1 /*
2  * Copyright (C) 2009 The Android Open Source Project
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  *      http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 
17 package android.opengl;
18 
19 import java.nio.Buffer;
20 
21 /**
22  * Methods for encoding and decoding ETC1 textures.
23  * <p>
24  * The standard for the ETC1 texture format can be found at
25  * http://www.khronos.org/registry/gles/extensions/OES/OES_compressed_ETC1_RGB8_texture.txt
26  * <p>
27  * The PKM file format is of a 16-byte header that describes the image bounds
28  * followed by the encoded ETC1 texture data.
29  * <p>
30  * @see ETC1Util
31  */
32 public class ETC1 {
33 
34     /**
35      * Size in bytes of an encoded block.
36      */
37     public static final int ENCODED_BLOCK_SIZE = 8;
38 
39     /**
40      * Size in bytes of a decoded block.
41      */
42     public static final int DECODED_BLOCK_SIZE = 48;
43 
44     /**
45      * Size of a PKM file header, in bytes.
46      */
47     public static final int ETC_PKM_HEADER_SIZE = 16;
48 
49     /**
50      * Accepted by the internalformat parameter of glCompressedTexImage2D.
51      */
52     public static final int ETC1_RGB8_OES = 0x8D64;
53 
54     /**
55      * Encode a block of pixels.
56      *
57      * @param in a native order direct buffer of size DECODED_BLOCK_SIZE that represent a
58      * 4 x 4 square of 3-byte pixels in form R, G, B. Byte (3 * (x + 4 * y) is the R
59      * value of pixel (x, y).
60      *
61      * @param validPixelMask is a 16-bit mask where bit (1 << (x + y * 4)) indicates whether
62      * the corresponding (x,y) pixel is valid. Invalid pixel color values are ignored when compressing.
63      *
64      * @param out a native order direct buffer of size ENCODED_BLOCK_SIZE that receives the
65      * ETC1 compressed version of the data.
66      *
67      */
encodeBlock(Buffer in, int validPixelMask, Buffer out)68     public static native void encodeBlock(Buffer in, int validPixelMask, Buffer out);
69 
70     /**
71      * Decode a block of pixels.
72      *
73      * @param in a native order direct buffer of size ENCODED_BLOCK_SIZE that contains the
74      * ETC1 compressed version of the data.
75      *
76      * @param out a native order direct buffer of size DECODED_BLOCK_SIZE that will receive
77      * the decoded data. The data represents a
78      * 4 x 4 square of 3-byte pixels in form R, G, B. Byte (3 * (x + 4 * y) is the R
79      * value of pixel (x, y).
80      */
decodeBlock(Buffer in, Buffer out)81     public static native void decodeBlock(Buffer in, Buffer out);
82 
83     /**
84      * Return the size of the encoded image data (does not include size of PKM header).
85      */
getEncodedDataSize(int width, int height)86     public static native int getEncodedDataSize(int width, int height);
87 
88     /**
89      * Encode an entire image.
90      * @param in a native order direct buffer of the image data. Formatted such that
91      *           pixel (x,y) is at pIn + pixelSize * x + stride * y;
92      * @param out a native order direct buffer of the encoded data.
93      * Must be large enough to store entire encoded image.
94      * @param pixelSize must be 2 or 3. 2 is an GL_UNSIGNED_SHORT_5_6_5 image,
95      * 3 is a GL_BYTE RGB image.
96      */
encodeImage(Buffer in, int width, int height, int pixelSize, int stride, Buffer out)97     public static native void encodeImage(Buffer in, int width, int height,
98             int pixelSize, int stride, Buffer out);
99 
100     /**
101      * Decode an entire image.
102      * @param in native order direct buffer of the encoded data.
103      * @param out native order direct buffer of the image data. Will be written such that
104      * pixel (x,y) is at pIn + pixelSize * x + stride * y. Must be
105      * large enough to store entire image.
106      * @param pixelSize must be 2 or 3. 2 is an GL_UNSIGNED_SHORT_5_6_5 image,
107      * 3 is a GL_BYTE RGB image.
108      */
decodeImage(Buffer in, Buffer out, int width, int height, int pixelSize, int stride)109     public static native void decodeImage(Buffer in, Buffer out,
110             int width, int height, int pixelSize, int stride);
111 
112     /**
113      * Format a PKM header
114      * @param header native order direct buffer of the header.
115      * @param width the width of the image in pixels.
116      * @param height the height of the image in pixels.
117      */
formatHeader(Buffer header, int width, int height)118     public static native void formatHeader(Buffer header, int width, int height);
119 
120     /**
121      * Check if a PKM header is correctly formatted.
122      * @param header native order direct buffer of the header.
123      */
isValid(Buffer header)124     public static native boolean isValid(Buffer header);
125 
126     /**
127      * Read the image width from a PKM header
128      * @param header native order direct buffer of the header.
129      */
getWidth(Buffer header)130     public static native int getWidth(Buffer header);
131 
132     /**
133      * Read the image height from a PKM header
134      * @param header native order direct buffer of the header.
135      */
getHeight(Buffer header)136     public static native int getHeight(Buffer header);
137 }
138