Have the palette code be in its own file.

Change-Id: I099a342effedd9f451c94d00a14aead27079e6cc

src/utils/palette.h

@@ -0,0 +1,62 @@
+// Copyright 2023 Google Inc. All Rights Reserved.
+//
+// Use of this source code is governed by a BSD-style license
+// that can be found in the COPYING file in the root of the source
+// tree. An additional intellectual property rights grant can be found
+// in the file PATENTS. All contributing project authors may
+// be found in the AUTHORS file in the root of the source tree.
+// -----------------------------------------------------------------------------
+//
+// Utilities for palette analysis.
+//
+// Author: Vincent Rabaud (vrabaud@google.com)
+
+#ifndef WEBP_UTILS_PALETTE_H_
+#define WEBP_UTILS_PALETTE_H_
+
+#include "src/webp/types.h"
+
+struct WebPPicture;
+
+// The different ways a palette can be sorted.
+typedef enum PaletteSorting {
+  kSortedDefault = 0,
+  kMinimizeDelta = 1,
+  kModifiedZeng = 2,
+  kUnusedPalette = 3
+} PaletteSorting;
+
+// Returns the index of 'color' in the sorted palette 'sorted' of size
+// 'num_colors'.
+int SearchColorNoIdx(const uint32_t sorted[], uint32_t color, int num_colors);
+
+// Sort palette in increasing order and prepare an inverse mapping array.
+void PrepareMapToPalette(const uint32_t palette[], uint32_t num_colors,
+                         uint32_t sorted[], uint32_t idx_map[]);
+
+// Returns count of unique colors in 'pic', assuming pic->use_argb is true.
+// If the unique color count is more than MAX_PALETTE_SIZE, returns
+// MAX_PALETTE_SIZE+1.
+// If 'palette' is not NULL and the number of unique colors is less than or
+// equal to MAX_PALETTE_SIZE, also outputs the actual unique colors into
+// 'palette' in a sorted order. Note: 'palette' is assumed to be an array
+// already allocated with at least MAX_PALETTE_SIZE elements.
+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);
+
+#endif  // WEBP_UTILS_PALETTE_H_