in src/codec/SkBmpCodec.cpp [148:599]
SkCodec::Result SkBmpCodec::ReadHeader(SkStream* stream, bool inIco,
std::unique_ptr<SkCodec>* codecOut) {
// The total bytes in the bmp file
// We only need to use this value for RLE decoding, so we will only
// check that it is valid in the RLE case.
uint32_t totalBytes;
// The offset from the start of the file where the pixel data begins
uint32_t offset;
// The size of the second (info) header in bytes
uint32_t infoBytes;
// Bmps embedded in Icos skip the first Bmp header
if (!inIco) {
// Read the first header and the size of the second header
uint8_t hBuffer[kBmpHeaderBytesPlusFour];
if (stream->read(hBuffer, kBmpHeaderBytesPlusFour) !=
kBmpHeaderBytesPlusFour) {
SkCodecPrintf("Error: unable to read first bitmap header.\n");
return kIncompleteInput;
}
totalBytes = SkCodecPriv::UnsafeGetInt(hBuffer, 2);
offset = SkCodecPriv::UnsafeGetInt(hBuffer, 10);
if (offset < kBmpHeaderBytes + kBmpOS2V1Bytes) {
SkCodecPrintf("Error: invalid starting location for pixel data\n");
return kInvalidInput;
}
// The size of the second (info) header in bytes
// The size is the first field of the second header, so we have already
// read the first four infoBytes.
infoBytes = SkCodecPriv::UnsafeGetInt(hBuffer, 14);
if (infoBytes < kBmpOS2V1Bytes) {
SkCodecPrintf("Error: invalid second header size.\n");
return kInvalidInput;
}
} else {
// This value is only used by RLE compression. Bmp in Ico files do not
// use RLE. If the compression field is incorrectly signaled as RLE,
// we will catch this and signal an error below.
totalBytes = 0;
// Bmps in Ico cannot specify an offset. We will always assume that
// pixel data begins immediately after the color table. This value
// will be corrected below.
offset = 0;
// Read the size of the second header
uint8_t hBuffer[4];
if (stream->read(hBuffer, 4) != 4) {
SkCodecPrintf("Error: unable to read size of second bitmap header.\n");
return kIncompleteInput;
}
infoBytes = SkCodecPriv::UnsafeGetInt(hBuffer, 0);
if (infoBytes < kBmpOS2V1Bytes) {
SkCodecPrintf("Error: invalid second header size.\n");
return kInvalidInput;
}
}
// Determine image information depending on second header format
const BmpHeaderType headerType = get_header_type(infoBytes);
if (kUnknown_BmpHeaderType == headerType) {
return kInvalidInput;
}
// We already read the first four bytes of the info header to get the size
const uint32_t infoBytesRemaining = infoBytes - 4;
// Read the second header
std::unique_ptr<uint8_t[]> iBuffer(new uint8_t[infoBytesRemaining]);
if (stream->read(iBuffer.get(), infoBytesRemaining) != infoBytesRemaining) {
SkCodecPrintf("Error: unable to read second bitmap header.\n");
return kIncompleteInput;
}
// The number of bits used per pixel in the pixel data
uint16_t bitsPerPixel;
// The compression method for the pixel data
uint32_t compression = kNone_BmpCompressionMethod;
// Number of colors in the color table, defaults to 0 or max (see below)
uint32_t numColors = 0;
// Bytes per color in the color table, early versions use 3, most use 4
uint32_t bytesPerColor;
// The image width and height
int width, height;
switch (headerType) {
case kInfoV1_BmpHeaderType:
case kInfoV2_BmpHeaderType:
case kInfoV3_BmpHeaderType:
case kInfoV4_BmpHeaderType:
case kInfoV5_BmpHeaderType:
case kOS2VX_BmpHeaderType:
// We check the size of the header before entering the if statement.
// We should not reach this point unless the size is large enough for
// these required fields.
