1/*
2 * Copyright 2012 Google Inc.
3 *
4 * Use of this source code is governed by a BSD-style license that can be
5 * found in the LICENSE file.
6 */
7
8#include "SkBitmap.h"
9#include "SkBitmapHasher.h"
10#include "SkEndian.h"
11#include "SkImageEncoder.h"
12
13#include "SkMD5.h"
14
15/**
16 * Write an int32 value to a stream in little-endian order.
17 */
18static void write_int32_to_buffer(uint32_t val, SkWStream* out) {
19    val = SkEndian_SwapLE32(val);
20    for (size_t byte = 0; byte < 4; ++byte) {
21        out->write8((uint8_t)(val & 0xff));
22        val = val >> 8;
23    }
24}
25
26/**
27 * Return the first 8 bytes of a bytearray, encoded as a little-endian uint64.
28 */
29static inline uint64_t first_8_bytes_as_uint64(const uint8_t *bytearray) {
30    return SkEndian_SwapLE64(*(reinterpret_cast<const uint64_t *>(bytearray)));
31}
32
33/*static*/ bool SkBitmapHasher::ComputeDigestInternal(const SkBitmap& bitmap, uint64_t *result) {
34    SkMD5 out;
35
36    // start with the x/y dimensions
37    write_int32_to_buffer(SkToU32(bitmap.width()), &out);
38    write_int32_to_buffer(SkToU32(bitmap.height()), &out);
39
40    // add all the pixel data
41    SkAutoTDelete<SkImageEncoder> enc(CreateARGBImageEncoder());
42    if (!enc->encodeStream(&out, bitmap, SkImageEncoder::kDefaultQuality)) {
43        return false;
44    }
45
46    SkMD5::Digest digest;
47    out.finish(digest);
48    *result = first_8_bytes_as_uint64(digest.data);
49    return true;
50}
51
52/*static*/ bool SkBitmapHasher::ComputeDigest(const SkBitmap& bitmap, uint64_t *result) {
53    if (ComputeDigestInternal(bitmap, result)) {
54        return true;
55    }
56
57    // Hmm, that didn't work. Maybe if we create a new
58    // version of the bitmap it will work better?
59    SkBitmap copyBitmap;
60    if (!bitmap.copyTo(&copyBitmap, kN32_SkColorType)) {
61        return false;
62    }
63    return ComputeDigestInternal(copyBitmap, result);
64}
65