Implement basic ASTC support

Implements basic ASTC support:
* Only 4x4 and 8x8 block sizes.
* Other block sizes are too complex to handle for Godot image compression handling. May be implemented sometime in the future.

The need for ASTC is mostly for the following use cases:
* Implement a high quality compression option for textures on mobile and M1 Apple hardware.
* For this, the 4x4 is sufficient, since it uses the same size as BPTC.

ASTC supports a lot of block sizes, but the benefit of supporting most of them is slim, while the implementation complexity in Godot is very high.
Supporting only 4x4 (and 8x8) solves the real problem, which is lack of a BPTC alternative on hardware where it's missing.

Note: This does not yet support encoding on import, an ASTC encoder will need to be added.

1 files changed, 15 insertions, 2 deletions

diff --git a/core/io/image.h b/core/io/image.h
index fd264a7a38..0e37e78c76 100644
--- a/core/io/image.h
+++ b/core/io/image.h
@@ -109,6 +109,10 @@ public:
 		FORMAT_ETC2_RGB8A1,
 		FORMAT_ETC2_RA_AS_RG, //used to make basis universal happy
 		FORMAT_DXT5_RA_AS_RG, //used to make basis universal happy
+		FORMAT_ASTC_4x4,
+		FORMAT_ASTC_4x4_HDR,
+		FORMAT_ASTC_8x8,
+		FORMAT_ASTC_8x8_HDR,
 		FORMAT_MAX
 	};
 
@@ -134,6 +138,11 @@ public:
 	};
 	//some functions provided by something else
 
+	enum ASTCFormat {
+		ASTC_FORMAT_4x4,
+		ASTC_FORMAT_8x8,
+	};
+
 	static ImageMemLoadFunc _png_mem_loader_func;
 	static ImageMemLoadFunc _jpg_mem_loader_func;
 	static ImageMemLoadFunc _webp_mem_loader_func;
@@ -144,11 +153,13 @@ public:
 	static void (*_image_compress_bptc_func)(Image *, float p_lossy_quality, UsedChannels p_channels);
 	static void (*_image_compress_etc1_func)(Image *, float);
 	static void (*_image_compress_etc2_func)(Image *, float, UsedChannels p_channels);
+	static void (*_image_compress_astc_func)(Image *, float, ASTCFormat p_format);
 
 	static void (*_image_decompress_bc)(Image *);
 	static void (*_image_decompress_bptc)(Image *);
 	static void (*_image_decompress_etc1)(Image *);
 	static void (*_image_decompress_etc2)(Image *);
+	static void (*_image_decompress_astc)(Image *);
 
 	static Vector<uint8_t> (*webp_lossy_packer)(const Ref<Image> &p_image, float p_quality);
 	static Vector<uint8_t> (*webp_lossless_packer)(const Ref<Image> &p_image);
@@ -351,6 +362,7 @@ public:
 		COMPRESS_ETC,
 		COMPRESS_ETC2,
 		COMPRESS_BPTC,
+		COMPRESS_ASTC,
 		COMPRESS_MAX,
 	};
 	enum CompressSource {
@@ -360,8 +372,8 @@ public:
 		COMPRESS_SOURCE_MAX,
 	};
 
-	Error compress(CompressMode p_mode, CompressSource p_source = COMPRESS_SOURCE_GENERIC, float p_lossy_quality = 0.7);
-	Error compress_from_channels(CompressMode p_mode, UsedChannels p_channels, float p_lossy_quality = 0.7);
+	Error compress(CompressMode p_mode, CompressSource p_source = COMPRESS_SOURCE_GENERIC, float p_lossy_quality = 0.7, ASTCFormat p_astc_format = ASTC_FORMAT_4x4);
+	Error compress_from_channels(CompressMode p_mode, UsedChannels p_channels, float p_lossy_quality = 0.7, ASTCFormat p_astc_format = ASTC_FORMAT_4x4);
 	Error decompress();
 	bool is_compressed() const;
 
@@ -432,5 +444,6 @@ VARIANT_ENUM_CAST(Image::CompressSource)
 VARIANT_ENUM_CAST(Image::UsedChannels)
 VARIANT_ENUM_CAST(Image::AlphaMode)
 VARIANT_ENUM_CAST(Image::RoughnessChannel)
+VARIANT_ENUM_CAST(Image::ASTCFormat)
 
 #endif // IMAGE_H