Ensure the callback run engine core mainLoop,
This commit can solve any weird behaviors, such as:
a. text render maybe missing charactors when bring from back to frontend
b. some renderer objects alpha may present black at sdk callback call
c. some other things
All above behavior is caused gl state not ready when go back to game activity from sdk activity
* PixelFormat use table
* Correct PixelFormat name to match 'GL_LUMINANCE'
* Up
* fix cube update texture enum
* linux build
* Refine ci
* fix linux build
* Remove unused function, match mtl framebuffer pixel format
* readPixels always RGBA format
* fix ci for linux
* fix linux build
* Remove unused functions
* fix travis
* fix android ci
* Update config.json
* linux glad
* Update CCGLViewImpl-desktop.cpp
* fix linux build
* Fix linux build
* Link issue [skip appveyor][skip travis]
* Update CMakeLists.txt
* Refine GL enums use
* Update test case name [skip appveyor][skip travis]
* fix linux link issue
* for mtl
* fix ci
* Tidy pixelformat enums
* fix ci
* fix rgba8 to abgr4 error
* fix ci
* fix ci for GLES
* Fix linux build, require glibc-2.27+
* Use properly dist for travis [skip appveyor]
* fix linux build [skip appveyor]
* Update install-deps-linux.sh
* Remove unused members for pixel block info, update external to v73
* Sync from compile linux warnings
* Remove unused check, and PixelFormat::A8 is ordinary format, not compressed format
* metal doesn't support rgb8 (#3)
* Update CCTexture2D.cpp
* Refine code
* Pixel Format Descriptor Table
* fix ci
* BGR5A1
* Simplfy texture format convert function name
* Update
* rgba4 match mtl render format
* Add note about RGBA4
* Remove unused function
* fix osx
* Already converted at texture2d
* Clearly comment
* fixup