This commit updates bgfx's NanoVG codebase to adapt the latest NanoVG commit since I've implemented blending support for the original NanoVG and there is no need of `nvgState()` anymore.
This commit updates nanovg's bgfx backend to adopt premultiplied alpha as the default blending mode just like the original nanovg. Both the fragment shader and the `glnvg__convertPaint()` function are updated to match the original nanovg counterpart.
However, the binary file of the fragment shader is built on Mac so DirectX support is missing.
This commit ports nanovg's helper functions for rendering stuff in framebuffer defined in `nanovg_gl_utils.h`. Also, a new `nvgState()` function is created for bgfx backend so it is possible to blend between framebuffers, which feature is long requested but not yet supported in original nanovg. The `nvgState()` function can be called between `nvgBeginFrame()` and `nvgEndFrame()`.
This commit fixes the bug that the bgfx does not respect the `devicePixelRatio` parameter passed to nanovg's `nvgBeginFrame()` function. The problem is caused by the `bgfx::setViewRect()` call defined in the `nvgRenderViewport()` function, as it should take size in consideration of the `devicePixelRatio` value.
However, this commit does not fix nanovg's example app because currently there is no easy way to pass the scale value to the `ExampleNanoVG::update()` method as it calls `nvgBeginFrame()`.
This commit moves the additional nanovg functions for bgfx to a separate header file, so it is possible to compile the original nanovg source files with bgfx in a custom build environment.
On Android when the application goes into the background, the EGL
window surface becomes invalid. It is possible to resume rendering when
coming to the foreground by resetting and reinitializing bgfx from
scratch, but this is costly in terms of performance.
This patch provides an alternative by letting the application provide a
new native window, causing bgfx to recreate just the EGL window surface
while keeping the EGL context intact. This allows the application to
resume rendering without needing to reload textures, shaders, etc.
To test, build and run the Hello World example on Android, switch to
another app and then back again. The screen should not remain blank
after switching back.
