Add support for external OpenGL textures

[pchampio]

The flutter engine ABI supports external OpenGL textures allowing the embedder to draw to OpenGL directly. engine#7087

It's needed to implement the VideoPlayer.

[ghost]

Will also be useful for doing 3D graphics and webrtc.

[cloudwebrtc]

@Drakirus @gedw99
I have done a texture patch on flutter/engine based on GLFW, it seems to work very well, but I don't know how to port to go-flutter, here is my Texture rendering code, maybe it will help you.
https://github.com/cloudwebrtc/flutter-engine/blob/texture_for_glfw/shell/platform/glfw/external_texture_gl.cc

[pchampio]

Hi @cloudwebrtc I'm seeing progress on flutter/engine about the textureAPI 👍.
I'm trying to implement the textureAPI for go-flutter based your CPP code.

While implementing the API, I hit a wall.

My understanding was that you register a texture using: FlutterEngineRegisterExternalTexture, then mark a new frame with FlutterDesktopMarkExternalTextureFrameAvailable. At some point, in between or after those calls, the flutter-engine calls you back using the gl_external_texture_frame_callback. My issue is that gl_external_texture_frame_callback NEVER gets called.
Am my missing something?
Here is my progress on the implementation: commit

[cloudwebrtc]

@Drakirus Sorry to reply so late, I see you in the code RegisterExternalTexture(textureId: 400), and after a while MarkExternalTextureFrameAvailable(textureId: 600), this place textureId should be a fixed value of int64_t when registering once, for example: textureId = 0, when your The plugin generates a new video frame, only need to execute MarkExternalTextureFrameAvailable(texture: 0), then the flutter engine will call GLExternalTextureFrameCallback(texture: 0, ...).

frameI := int64(0)
for !a.window.ShouldClose() {
    frameI++
    glfw.WaitEventsTimeout(0.016) // timeout to get 60fps-ish iterations			
    if frameI == 400 {
        print("REGISTER: ")
        print(a.engine.RegisterExternalTexture(frameI))
    }
    if frameI == 600 {
        print("New Frame: ")
        print(a.engine.MarkExternalTextureFrameAvailable(frameI))
    }

change to:

frameI := int64(0)
textureId := int64(0)
print(a.engine.RegisterExternalTexture(textureId))
for !a.window.ShouldClose() {
    frameI++
    glfw.WaitEventsTimeout(0.016) // timeout to get 60fps-ish iterations			
    print("New Frame: ")
    print(a.engine.MarkExternalTextureFrameAvailable(textureId))

[pchampio]

@cloudwebrtc Thanks for your reply!
The testing code that I pushed was wrong, I've updated it: commit.

I'm still facing the same issue: gl_external_texture_frame_callback never gets called. 😞

I've updated the code to use a bare C handler code, OnAcquireExternalTexture never get called.

The terminal output looks great:

[....]
Texture: register result: true
go-flutter: no handler found for channel flutter/isolate
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
Texture: New Frame result: true
go-flutter: closing application

[cloudwebrtc]

@Drakirus Your changes are correct, just add Texture(textureId: 1) to flutter lib/main.dart.

            child: Container(
              color: Colors.lightBlueAccent,
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Texture(textureId: 1),
                  Text('You have pointed at this box this many times:'),
                  Text(
                    '$_enterCounter Entries\n$_exitCounter Exits',
                    style: Theme.of(context).textTheme.display1,
                  ),
                  Text(
                    'The cursor is here: (${x.toStringAsFixed(2)}, ${y.toStringAsFixed(2)})',
                  ),
                ],
              ),
            ),

I tested it under linux, OnAcquireExternalTexture is called.

[ERROR:flutter/shell/platform/embedder/embedder.cc(578)] Could not create external texture.
=== OnAcquireExternalTexture: 1
Unknown pixel config 0x0
[ERROR:flutter/shell/platform/embedder/embedder.cc(578)] Could not create external texture.
=== OnAcquireExternalTexture: 1
Unknown pixel config 0x0
[ERROR:flutter/shell/platform/embedder/embedder.cc(578)] Could not create external texture.
=== OnAcquireExternalTexture: 1
Unknown pixel config 0x0
[ERROR:flutter/shell/platform/embedder/embedder.cc(578)] Could not create external texture.
=== OnAcquireExternalTexture: 1
Unknown pixel config 0x0
[ERROR:flutter/shell/platform/embedder/embedder.cc(578)] Could not create external texture.
=== OnAcquireExternalTexture: 1
Unknown pixel config 0x0
[ERROR:flutter/shell/platform/embedder/embedder.cc(578)] Could not create external texture.
Texture: New Frame result: true
=== OnAcquireExternalTexture: 1
Unknown pixel config 0x0
[ERROR:flutter/shell/platform/embedder/embedder.cc(578)] Could not create external texture.
go-flutter: closing application

[pchampio]

Texture(textureId: 1) that what I was missing, Thanks!!

[pchampio]

Making progress:

A demo is available at: https://github.com/go-flutter-desktop/examples/tree/feature/gl_texture/texture_tutorial, use hover run -b '@beta' to try it out.

@cloudwebrtc everything was implemented thanks to you, big thanks!

[cloudwebrtc]

Wow, that's awesome.

[pchampio]

Updated the demo. Added an very simple videoplayer

[pchampio]

fix taged in tag: v0.29.0