无法创建某些大小的BMP文件

Question

我正在为我的应用程序创建小型BMP文件，其中一些文件(取决于像素数(会导致我的应用崩溃，Windows会发现它们已损坏。工作大小的示例是60 x 60px，但即61 x 61不是(变量m_width和m_height(。

使用的结构(#pragma包应用于BMP相关的结构(：

struct Rgb /// vector's content
{
uint8_t r;
uint8_t g;
uint8_t b;
};
#pragma pack(push, 1)
struct FileHeader
{
int16_t bfType;
int32_t bfSize;
int16_t bfReserved1;
int16_t bfReserved2;
int32_t bfOffBits;
};
struct BitMapInfoHeader
{
int32_t biSize;   
int32_t biWidth;
int32_t biHeight;
int16_t biPlanes; 
int16_t biBitCount;
int32_t biCompression;
int32_t biSizeImage; 
int32_t biXPelsPerMeter;
int32_t biYPelsPerMeter;
int32_t biClrUsed;
int8_t  biClrImportant;
int8_t  biClrRotation;
int16_t biReserved;
};
struct RGBQuad
{
int8_t rgbBlue;
int8_t rgbGreen;
int8_t rgbRed;
int8_t rgbReserved;
};
#pragma pack(pop)

我为整个BMP文件分配内存，为每个文件区域分配指针，填充结构，从其他数组复制像素数据并保存文件。代码：

int m_width = 60, m_height = 60;
uint8_t* data = new uint8_t[ m_width * m_height ];
memset( data, 0, m_width * m_height );
data[ 2 ] = 1;             /// one pixel differs
std::vector< Rgb > RGBVec = { { 223, 223, 123 }, { 230, 0, 12 } };
int numberOfSymbols = RGBVec.size();
FileHeader* fileHeader;
BitMapInfoHeader* infoHeader;
RGBQuad* colorTable;
uint8_t* m_pBMPFile;        /// pointer to bitmap in memory
uint8_t* m_BMPData;         /// begin of pixel data
int m_BMPFileLength = sizeof( FileHeader ) + sizeof( BitMapInfoHeader )
+ numberOfSymbols * sizeof( RGBQuad ) + m_width * m_height;
/// assign pointers to specific parts of bitmap:
m_pBMPFile = new uint8_t[ m_BMPFileLength ];
memset( m_pBMPFile, 0, m_BMPFileLength );
fileHeader = reinterpret_cast< FileHeader* >( m_pBMPFile );
infoHeader = reinterpret_cast< BitMapInfoHeader* >( m_pBMPFile + sizeof( FileHeader ) );
colorTable =
reinterpret_cast< RGBQuad* >( m_pBMPFile + sizeof( FileHeader ) + sizeof( BitMapInfoHeader ) );
m_BMPData = reinterpret_cast< uint8_t* >( m_pBMPFile + sizeof( FileHeader ) + sizeof( BitMapInfoHeader )
+ numberOfSymbols * sizeof( RGBQuad ) );
///////////
/// FileHeader:
fileHeader->bfType = 0x4d42;            /// magic number
fileHeader->bfSize = m_BMPFileLength;
fileHeader->bfOffBits = int( m_BMPData - m_pBMPFile );
/// BitMapInfoHeader:
infoHeader->biSize = 40;
infoHeader->biWidth = m_width;
infoHeader->biHeight = -m_height;       /// multiplied by -1 so pixels are displayed top-down
infoHeader->biPlanes = 1;
infoHeader->biBitCount = 8;
infoHeader->biCompression = 0;
infoHeader->biSizeImage = 0;
infoHeader->biXPelsPerMeter = 2835;
infoHeader->biYPelsPerMeter = 2835;
infoHeader->biClrUsed = numberOfSymbols;
infoHeader->biClrImportant = 0;
infoHeader->biClrRotation = 0;
/// palette:
int i = 0;
for( auto& s : RGBVec )
{
( &colorTable[ i ] )->rgbRed = s.r;
( &colorTable[ i ] )->rgbGreen = s.g;
( &colorTable[ i ] )->rgbBlue = s.b;
++i;
}
/// apply pixel data:
memcpy( m_BMPData, data, m_width * m_height );
/// save:
std::ofstream file2( "out.bmp", std::ios::binary | std::ios::trunc );
file2.write( ( char* )m_pBMPFile, m_BMPFileLength );
file2.close();
delete[] m_pBMPFile;

在VS2015上编译，64位。

Answer 1

主要问题是应该填充m_width，以便字节宽度可以被4整除。对于width_in_bytes，您可以使用下面的公式来保证这一点。在这种情况下，它将宽度从61更改为64。多余的字节可以忽略。

此外，您可以通过避免过度使用指针来简化代码。将标头声明为局部变量就足够了。使用std::vector来分配data，而不是new/delete。并使用单个RGBQ标头来管理数据。示例：

struct RGBQ { uint8_t rgbBlue, rgbGreen, rgbRed, rgbReserved; };
int m_width = 61, m_height = 61;
int bitcount = 8;
int width_in_bytes = ((m_width * bitcount + 31) / 32) * 4;
int imagesize = width_in_bytes * m_height;
std::vector<RGBQ> color_table{ { 223, 223, 123 }, { 230, 0, 12 } };
std::vector<uint8_t> data(imagesize);
data[2] = 1;
FileHeader fileHeader = { 0 };
BitMapInfoHeader infoHeader = { 0 };
fileHeader.bfType = 0x4d42;            
fileHeader.bfSize = sizeof(fileHeader) + sizeof(infoHeader) + color_table.size()
* sizeof(RGBQ) + data.size();
fileHeader.bfOffBits = sizeof(fileHeader) + sizeof(infoHeader);
infoHeader.biSize = 40;
infoHeader.biWidth = m_width;
infoHeader.biHeight = -m_height;       
infoHeader.biPlanes = 1;
infoHeader.biBitCount = bitcount;
infoHeader.biClrUsed = color_table.size();
std::ofstream file2("out.bmp", std::ios::binary | std::ios::trunc);
file2.write((char*)&fileHeader, sizeof(fileHeader));
file2.write((char*)&infoHeader, sizeof(infoHeader));
file2.write((char*)color_table.data(), color_table.size() * sizeof(RGBQ));
file2.write((char*)data.data(), data.size());
file2.close();