Hi!
I'm not very familiar to C, but I do know a little.
No I'm trying to read someone elses program, and this line (and
simular, less complex lines) realy confuses me. Can someone explain?
I'm not new to the concept of pointers, so I think that I have a fair
chance. :-)
What is this line doing?!?:
srcptr=(MY_PIXE L*)(source->imageData+(t op-j)*source->widthStep)+(le ft-i);
Some header:
#define MY_PIXEL unsigned char
//Only the intresting variabels.
typedef struct _IplImage {
char *imageData; ///< Pointer to aligned image
int widthStep; ///< The size of aligned line in
bytes
...
} IplImage;
int i,j
int left,top;
MY_PIXEL *srcptr;
IplImage *source; // standard Ipl.
best regards,
Andreas Lundgren 1 1790
Andreas wrote: Hi!
I'm not very familiar to C, but I do know a little. No I'm trying to read someone elses program, and this line (and simular, less complex lines) realy confuses me. Can someone explain? I'm not new to the concept of pointers, so I think that I have a fair chance. :-)
What is this line doing?!?: srcptr=(MY_PIXE L*)(source->imageData+(t op-j)*source->widthStep)+(le ft-i);
It's using source->imageData as the start of a 2D array and casting the
entry's address from a pointer to a char to a pointer to an unsigned char,
basically. The arithmetic part is equivalent to:
int x = left - i;
int y = (top - j) * source->widthStep;
source->imageData[x][y];
Or maybe it's [y][x], I always get those confused. In any case, it's
converting a coordinate that's relative to some sub-area of the image
to a coordinate that's relative to the upper-left corner of the entire
image.
Matt Gregory
Some header: #define MY_PIXEL unsigned char //Only the intresting variabels. typedef struct _IplImage { char *imageData; ///< Pointer to aligned image int widthStep; ///< The size of aligned line in bytes ... } IplImage; int i,j int left,top; MY_PIXEL *srcptr; IplImage *source; // standard Ipl.
best regards, Andreas Lundgren This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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