch_configs[(*crunch_configs_size)].entropy_idx_ = i;
+              crunch_configs[(*crunch_configs_size)].palette_sorting_type_ =
+                  typed_sorting_method;
+              ++*crunch_configs_size;
+            }
+          } else {
             crunch_configs[(*crunch_configs_size)].entropy_idx_ = i;
-            crunch_configs[(*crunch_configs_size)].palette_sorting_type_ =
-                kModifiedZeng;
-          } else {
             crunch_configs[(*crunch_configs_size)].palette_sorting_type_ =
                 kUnusedPalette;
+            ++*crunch_configs_size;
           }
-          ++*crunch_configs_size;
         }
       }
     } else {
@@ -1544,20 +1552,11 @@ static int EncodeStreamHook(void* input, void* data2) {
 
     // Encode palette
     if (enc->use_palette_) {
-      if (crunch_configs[idx].palette_sorting_type_ == kSortedDefault) {
-        // Nothing to do, we have already sorted the palette.
-        memcpy(enc->palette_, enc->palette_sorted_,
-               enc->palette_size_ * sizeof(*enc->palette_));
-      } else if (crunch_configs[idx].palette_sorting_type_ == kMinimizeDelta) {
-        PaletteSortMinimizeDeltas(enc->palette_sorted_, enc->palette_size_,
-                                  enc->palette_);
-      } else {
-        assert(crunch_configs[idx].palette_sorting_type_ == kModifiedZeng);
-        if (!PaletteSortModifiedZeng(enc->pic_, enc->palette_sorted_,
-                                     enc->palette_size_, enc->palette_)) {
-          WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
-          goto Error;
-        }
+      if (!PaletteSort(crunch_configs[idx].palette_sorting_type_, enc->pic_,
+                       enc->palette_sorted_, enc->palette_size_,
+                       enc->palette_)) {
+        WebPEncodingSetError(enc->pic_, VP8_ENC_ERROR_OUT_OF_MEMORY);
+        goto Error;
       }
       percent_range = remaining_percent / 4;
       if (!EncodePalette(bw, low_effort, enc, percent_range, &percent)) {

src/utils/palette.c

@@ -182,8 +182,8 @@ static int PaletteHasNonMonotonousDeltas(const uint32_t* const palette,
   return (sign_found & (sign_found << 1)) != 0;  // two consequent signs.
 }
 
-void PaletteSortMinimizeDeltas(const uint32_t* const palette_sorted,
-                               int num_colors, uint32_t* const palette) {
+static void PaletteSortMinimizeDeltas(const uint32_t* const palette_sorted,
+                                      int num_colors, uint32_t* const palette) {
   uint32_t predict = 0x00000000;
   int i, k;
   memcpy(palette, palette_sorted, num_colors * sizeof(*palette));
@@ -293,9 +293,10 @@ struct Sum {
   uint32_t sum;
 };
 
-int PaletteSortModifiedZeng(const WebPPicture* const pic,
-                            const uint32_t* const palette_in,
-                            uint32_t num_colors, uint32_t* const palette) {
+static int PaletteSortModifiedZeng(const WebPPicture* const pic,
+                                   const uint32_t* const palette_in,
+                                   uint32_t num_colors,
+                                   uint32_t* const palette) {
   uint32_t i, j, ind;
   uint8_t remapping[MAX_PALETTE_SIZE];
   uint32_t* cooccurrence;
@@ -375,3 +376,27 @@ int PaletteSortModifiedZeng(const WebPPicture* const pic,
   }
   return 1;
 }
+
+// -----------------------------------------------------------------------------
+
+int PaletteSort(PaletteSorting method, const struct WebPPicture* const pic,
+                const uint32_t* const palette_sorted, uint32_t num_colors,
+                uint32_t* const palette) {
+  switch (method) {
+    case kSortedDefault:
+      // Nothing to do, we have already sorted the palette.
+      memcpy(palette, palette_sorted, num_colors * sizeof(*palette));
+      return 1;
+    case kMinimizeDelta:
+      PaletteSortMinimizeDeltas(palette_sorted, num_colors, palette);
+      return 1;
+    case kModifiedZeng:
+      return PaletteSortModifiedZeng(pic, palette_sorted, num_colors, palette);
+    case kUnusedPalette:
+    case kPaletteSortingNum:
+      break;
+  }
+
+  assert(0);
+  return 0;
+}

src/utils/palette.h

@@ -21,9 +21,15 @@ struct WebPPicture;
 // The different ways a palette can be sorted.
 typedef enum PaletteSorting {
   kSortedDefault = 0,
+  // Sorts by minimizing L1 deltas between consecutive colors, giving more
+  // weight to RGB colors.
   kMinimizeDelta = 1,
+  // Implements the modified Zeng method from "A Survey on Palette Reordering
+  // Methods for Improving the Compression of Color-Indexed Images" by Armando
+  // J. Pinho and Antonio J. R. Neves.
   kModifiedZeng = 2,
-  kUnusedPalette = 3
+  kUnusedPalette = 3,
+  kPaletteSortingNum = 4
 } PaletteSorting;
 
 // Returns the index of 'color' in the sorted palette 'sorted' of size
@@ -44,19 +50,11 @@ void PrepareMapToPalette(const uint32_t palette[], uint32_t num_colors,
 int GetColorPalette(const struct WebPPicture* const pic,
                     uint32_t* const palette);
 
-// Sorts the color sorted palette in 'palette_sorted'/'num_colors' by
-// minimizing deltas between consecutive colors and stores it in 'palette'.
-void PaletteSortMinimizeDeltas(const uint32_t* const palette_sorted,
-                               int num_colors, uint32_t* const palette);
-
-// Implements the modified Zeng method from "A Survey on Palette Reordering
-// Methods for Improving the Compression of Color-Indexed Images" by Armando J.
-// Pinho and Antonio J. R. Neves. The palette defined by 'palette_in' and
-// 'num_colors' is sorted using information from 'pic' and output in
-// 'palette'.
-// Returns 0 on memory allocation error.
-int PaletteSortModifiedZeng(const struct WebPPicture* const pic,
-                            const uint32_t* const palette_in,
-                            uint32_t num_colors, uint32_t* const palette);
+// Sorts the palette according to the criterion defined by 'method'.
+// 'palette_sorted' is the input palette sorted lexicographically, as done in
+// PrepareMapToPalette. Returns 0 on memory allocation error.
+int PaletteSort(PaletteSorting method, const struct WebPPicture* pic,
+                const uint32_t* palette_sorted, uint32_t num_colors,
+                uint32_t* palette);
 
 #endif  // WEBP_UTILS_PALETTE_H_