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Date: Sun, 17 Jan 2021 10:30:23 +0100
Message-Id: <C8LBTLBQW1K8.3V5RLMYHVKR3F@testmac>
From: "Elias Naur" <mail@eliasnaur.com>
To: "Zhao Wang" <sunny.open@gmail.com>, <~eliasnaur/gio@lists.sr.ht>
Cc: 
Subject: Re: Injecting custom frame update to the flow?
References: <CAJJC9nfJDtirW3S8CA1FqtPYbPRSfem522dk2VNyJq1n0A-uaA@mail.gmail.com>
In-Reply-To: <CAJJC9nfJDtirW3S8CA1FqtPYbPRSfem522dk2VNyJq1n0A-uaA@mail.gmail.com>

On Sun Jan 17, 2021 at 8:33 AM CET, Zhao Wang wrote:
> Hi guys,
>
> I am trying to use gio to build a multi window chat client to have
> main chat UI in one
> window and run OpenGL ES game in another window which I hope to use Gio
> Window as well as the event loop and frame updating mechanism.
>
> The game has its own "drawFrame" method which calls standard OpenGL ES
> APIs.
> And does not use gio widgets yet (might need to add some later).
> I am wondering how I can inject the game's drawFrame into Gio window's
> frame
> update loop.
>
> I spent some time digging into the code, it looks to me current frame
> drawing happens
> in gio/gpu/GPU.Frame() method. So seems not possible without API
> changes.
> Is this true? If so, any advice on how to do this?
>

Is the game's OpenGL ES commands supposed to happen before, after, or in
between Gio drawing commands? If before or after, I believe you can use
the glfw example as inspiration. Specifically, use GLFW for the native
window and OpenGL context, and let both the game and Gio use the same
context. In the glfw example you can also see how the main program
forwards mouse/keyboard input to Gio. That's where you can route input
to the game as well.

A more portable variant is to use an OpenGL context for the game and a
separate context for Gio. If you bind a FBO with a texture target before
calling Gio's Frame, you can use the resulting texture to draw on top of
the game. This works because you can set up contexts so they share
resources (textures etc.) without sharing state.

If you haven't already considered it, I'd like to mention
https://github.com/ocornut/imgui. Imgui is immediate mode like Gio,
designed to be embedded, and used by many game studios for their GUI.

These are all high-level ideas. You'll probably hit various issues on
your way, all of which we're happy to help resolve. Portability is an
important Gio feature, and your embedding use case is an important kind
of portability.

Elias