Bitmap/C++

From Rosetta Code
< Bitmap(Redirected from Basic bitmap storage/C++)
Bitmap/C++ is part of Basic bitmap storage. You may find other members of Basic bitmap storage at Category:Basic bitmap storage.
#include <cstddef>
#include <stdexcept>
 
// CBitmap as found below is a class that represents bitmap images
// in main memory, alternatively the images could be stored in
// memory in a graphics system (OpenGL, DirectX, ...), but this
// would not be generic, nor simple.
 
class CBitmap
{
private:
enum { red_index, green_index, blue_index, num_channels };
 
private:
char* m_pImageData;
unsigned int m_width;
unsigned int m_height;
 
public:
// If allocation fails, "new" will throw a std::bad_alloc exception.
// For automatic variables, the result is that all accesses to the
// class' members are skipped, by leaving the scope where the object
// is created, and visible.
// For dynamic variables, created on the heap, this will not result
// in a memory leak, because the memory allocated for the CBitmap
// is freed as a result of the exception in this case. It is the
// responsability of the client not to access the class' members
// after such a failed allocation.
// The result of this is that the m_pImageData member variable
// will never be 0 in a legal access through the class' member
// functions, and thus we can be certain of the invariant (m_pImageData != 0).
CBitmap(unsigned int width, unsigned int height):
m_pImageData(new char[num_channels * width * height]),
m_width(width),
m_height(height)
{
}
 
// The presence of this copy constructor enables pass-by-value,
// which is strongly discouraged, due to large amount of work
// involved in copying. Use pass-by-reference to avoid the copy.
CBitmap(CBitmap const &original):
m_pImageData(new char[num_channels * original.m_width * original.m_height]),
m_width(original.m_width),
m_height(original.m_height)
{
CopyImageDataFrom(original.m_pImageData);
}
 
~CBitmap()
{
delete [] m_pImageData;
}
 
public:
// An assignment operator is defined with copy-semantics. When an
// allocation error occurs, an exception is thrown (which should
// be caught by the client, and the object destructed) and the
// original data is preserved, to satisfy the invariant (m_pImageData != 0).
 
// post-condition: this bitmap becomes a uniform copy of the original.
// exception: failed allocation will cause the image data to be unchanged.
CBitmap& operator=(CBitmap const &original)
{
if ( this == &original )
{
return *this;
}
 
try
{
char *new_image_data = new char[num_channels * original.m_width * original.m_height];
delete [] m_pImageData;
m_pImageData = new_image_data;
m_width = original.m_width;
m_height = original.m_height;
CopyImageDataFrom(original.m_pImageData);
}
catch ( ... )
{
throw std::runtime_error( "assignment failed, original data conserved" );
}
 
return *this;
}
 
 
public:
bool SetPixel(unsigned int x, unsigned int y, char R, char G, char B)
{
if ( ! IsWithinBitmap(x, y) )
{
return false;
}
 
unsigned int pixel_index = ImageCoordinateToPixelIndex(x, y);
SetColorValueAtIndex( pixel_index, R, G, B );
 
return true;
}
 
bool GetPixel(unsigned int x, unsigned int y, char& R, char& G, char& B)
{
if ( ! IsWithinBitmap(x, y) )
{
return false;
}
 
unsigned int pixel_index = ImageCoordinateToPixelIndex(x, y);
GetColorValueAtIndex( pixel_index, R, G, B );
 
return true;
}
 
void Fill(char R, char G, char B)
{
for(unsigned int pixel_index = 0;
pixel_index < m_height * m_width * num_channels;
pixel_index += num_channels)
SetColorValueAtIndex( pixel_index, R, G, B );
}
 
private:
// An alternative to status flags is the use of exceptions.
bool IsWithinBitmap(unsigned int x, unsigned int y)
{
return y < m_height && x < m_width;
}
 
unsigned int ImageCoordinateToPixelIndex(unsigned int x, unsigned int y)
{
return (y * m_width + x) * num_channels;
}
 
void SetColorValueAtIndex(unsigned int pixel_index, char R, char G, char B)
{
m_pImageData[pixel_index + red_index] = R;
m_pImageData[pixel_index + green_index] = G;
m_pImageData[pixel_index + blue_index] = B;
}
 
void GetColorValueAtIndex(unsigned int pixel_index, char R, char G, char B)
{
R = m_pImageData[pixel_index + red_index];
G = m_pImageData[pixel_index + green_index];
B = m_pImageData[pixel_index + blue_index];
}
 
void CopyImageDataFrom(char *source)
{
// An alternative implementation using memcpy would be more efficient
// on almost all platforms.
for (unsigned int i = 0; i < num_channels * m_width * m_height; ++i)
m_pImageData[i] = source[i];
}
 
};