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LodePNG is a PNG image decoder and encoder, all in one, no dependency or linkage to zlib or libpng required. It's made for C (ISO C90), and has a C++ wrapper with a more convenient interface on top. See lodepng.h for documentation.
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There is also picoPNG, which is only the decoder part of LodePNG, wrapped in one single C++ function of around 500 lines. This is less well maintained than LodePNG, has less features, and may be less efficient.
The function, decodePNG, converts any PNG file data, with any colortype or interlace mode, into a 32-bit image in an std::vector at the output.
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A: LodePNG uses a pixel order where it goes in rows from top to bottom. In OpenGL, how would you define upside down? There are many things which affect the orientation with which something is drawn in OpenGL: camera orientation, texture coordinates, the orientation of the object, ... If you don't want to solve the problem by changing OpenGL coordinates, e.g. because your game engine uses a bottom to top representation for all textures, you can still go through the raw pixel buffer of LodePNG with a for loop and swap the rows to become upside down. Remember that for 32-bit RGBA, each row is (width * 4 bytes) long, for 24-bit RGB it's (width * 3 bytes) long.
Q: The image is wrong when using LodePNG with BITMAPs in Visual Studio or win32, or with BMP images.
A: LodePNG uses raw buffers with RGBA or RGB pixels in the common order RGBARGBARGBA... or RGBRGBRGBRGB..., from top to bottom, without any special byte boundaries. BMP images and bitmaps in win32 use a different format. They do three things differently:
Q: What's the difference between zlib, deflate and gzip? And between CRC32 and ADLER32?
A: That can be confusing. In short:
A: Try LodePNG instead. It supports more than picoPNG, and is better maintained. The code of picoPNG may be small, but its compiled executable may not be. If you want to compile to a really small executable, then LodePNG can probably do this better because it supports the C language instead of only C++, and has the ability to turn off pieces of code you don't need by changing some #defines in the header.
Q: Error 29 when loading PNG when using XCode.
A: XCode may modify PNG images to a proprietary file format not compatible with the real PNG standard. Disable a setting "Compress PNG Files" under "Packaging" to get valid PNGs.
Q: Why did the interface of LodePNG change? Why not keep it as is, fixing compile errors is annoying!
A: Sorry about that. Sometimes when a feature is added the interface grows into something inconsistent, and then I try to redesign it to get a new, better, one. And sometimes when a new feature is added the cleanest way to do it requires an interface change. In the last change, the following improvements were made that changed it:
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