SkJpegCodec

src/codec/SkJpegUtility.cpp

+/*
+ * Copyright 2015 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkCodecPriv.h"
+#include "SkJpegUtility.h"
+
+/*
+ * Initialize the source manager
+ */
+static void sk_init_source(j_decompress_ptr jpegInfo) {
+    skjpeg_source_mgr* src = (skjpeg_source_mgr*) jpegInfo->src;
+    src->next_input_byte = (const JOCTET*) src->fBuffer;
+    src->bytes_in_buffer = 0;
+#ifdef SK_BUILD_FOR_ANDROID
+    src->current_offset = 0;
+#endif
+    if (!src->fStream->rewind()) {

[scroggo, 2015/04/10 17:19:07]

We should not need to rewind here?

[msarett, 2015/04/13 20:54:05]

Yes agreed, this is not necessary here.  This was adapted from SkImageDecoder. 
I'm not really sure why it was necessary there either.

+        SkCodecPrintf("Failure to rewind.\n");
+        jpegInfo->err->error_exit((j_common_ptr) jpegInfo);
+    }
+}
+
+/*
+ * Seek to a specific offset in the stream
+ */
+#ifdef SK_BUILD_FOR_ANDROID
+static boolean sk_seek_input_data(j_decompress_ptr jpegInfo, long byteOffset) {

[scroggo, 2015/04/10 17:19:07]

This function (and the rest of the SK_BUILD_FOR_ANDROID code in this file is for
tile based decoding, which we are not intending to support. You can leave it
out.

[msarett, 2015/04/13 20:54:05]

Done.

+    skjpeg_source_mgr* src = (skjpeg_source_mgr*) jpegInfo->src;
+    size_t offset = (size_t) byteOffset;
+
+    if (offset > src->current_offset) {
+        size_t bytesToSkip = offset - src->current_offset;
+        if (bytesToSkip != src->fStream->skip(bytesToSkip)) {
+            SkCodecPrintf("Failure to skip.\n");
+            jpegInfo->err->error_exit((j_common_ptr) jpegInfo);
+            return false;
+        }
+    } else {
+        if (!src->fStream->rewind()) {
+            SkCodecPrintf("Failure to rewind.\n");
+            jpegInfo->err->error_exit((j_common_ptr) jpegInfo);
+            return false;
+        }
+        if (offset != src->fStream->skip(offset)) {
+            SkCodecPrintf("Failure to skip.\n");
+            jpegInfo->err->error_exit((j_common_ptr) jpegInfo);
+            return false;
+        }
+    }
+
+    src->current_offset = offset;
+    src->next_input_byte = (const JOCTET*) src->fBuffer;
+    src->bytes_in_buffer = 0;
+    return true;
+}
+#endif
+
+/*
+ * Fill the input buffer from the stream
+ */
+static boolean sk_fill_input_buffer(j_decompress_ptr jpegInfo) {
+    skjpeg_source_mgr* src = (skjpeg_source_mgr*) jpegInfo->src;
+    size_t bytes = src->fStream->read(src->fBuffer, skjpeg_source_mgr::kBufferSize);
+    
+    // libjpeg is still happy with a less than full read, as long as the result is non-zero
+    if (bytes == 0) {
+        return false;
+    }
+
+#ifdef SK_BUILD_FOR_ANDROID
+    src->current_offset += bytes;
+#endif
+    src->next_input_byte = (const JOCTET*) src->fBuffer;
+    src->bytes_in_buffer = bytes;
+    return true;
+}
+
+/*
+ * Skip a certain number of bytes in the stream
+ */
+static void sk_skip_input_data(j_decompress_ptr jpegInfo, long numBytes) {
+    skjpeg_source_mgr* src = (skjpeg_source_mgr*) jpegInfo->src;
+    size_t bytes = (size_t) numBytes;
+
+    if (bytes > src->bytes_in_buffer) {
+        size_t bytesToSkip = bytes - src->bytes_in_buffer;
+        if (bytesToSkip != src->fStream->skip(bytesToSkip)) {
+            SkCodecPrintf("Failure to skip.\n");
+            jpegInfo->err->error_exit((j_common_ptr)jpegInfo);
+            return;
+        }
+#ifdef SK_BUILD_FOR_ANDROID
+        src->current_offset += bytesToSkip;
+#endif
+        src->next_input_byte = (const JOCTET*) src->fBuffer;
+        src->bytes_in_buffer = 0;
+    } else {
+        src->next_input_byte += numBytes;
+        src->bytes_in_buffer -= numBytes;
+    }
+}
+
+/*
+ * We do not need to do anything to terminate our stream
+ */
+static void sk_term_source(j_decompress_ptr jpegInfo)
+{}
+
+/*
+ * Constructor for the source manager that we provide to libjpeg
+ * We provide skia implementations of all of the stream processing functions required by libjpeg
+ */
+skjpeg_source_mgr::skjpeg_source_mgr(SkStream* stream)
+    : fStream(stream)
+{
+    init_source = sk_init_source;
+    fill_input_buffer = sk_fill_input_buffer;
+    skip_input_data = sk_skip_input_data;
+    resync_to_restart = jpeg_resync_to_restart;
+    term_source = sk_term_source;
+#ifdef SK_BUILD_FOR_ANDROID
+    seek_input_data = sk_seek_input_data;
+#endif
+}
+
+/*
+ * Exit on an error
+ */
+void skjpeg_err_exit(j_common_ptr jpegInfo) {
+    // Simply return to Skia client code
+    // JpegAutoClean should take care of freeing memory
+    skjpeg_error_mgr* error = (skjpeg_error_mgr*) jpegInfo->err;
+    (*error->output_message) (jpegInfo);
+    longjmp(error->fJmpBuf, 1);
+}