SkASSERT(infoBytesRemaining >= 12);
width = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 0);
height = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 4);
bitsPerPixel = SkCodecPriv::UnsafeGetShort(iBuffer.get(), 10);
// Some versions do not have these fields, so we check before
// overwriting the default value.
if (infoBytesRemaining >= 16) {
compression = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 12);
if (infoBytesRemaining >= 32) {
numColors = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 28);
}
}
// All of the headers that reach this point, store color table entries
// using 4 bytes per pixel.
bytesPerColor = 4;
break;
case kOS2V1_BmpHeaderType:
// The OS2V1 is treated separately because it has a unique format
width = (int)SkCodecPriv::UnsafeGetShort(iBuffer.get(), 0);
height = (int)SkCodecPriv::UnsafeGetShort(iBuffer.get(), 2);
bitsPerPixel = SkCodecPriv::UnsafeGetShort(iBuffer.get(), 6);
bytesPerColor = 3;
break;
case kUnknown_BmpHeaderType:
// We'll exit above in this case.
SkASSERT(false);
return kInvalidInput;
}
// Check for valid dimensions from header
SkCodec::SkScanlineOrder rowOrder = SkCodec::kBottomUp_SkScanlineOrder;
if (height < 0) {
// We can't negate INT32_MIN.
if (height == INT32_MIN) {
return kInvalidInput;
}
height = -height;
rowOrder = SkCodec::kTopDown_SkScanlineOrder;
}
// The height field for bmp in ico is double the actual height because they
// contain an XOR mask followed by an AND mask
if (inIco) {
height /= 2;
}
// Arbitrary maximum. Matches Chromium.
constexpr int kMaxDim = 1 << 16;
if (width <= 0 || height <= 0 || width >= kMaxDim || height >= kMaxDim) {
SkCodecPrintf("Error: invalid bitmap dimensions.\n");
return kInvalidInput;
}
// Create mask struct
SkMasks::InputMasks inputMasks;
memset(&inputMasks, 0, sizeof(SkMasks::InputMasks));
// Determine the input compression format and set bit masks if necessary
uint32_t maskBytes = 0;
BmpInputFormat inputFormat = kUnknown_BmpInputFormat;
switch (compression) {
case kNone_BmpCompressionMethod:
inputFormat = kStandard_BmpInputFormat;
// In addition to more standard pixel compression formats, bmp supports
// the use of bit masks to determine pixel components. The standard
// format for representing 16-bit colors is 555 (XRRRRRGGGGGBBBBB),
// which does not map well to any Skia color formats. For this reason,
// we will always enable mask mode with 16 bits per pixel.
if (16 == bitsPerPixel) {
inputMasks.red = 0x7C00;
inputMasks.green = 0x03E0;
inputMasks.blue = 0x001F;
inputFormat = kBitMask_BmpInputFormat;
}
break;
case k8BitRLE_BmpCompressionMethod:
if (bitsPerPixel != 8) {
SkCodecPrintf("Warning: correcting invalid bitmap format.\n");
bitsPerPixel = 8;
}
inputFormat = kRLE_BmpInputFormat;
break;
case k4BitRLE_BmpCompressionMethod:
if (bitsPerPixel != 4) {
SkCodecPrintf("Warning: correcting invalid bitmap format.\n");
bitsPerPixel = 4;
}
inputFormat = kRLE_BmpInputFormat;
break;
case kAlphaBitMasks_BmpCompressionMethod:
case kBitMasks_BmpCompressionMethod:
// Load the masks
inputFormat = kBitMask_BmpInputFormat;
switch (headerType) {
case kInfoV1_BmpHeaderType: {
// The V1 header stores the bit masks after the header
uint8_t buffer[kBmpMaskBytes];
if (stream->read(buffer, kBmpMaskBytes) != kBmpMaskBytes) {
SkCodecPrintf("Error: unable to read bit inputMasks.\n");
return kIncompleteInput;
}
maskBytes = kBmpMaskBytes;
inputMasks.red = SkCodecPriv::UnsafeGetInt(buffer, 0);
inputMasks.green = SkCodecPriv::UnsafeGetInt(buffer, 4);
inputMasks.blue = SkCodecPriv::UnsafeGetInt(buffer, 8);
break;
}
case kInfoV2_BmpHeaderType:
case kInfoV3_BmpHeaderType:
case kInfoV4_BmpHeaderType:
case kInfoV5_BmpHeaderType:
// Header types are matched based on size. If the header
// is V2+, we are guaranteed to be able to read at least
// this size.
