pangolin: add package

[star-hengxing]

No description provided.

[gemini-code-assist]

Summary of Changes

Hello @star-hengxing, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request integrates the Pangolin library into the package management system by adding its definition. This enables developers to easily incorporate Pangolin, a library for OpenGL display and video input, into their projects, streamlining the setup and build process across various platforms.

Highlights

• New Package Definition: Introduces the pangolin package, a lightweight library for OpenGL display and video input, complete with its homepage, description, license (MIT), and source URLs.
• Platform-Specific System Links: Configures system library links (pthread, rt for Linux/BSD; shlwapi, gdi32, user32, shell32 for Windows/MinGW; Cocoa framework for macOS) based on the target platform.
• Dependencies Management: Declares cmake and eigen as core dependencies, and conditionally adds glew (for non-WASM/Linux) or libepoxy (for Linux) to provide necessary OpenGL support.
• Conditional Defines: Sets platform-specific preprocessor defines (_WIN_, _LINUX_, _OSX_, _EMSCRIPTEN_) and OpenGL-related defines (HAVE_GLES, HAVE_GLES_2, HAVE_GLEW, HAVE_EPOXY) during the package loading phase.
• CMake-based Installation: Implements an on_install function that leverages CMake to build the package, allowing for flexible configuration of shared libraries, debug/release builds, optional tools, and handling of the GLEW_STATIC define for static glew linking.
• Basic Functionality Test: Includes a C++ snippet test to verify the fundamental functionality of Pangolin, specifically demonstrating the creation of an OpenGL window, ensuring the package can be used correctly post-installation.

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[gemini-code-assist]

Code Review

This pull request adds a new package for the pangolin library. The implementation is mostly correct, but I've identified a few areas for improvement. My feedback includes suggestions to align with repository conventions for versioning, simplify conditional logic for dependencies to improve readability, and use a more idiomatic approach for setting compiler definitions during the build process. These changes will enhance the maintainability and robustness of the package definition.