From 4f588e9400eb82efac9c8c9fa6844419c2caa101 Mon Sep 17 00:00:00 2001
From: Michael Drake <tlsa@netsurf-browser.org>
Date: Sun, 8 May 2022 16:18:35 +0100
Subject: API: Add function to get a frame's local palette.

---
 include/nsgif.h | 20 ++++++++++++++++++++
 src/gif.c       | 25 +++++++++++++++++++++++++
 2 files changed, 45 insertions(+)

diff --git a/include/nsgif.h b/include/nsgif.h
index 9eec0f8..2251060 100644
--- a/include/nsgif.h
+++ b/include/nsgif.h
@@ -447,6 +447,26 @@ void nsgif_global_palette(
 		uint32_t table[NSGIF_MAX_COLOURS],
 		size_t *entries);
 
+/**
+ * Get the local colour palette for a frame.
+ *
+ * Frames may have no local palette. In this case they use the global palette.
+ * This function returns false if the frame has no local palette.
+ *
+ * Colours in same pixel format as \ref nsgif_bitmap_t.
+ *
+ * \param[in]  gif      The \ref nsgif_t object.
+ * \param[in]  frame    The \ref frame to get the palette for.
+ * \param[out] table    Client buffer to hold the colour table.
+ * \param[out] entries  The number of used entries in the colour table.
+ * \return true if a palette is returned, false otherwise.
+ */
+bool nsgif_local_palette(
+		const nsgif_t *gif,
+		uint32_t frame,
+		uint32_t table[NSGIF_MAX_COLOURS],
+		size_t *entries);
+
 /**
  * Configure handling of small frame delays.
  *
diff --git a/src/gif.c b/src/gif.c
index 7f960d1..09bacdc 100644
--- a/src/gif.c
+++ b/src/gif.c
@@ -1950,6 +1950,31 @@ void nsgif_global_palette(
 	*entries = gif->colour_table_size;
 }
 
+/* exported function documented in nsgif.h */
+bool nsgif_local_palette(
+		const nsgif_t *gif,
+		uint32_t frame,
+		uint32_t table[NSGIF_MAX_COLOURS],
+		size_t *entries)
+{
+	const nsgif_frame *f;
+
+	if (frame >= gif->frame_count_partial) {
+		return false;
+	}
+
+	f = &gif->frames[frame];
+	if (f->info.colour_table == false) {
+		return false;
+	}
+
+	*entries = 2 << (f->flags & NSGIF_COLOUR_TABLE_SIZE_MASK);
+	nsgif__colour_table_decode(table, &gif->colour_layout,
+			*entries, gif->buf + f->colour_table_offset);
+
+	return true;
+}
+
 /* exported function documented in nsgif.h */
 const char *nsgif_strerror(nsgif_error err)
 {
-- 
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