OpenIL (DevIL): Using ilLoadL from Delphi

Question

Hi, I'm trying to manipulate an image that I receive to a function as TStream. I want to load it from memory and avoid writing to files.

input variable declared as:

inImage: TStream;

"lump" variable declared as:

imgLump: Array of TILubyte;

in the function I do as follows:

// setting input image into a "lump" 
SetLength(imgLump, inImage.Size); 
// rewind stream to beginning 
inImage.Seek(0, soBeginning); 
// read stream and write into array 
inImage.Read(imgLump[0], inImage.Size); 
loaded := ilLoadL(IL_JPG, imgLump, Length(imgLump));

---

at this stage, loaded gets the value 0 (IL_FALSE) and the call to ilGetError() returns 1298 (IL_FILE_READ_ERROR).

why?! what did I miss?

Thanks, Ilan

Answer 1

First try this:

loaded := ilLoadL(IL_JPG, @imgLump[0], Length(imgLump));

If that doesn't work, try this:

Step 1: Write the stream into a file and try to open it using your favourite image viewer.

It it doesn't work, the stream itself is corrupted.

Step 2: Write the array into a file and check it.

It it doesn't work, the stream-to-array is wrong.

Step 3: If all files are valid, then the problem must be at the call to ilLoadL. Double-check the documentation and/or ask the original developers.

Answer 2

I wouldn't seek in the stream. Most APIs are written to assume that when they've been given a stream, the correct place to read from is the current position. They're supposed to read as much data as they want, and then leave the stream at that position, ready for the next function to continue reading what it needs from the stream. You mustn't assume that the entire stream is yours. The caller might have other stuff beforehand. Or the stream might not support seeking backward, or seeking at all.

Are you sure the stream contains JPEG data? What do the first few bytes look like? Have you tried opening the image with TJpegImage instead?

Is a TILubyte the same as a normal Byte? Is what DevIL calls a "lump" the same as what everyone else would call an ordinary array or memory buffer?