How does the Gallery application work on Android?

I know that Android is an open source system, so all the code should be available for the world to see. I am interested in only one application: the Gallery application.

Where could I find the the source code for the Gallery application, so that I can download and study it?

EDIT:

Just to make it clear, I am not asking about the gallery widget that comes in the SDK. I am asking about the photoviewing application that 开发者_高级运维comes on all Android OS.

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You can find it here, check this link:
https://android.googlesource.com/platform/packages/apps/Gallery/