GDI+ gif speed problem

I am using开发者_开发知识库 C++ GDI+ to open a gif

however I find the frame interval is really strange. It is different from played it by window's pic viewer.

The code I written is as follow.

pMultiPageImg = new Bitmap(XXXXX);
int size = m_pMultiPageImg->GetPropertyItemSize(PropertyTagFrameDelay);
m_pTimeDelays = (PropertyItem*) malloc (size);
m_pMultiPageImg->GetPropertyItem(PropertyTagFrameDelay, size, m_pTimeDelays);
int frameSize =  m_pMultiPageImg->GetFrameDimensionsCount();();

// the interal of frame FrameNumber:
long lPause = ((long*)m_pTimeDelays->value)[FrameNumber] * 10;

however I found some frame the lPause <= 0. What does this mean?

And are code I listed right for get the interval?

Many thanks!

The frame duration field in the gif header is only two bytes long (interpreted as 100ths of a second - allowing values from 0 to 32.768 seconds).

You seem to be interpreting it as long, which is probably 4 bytes on your platform so you will be reading another field along with the duration. It is hard to tell from the code you provide, but I think this is the problem.

Frame delays should not be negative numbers. I think the error comes in during the array type conversion or "FrameNumber" goes out of bounds.

1. GetPropertyItemSize(PropertyTagFrameDelay) returns a native byte array. It'll be safer to convert it to an Int32 array instead of a "long" array. "long" is always 4 bytes long under 32-bit systems, but could be 8 bytes under some 64-bit systems.

2. m_pMultiPageImg->GetFrameDimensionsCount() returns the number of frame dimensions in the image, not the number of frames. The dimension of the first frame (master image) is usually used in order to get the frame count.

In your case, the code looks like

int count = m_pMultiPageImg->GetFrameDimensionsCount();
GUID* dimensionIDs = new GUID[count];
m_pMultiPageImg->GetFrameDimensionsList(dimensionIDs, count);
int frameCount = m_pMultiPageImg->GetFrameCount(&m_pDimensionIDs[0]);

Hope this helps.