SkASSERT(infoBytesRemaining >= 48);
inputMasks.red = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 36);
inputMasks.green = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 40);
inputMasks.blue = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 44);
if (kInfoV2_BmpHeaderType == headerType ||
(kInfoV3_BmpHeaderType == headerType && !inIco)) {
break;
}
// V3+ bmp files introduce an alpha mask and allow the creator of the image
// to use the alpha channels. However, many of these images leave the
// alpha channel blank and expect to be rendered as opaque. This is the
// case for almost all V3 images, so we ignore the alpha mask. For V4+
// images in kMask mode, we will use the alpha mask. Additionally, V3
// bmp-in-ico expect us to use the alpha mask.
//
// skbug.com/4116: We should perhaps also apply the alpha mask in kStandard
// mode. We just haven't seen any images that expect this
// behavior.
//
// Header types are matched based on size. If the header is
// V3+, we are guaranteed to be able to read at least this size.
SkASSERT(infoBytesRemaining >= 52);
inputMasks.alpha = SkCodecPriv::UnsafeGetInt(iBuffer.get(), 48);
break;
case kOS2VX_BmpHeaderType:
// TODO: Decide if we intend to support this.
// It is unsupported in the previous version and
// in chromium. I have not come across a test case
// that uses this format.
SkCodecPrintf("Error: huffman format unsupported.\n");
return kUnimplemented;
default:
SkCodecPrintf("Error: invalid bmp bit masks header.\n");
return kInvalidInput;
}
break;
case kJpeg_BmpCompressionMethod:
if (24 == bitsPerPixel) {
inputFormat = kRLE_BmpInputFormat;
break;
}
[[fallthrough]];
case kPng_BmpCompressionMethod:
// TODO: Decide if we intend to support this.
// It is unsupported in the previous version and
// in chromium. I think it is used mostly for printers.
SkCodecPrintf("Error: compression format not supported.\n");
return kUnimplemented;
case kCMYK_BmpCompressionMethod:
case kCMYK8BitRLE_BmpCompressionMethod:
case kCMYK4BitRLE_BmpCompressionMethod:
// TODO: Same as above.
SkCodecPrintf("Error: CMYK not supported for bitmap decoding.\n");
return kUnimplemented;
default:
SkCodecPrintf("Error: invalid format for bitmap decoding.\n");
return kInvalidInput;
}
iBuffer.reset();
// Calculate the number of bytes read so far
const uint32_t bytesRead = kBmpHeaderBytes + infoBytes + maskBytes;
if (!inIco && offset < bytesRead) {
// TODO (msarett): Do we really want to fail if the offset in the header is invalid?
// Seems like we can just assume that the offset is zero and try to decode?
// Maybe we don't want to try to decode corrupt images?
SkCodecPrintf("Error: pixel data offset less than header size.\n");
return kInvalidInput;
}
switch (inputFormat) {
case kStandard_BmpInputFormat: {
// BMPs are generally opaque, however BMPs-in-ICOs may contain
// a transparency mask after the image. Therefore, we mark the
// alpha as kBinary if the BMP is contained in an ICO.
// We use |isOpaque| to indicate if the BMP itself is opaque.
SkEncodedInfo::Alpha alpha = inIco ? SkEncodedInfo::kBinary_Alpha :
SkEncodedInfo::kOpaque_Alpha;
bool isOpaque = true;
SkEncodedInfo::Color color;
uint8_t bitsPerComponent;
switch (bitsPerPixel) {
// Palette formats
case 1:
case 2:
case 4:
case 8:
// In the case of ICO, kBGRA is actually the closest match,
// since we will need to apply a transparency mask.
if (inIco) {
color = SkEncodedInfo::kBGRA_Color;
bitsPerComponent = 8;
} else {
color = SkEncodedInfo::kPalette_Color;
bitsPerComponent = (uint8_t) bitsPerPixel;
}
break;
case 24:
// In the case of ICO, kBGRA is actually the closest match,
// since we will need to apply a transparency mask.
color = inIco ? SkEncodedInfo::kBGRA_Color : SkEncodedInfo::kBGR_Color;
bitsPerComponent = 8;
break;
case 32:
// 32-bit BMP-in-ICOs actually use the alpha channel in place of a
// transparency mask.
if (inIco) {
isOpaque = false;
alpha = SkEncodedInfo::kUnpremul_Alpha;
color = SkEncodedInfo::kBGRA_Color;
} else {
color = SkEncodedInfo::kBGRX_Color;
}
bitsPerComponent = 8;
break;
default:
SkCodecPrintf("Error: invalid input value for bits per pixel.\n");
return kInvalidInput;
}
if (codecOut) {
// We require streams to have a memory base for Bmp-in-Ico decodes.
