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[mechacrash]

Hey, i am working on a bitmap loader and the last thing i need to do now is RLE compression for 8 and 4 bit bitmaps. I looked at this website: http://gpwiki.org/index.php/LoadBMPCpp and it had code for RLE8 compression. However I do not think this is working as i have copied this almost exactly. When I try to display this in OpenGL I use the type GL_RGB I tried using GL_COLOR_INDEX and nothing appeared, but with GL_RGB the image appears but it is distorted in its colors, it is wrapped around the bottom of the texture and the top is black but the image is half decrypted. I was wondering if anyone knows a website with more on RLE encryption and maybe something decrypting images in C++/OpenGL.

Thanks

[BorisTheBrave]

Odd graphical glitches usually come from miscalculating the stride of your bitmap, which is not always width * size of one pixel.

But really, why are you doing this, when you could just use pngs? I am sure they compress better than RLE (consider that you can store each pixel as a delta from the previous), and you'd already have premade libraries.

[mechacrash]

I'm making a loader for lots of different file types. I don't understand why that example isn't working for me.

[Mikademus]

i have copied this almost exactly

I'd start there.

[mechacrash]

Well all I have done is change the variable names.

[David Pittman]

For starters, don't trust this code. It looks sketchy to me. Put some breakpoints in BMPImg::LoadBmpRLE8() and make sure it isn't hitting any weird cases.

This looks especially suspect:

Code:

case 2:  // Reposition, Never used
  break;

I'd double-check that that case isn't needed in your BMPs--reading about the file format (e.g., here) doesn't suggest that it is actually never used; it may simply be a case the author chose not to handle because his image tools did not export BMPs with that indicator.

Also:

Code:

if(iIndex>iDataSize) // Stop if image size exceeded.
  iDcode=0;

That seems like it should be reporting a warning or assertion failed if not an explicit hard failure case; if image size is exceeded, the program clearly failed in either calculating the image size or reading the data.

Honestly, if you're trying to write your own image loader, you should start by reading the file format spec, and then actually write your own code instead of copying something else. Or if that sounds like a lot of reinventing the wheel, don't write your own image loader. Find a library that does what you need and has been proven in other people's games, and use that instead.

[mechacrash]

I looked around on google and i found out about GL_IMAGE_INDEX, i think the RLE8 loader on this website loads the image into and image index format as opposed to RGB so i'm looking for a way to convert from image index to rgb using GL_PIXEL_MAP_I_TO_R G and B. But when I have a chance I will make a new bitmap with RLE8 compression and test it using the spec to see if this function works