This will be the returned egl configuration attribute for
EGL_BIND_TO_TEXTURE_TARGET_ANGLE once we transition to using the
Metal ANGLE backend directly.
By doing that we eliminate the need for the vertical flip flag.
As a side effect it fixes the bug when doing:
`canvasContext2d.drawImage(canvasWithWebGLContext, 0, 0);`
produced a flipped image because we didn't account for different origin
while serializing PaintingSurface into Gfx::Bitmap.
Visual progress on https://ciechanow.ski/curves-and-surfaces/
OpenGL's origin is at the bottom-left corner, while Skia's origin is at
the top-left corner. This change adds a transformation to compensate for
this difference when rendering PaintingSurface attached to WebGL
context.
For now only macOS is supported.
IOSurface is used as a backing store because it will allow us to read
it from Skia and write to it from OpenGL without any extra copying:
- ANGLE_metal_texture_client_buffer extension is used to create
EGLSurface from IOSurface.
- Then the same IOSurface is wrapped into Metal texture and passed to
Skia allowing to share the same memory between Skia Metal backend and
ANGLE.