SkASSERT(!inIco || nullptr != stream->getMemoryBase());
// Set the image info and create a codec.
auto info = SkEncodedInfo::Make(width, height, color, alpha, bitsPerComponent);
*codecOut = std::make_unique<SkBmpStandardCodec>(std::move(info),
std::unique_ptr<SkStream>(stream),
bitsPerPixel, numColors, bytesPerColor,
offset - bytesRead, rowOrder, isOpaque,
inIco);
return static_cast<SkBmpStandardCodec*>(codecOut->get())->didCreateSrcBuffer()
? kSuccess : kInvalidInput;
}
return kSuccess;
}
case kBitMask_BmpInputFormat: {
// Bmp-in-Ico must be standard mode
if (inIco) {
SkCodecPrintf("Error: Icos may not use bit mask format.\n");
return kInvalidInput;
}
switch (bitsPerPixel) {
case 16:
case 24:
case 32:
break;
default:
SkCodecPrintf("Error: invalid input value for bits per pixel.\n");
return kInvalidInput;
}
// Skip to the start of the pixel array.
// We can do this here because there is no color table to read
// in bit mask mode.
if (stream->skip(offset - bytesRead) != offset - bytesRead) {
SkCodecPrintf("Error: unable to skip to image data.\n");
return kIncompleteInput;
}
if (codecOut) {
// Check that input bit masks are valid and create the masks object
SkASSERT(bitsPerPixel % 8 == 0);
std::unique_ptr<SkMasks> masks(SkMasks::CreateMasks(inputMasks, bitsPerPixel/8));
if (nullptr == masks) {
SkCodecPrintf("Error: invalid input masks.\n");
return kInvalidInput;
}
// Masked bmps are not a great fit for SkEncodedInfo, since they have
// arbitrary component orderings and bits per component. Here we choose
// somewhat reasonable values - it's ok that we don't match exactly
// because SkBmpMaskCodec has its own mask swizzler anyway.
SkEncodedInfo::Color color;
SkEncodedInfo::Alpha alpha;
if (masks->getAlphaMask()) {
color = SkEncodedInfo::kBGRA_Color;
alpha = SkEncodedInfo::kUnpremul_Alpha;
} else {
color = SkEncodedInfo::kBGR_Color;
alpha = SkEncodedInfo::kOpaque_Alpha;
}
auto info = SkEncodedInfo::Make(width, height, color, alpha, 8);
*codecOut = std::make_unique<SkBmpMaskCodec>(std::move(info),
std::unique_ptr<SkStream>(stream), bitsPerPixel,
masks.release(), rowOrder);
return static_cast<SkBmpMaskCodec*>(codecOut->get())->didCreateSrcBuffer()
? kSuccess : kInvalidInput;
}
return kSuccess;
}
case kRLE_BmpInputFormat: {
// We should not reach this point without a valid value of bitsPerPixel.
SkASSERT(4 == bitsPerPixel || 8 == bitsPerPixel || 24 == bitsPerPixel);
// Check for a valid number of total bytes when in RLE mode
if (totalBytes <= offset) {
SkCodecPrintf("Error: RLE requires valid input size.\n");
return kInvalidInput;
}
// Bmp-in-Ico must be standard mode
// When inIco is true, this line cannot be reached, since we
// require that RLE Bmps have a valid number of totalBytes, and
// Icos skip the header that contains totalBytes.
SkASSERT(!inIco);
if (codecOut) {
// RLE inputs may skip pixels, leaving them as transparent. This
// is uncommon, but we cannot be certain that an RLE bmp will be
// opaque or that we will be able to represent it with a palette.
// For that reason, we always indicate that we are kBGRA.
auto info = SkEncodedInfo::Make(width, height, SkEncodedInfo::kBGRA_Color,
SkEncodedInfo::kBinary_Alpha, 8);
*codecOut = std::make_unique<SkBmpRLECodec>(std::move(info),
std::unique_ptr<SkStream>(stream), bitsPerPixel,
numColors, bytesPerColor, offset - bytesRead,
rowOrder);
}
return kSuccess;
}
default:
SkASSERT(false);
return kInvalidInput;
}
}