Support KTX on big-endian systems

Author: solidpixel

Source/astcenccli_image_load_store.cpp

@@ -34,6 +34,18 @@
 #include "ThirdParty/stb_image_write.h"
 #include "ThirdParty/tinyexr.h"
 
+/**
+ * @brief Reverse the bytes in a uint32_t value.
+ */
+static uint32_t reverse_bytes_u32(
+	uint32_t val
+) {
+	return ((val >> 24) & 0x000000FF) |
+	       ((val >>  8) & 0x0000FF00) |
+	       ((val <<  8) & 0x00FF0000) |
+	       ((val << 24) & 0xFF000000);
+}
+
 /**
  * @brief Determine the output file name to use for a sliced image write.
  *
@@ -656,18 +668,6 @@ static void switch_endianness4(
 	}
 }
 
-/**
- * @brief Swap endianness of a u32 value.
- *
- * @param v   The data to convert.
- *
- * @return The converted value.
- */
-static uint32_t u32_byterev(uint32_t v)
-{
-	return (v >> 24) | ((v >> 8) & 0xFF00) | ((v << 8) & 0xFF0000) | (v << 24);
-}
-
 /*
  Notes about KTX:
 
@@ -904,7 +904,7 @@ static uint8_t ktx_magic[12] {
 
 static void ktx_header_switch_endianness(ktx_header * kt)
 {
-	#define REV(x) kt->x = u32_byterev(kt->x)
+	#define REV(x) kt->x = reverse_bytes_u32(kt->x)
 	REV(endianness);
 	REV(gl_type);
 	REV(gl_type_size);
@@ -961,11 +961,11 @@ static astcenc_image* load_ktx_uncompressed_image(
 		return nullptr;
 	}
 
-	int switch_endianness = 0;
+	bool switch_endianness = false;
 	if (hdr.endianness == 0x01020304)
 	{
 		ktx_header_switch_endianness(&hdr);
-		switch_endianness = 1;
+		switch_endianness = true;
 	}
 
 	if (hdr.gl_type == 0 || hdr.gl_format == 0)
@@ -1191,7 +1191,7 @@ static astcenc_image* load_ktx_uncompressed_image(
 
 	if (switch_endianness)
 	{
-		specified_bytes_of_surface = u32_byterev(specified_bytes_of_surface);
+		specified_bytes_of_surface = reverse_bytes_u32(specified_bytes_of_surface);
 	}
 
 	// read the surface
@@ -1346,7 +1346,7 @@ bool load_ktx_compressed_image(
 
 	if (switch_endianness)
 	{
-		data_len = u32_byterev(data_len);
+		data_len = reverse_bytes_u32(data_len);
 	}
 
 	// Read the data
@@ -1409,6 +1409,10 @@ bool store_ktx_compressed_image(
 	hdr.number_of_mipmap_levels = 1;
 	hdr.bytes_of_key_value_data = 0;
 
+#if defined(ASTCENC_BIG_ENDIAN)
+	ktx_header_switch_endianness(&hdr);
+#endif
+
 	size_t expected = sizeof(ktx_header) + 4 + img.data_len;
 	size_t actual = 0;
 
@@ -1418,8 +1422,13 @@ bool store_ktx_compressed_image(
 		return true;
 	}
 
+	uint32_t data_len = static_cast<uint32_t>(img.data_len);
+#if defined(ASTCENC_BIG_ENDIAN)
+	data_len = reverse_bytes_u32(data_len);
+#endif
+
 	actual += fwrite(&hdr, 1, sizeof(ktx_header), wf);
-	actual += fwrite(&img.data_len, 1, 4, wf);
+	actual += fwrite(&data_len, 1, sizeof(uint32_t), wf);
 	actual += fwrite(img.data, 1, img.data_len, wf);
 	fclose(wf);
 
@@ -1746,21 +1755,6 @@ struct dds_header_dx10
 #define DDS_MAGIC 0x20534444
 #define DX10_MAGIC 0x30315844
 
-
-#if defined(ASTCENC_BIG_ENDIAN)
-/**
- * @brief Reverse the bytes in a uint32_t value.
- */
-static uint32_t reverse_bytes_u32(
-	uint32_t val
-) {
-	return ((val >> 24) & 0x000000FF) |
-	       ((val >>  8) & 0x0000FF00) |
-		   ((val <<  8) & 0x00FF0000) |
-		   ((val << 24) & 0xFF000000);
-}
-#endif
-
 /**
  * @brief Load an uncompressed DDS image using the local custom loader.
  *