Make egui_glow painter to work on web

[KentaTheBugMaker]

I made PR #852 but this way affect many points.
These my works

• eliminate glutin dependency from painter
• port PostProcess for sRGB correct color for web from egui_web painter
• eliminate VAO by emulating VAO
• add feature flag painter_only to reuse glow painter
• implement egui_web::Painter trait for wrapped glow painter
• share GLSL ES and GLSL shader
  Current tested platforms
• OpenGL 4.6 (Ryzen 5 5500U with AMD proprietary windows driver) (not tested but coded to work 2.0 or above)
• WebGL2 (firefox android , MS edge)
• WebGL1+sRGB (WebGL2 disabled firefox)
• WebGL1 (servo nightly build)

[KentaTheBugMaker]

I monitored by Spector.js and found glow painter 's draw call is half of egui_web.
which means lower CPU usage,lower power consumption,higher frame rate.

• glow painter 132
• webgl2 painter 269

[emilk]

This looks really promising, nice work!

[parasyte]

This is nitpicky, but I think it would make sense to offer two constructors here instead of one.

Suggested change

	pub(crate) unsafe fn new(gl: &glow::Context, is_native_vao: bool) -> Self {
	if is_native_vao {
	Self::Native(gl.create_vertex_array().unwrap())
	} else {
	Self::Emulated(crate::vao_emulate::EmulatedVao::new())
	}
	}
	pub(crate) unsafe fn native(gl: &glow::Context) -> Self {
	Self::Native(gl.create_vertex_array().unwrap())
	}
	pub(crate) fn emulated() -> Self {
	Self::Emulated(crate::vao_emulate::EmulatedVao::new())
	}

Also, wouldn't the API be nicer if the constructor captured the &glow::Context here so it doesn't need to be passed to the other methods? That might also help reduce some confusion about why VAO::bind_vertex_array is unsafe, but the others are not?

[emilk]

Good point about two constructors 👍

Capturing &glow::Context leads to a lot of ugly lifetime issues. Passing it in by reference is also more explicit, i.e. easier to see what is actually doing graphics calls. This was discussed in the original glow PR.

[KentaTheBugMaker]

Ok i will split constructor.
but is there good way to switch emulated mode?

[parasyte]

Capturing &glow::Context leads to a lot of ugly lifetime issues. Passing it in by reference is also more explicit, i.e. easier to see what is actually doing graphics calls. This was discussed in the original glow PR.

Ok! Good to know, I didn't follow that conversation closely.

Ok i will split constructor.
but is there good way to switch emulated mode?

This question implies there is a way to switch the emulation mode with just one constructor? I don't believe that is the case before or after the suggested patch.

[KentaTheBugMaker]

I thought this procedure good enough to switch emulated mode .
Is there any suggestion?

[emilk]

There is a lot of things that needs testing with "Color test":

• Native glow
• Web glow on WebGL2
• Web glow on WebGL1 with sRGBA
• Web glow on WebGL1 without sRGBA (won't pass the color test, but should look as good as the current WebGL painter)

[KentaTheBugMaker]

merging upstream change
Now i post some good photo

.

[emilk]

Thanks @t18b219k - great work!

[AlexApps99]

Sorry I didn't have much feedback for it - busy with exams, I won't be able to contribute much for a bit.