Detecting .png alpha channel in Windows/D3D

I'm loading a texture from .png using D3DXCreateTextureFromFile(). How can my program kn开发者_StackOverflow社区ow if the image file contains an alpha channel?

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This isn't too hard to do by simply examining the file.

A PNG file consists of:

• A file header
• One or more 'chunks'

The file header is always 8 bytes and should be skipped over.

Each chunk begins with 4 bytes indicating its length, and 4 bytes indicating its type. The first chunk should always be 13 bytes and have the type IHDR. This contains the information about the image.

The tenth byte in the header contains the exact information you're looking for. It will be equal to 6 if the PNG file is RGBA.

More information can be found here.

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Call IDirect3DTexture9::GetSurfaceLevel and then call IDirect3DSurface9::GetDesc. The D3DSURFACE_DESC.Format member will tell you.