With DirectX, the graphics driver cannot be determined until the
main loop starts, as a transparent window cannot be treated with
DirectX so far. On the other hand, compiling shaders requires a
graphics driver as it requires information about Y directions of
NDCs and framebuffers.
This change delays compiling shaders until the graphics commands
are actually executed in the main loop.
Updates #1007
Updates #2019
This is necessary to remove the graphics driver usage from
(*ebiten.Image).At. And this is necessary to determine the graphics
driver after the window becomes transparent or not.
Unfortunately, it is not obvious to make a transparent window with
DirectX. Then, the determination of a graphics driver should be delayed.
Updates #1007
If regions by ReplacePixel are overlapped, this can panics. This can
happen only on Android, where a context lost can happen.
Thus, a sub-image cannot call a direct ReplacePixels. internal/buffer
has to care this.
