How to "Padding" Image in C++ - c++

Question

I am running for displaying RGB image from raw in C++ without any library. When I input the square image (e.g: 512x512), my program can display the image perfectly, but it does not in not_square size image (e.g: 350x225). I understand that I need padding for this case, then I tried to find the same case but it didn't make sense for me how people can pad their image.
If anyone can show me how to pad, I would be thanks for this. And below is what I have done for RGB from Raw.
void CImage_MyClass::Class_MakeRGB(void)
{
m_BMPheader.biHeight = m_uiHeight;
m_BMPheader.biWidth = m_uiWidth;
m_pcBMP = new UCHAR[m_uiHeight * m_uiWidth * 3];
//RGB Image
{
int ind = 0;
for (UINT y = 0; y < m_uiHeight; y++)
{
for (UINT x = 0; x < m_uiHeight*3; x+=3)
{
m_pcBMP[ind++] = m_pcIBuff[m_uiHeight - y -1][x+2];
m_pcBMP[ind++] = m_pcIBuff[m_uiHeight - y -1][x+1];
m_pcBMP[ind++] = m_pcIBuff[m_uiHeight - y -1][x];
}
}
}
}

Answer 1

You need to pad the number of bytes in each line out to a multiple of 4.
void CImage_MyClass::Class_MakeRGB(void)
{
m_BMPheader.biHeight = m_uiHeight;
m_BMPheader.biWidth = m_uiWidth;
//Pad buffer width to next highest multiple of 4
const int bmStride = m_uiWidth * 3 + 3 & ~3;
m_pcBMP = new UCHAR[m_uiHeight * bmStride];
//Clear buffer so the padding bytes are 0
memset(m_pcBMP, 0, m_uiHeight * bmStride);
//RGB Image
{
for(UINT y = 0; y < m_uiHeight; y++)
{
for(UINT x = 0; x < m_uiWidth * 3; x += 3)
{
const int bmpPos = y * bmWidth + x;
m_pcBMP[bmpPos + 0] = m_pcIBuff[m_uiHeight - y - 1][x + 2];
m_pcBMP[bmpPos + 1] = m_pcIBuff[m_uiHeight - y - 1][x + 1];
m_pcBMP[bmpPos + 2] = m_pcIBuff[m_uiHeight - y - 1][x];
}
}
}
}
I also changed the inner for loop to use m_uiWidth instead of m_uiHeight.

Answer 2

#Retired Ninja, Thanks anyway for your answer... you showed me a simple way for this...
But by the way, I have fixed mine as well with different way.. here is it:
void CImage_MyClass::Class_MakeRGB(void)
{
m_BMPheader.biHeight = m_uiHeight;
m_BMPheader.biWidth = m_uiWidth;
int padding = 0;
int scanline = m_uiWidth * 3;
while ( ( scanline + padding ) % 4 != 0 )
{
padding++;
}
int psw = scanline + padding;
m_pcBMP = new UCHAR[m_uiHeight * m_uiWidth * 3 + m_uiHeight * padding];
//RGB Image
int ind = 0;
for (UINT y = 0; y < m_uiHeight; y++)
{
for (UINT x = 0; x < m_uiHeight*3; x+=3)
{
m_pcBMP[ind++] = m_pcIBuff[m_uiHeight - y -1][x+2];
m_pcBMP[ind++] = m_pcIBuff[m_uiHeight - y -1][x+1];
m_pcBMP[ind++] = m_pcIBuff[m_uiHeight - y -1][x];
}
for(int i = 0; i < padding; i++)
ind++;
}
}