version 0.4.1. does not compile on Linux with Flutter 3.44.8

[RobertRoeb]

Hi,
I just tried to compile flutter_angle on Linux and there seems to have been a change in the texture API due to which flutter_angle does not compile. The current code in fl_angle_texture_gl.cc assumes 4 parameters for the populate method, but it now has *width and *height as well, so 6

static gboolean fl_angle_texture_gl_populate(
FlTextureGL *texture,
uint32_t *target,
uint32_t *name,
GError error
){
// std::cout << "attention: populate called" << std::endl;
FlAngleTextureGL f = (FlAngleTextureGL) texture;
*target = f->target;
*name = f->name;
return true;
}

[Knightro63]

Hi @RobertRoeb,

Linux has been very stubborn to work. I had it working then Flutter did an update and I have been trying to fix sense then.

My plan was to fix it last month but I have been a little busy. I am hoping to fix it soon.

Sorry for the inconvenience.

[RobertRoeb]

Hi there, I looked futher into it, although not finally successfully. I made it compile as per above. I then removed the gdk_window_create_gl_context() call as I think this is only for drawing directly into a GtkWidget, not a framebuffer. I then also added a call to eglMakeCurrent() after eglCreateContext() in flutter_angle_plugin.cc but that didn't help. What does not work is in _initRenderBuffer() the call to _rawOpenGl.glBindTexture(GL_TEXTURE_2D, rboId); which gives an getGlError() 1282 indicating that there is no current context. And also subsequent calls give that error. I am stuck here, unfortunately.

[RobertRoeb]

Just to be sure, I just tested the Windows version and it works fine. I still believe that Flutter on Linux steals the current OpenGL context.

[Knightro63]

Hi @RobertRoeb,

I have found the same issue. I can get the texture attach it to a frambuffer but the context is with it. So I am able to add my textures but then the whole screen is rotated or something else because Flutter is intercepting the context i believe.

[RobertRoeb]

I am not sure if you see a way to fix this, but I think we may need to create a hello_angle_flutter_linux world mini sample that reproduces the problem and file that as an issue on Flutter.dev. It might get refused as "not our business", but then noone will ever be able to use OpenGL in a Flutter app on Linux. Maybe there is a Texture widget example that I can use a start. Could you make a mini release so that flutter_angle compiles again on Linux, even if it currently does not run correctly?

[RobertRoeb]

I got it now by asking a smart computer: To render using the ANGLE library (OpenGL ES) into Flutter's Texture widget on Linux, you leverage Flutter's native FlTextureGL class. Because the Flutter Linux embedder already initializes and exposes a valid OpenGL/OpenGL ES rendering context during the populate_texture callback, you do not need to initialize a separate EGL window or ANGLE context manually. Instead, you can directly execute standard OpenGL ES pipeline calls (such as compiling GLES shaders and dispatching vertex arrays) straight to the active framebuffer.

[Knightro63]

Hi @RobertRoeb,

Yes, this is currently what the ANGLE linux is doing. It is using native OpenGL calls. The problem becomes getting the FlTexture to bind properly to the vertex buffers or frame buffer. I have been able to get something on the screen but not the correct thing has been the issue.

[RobertRoeb]

The current code creates an EGL context - I think it shouldn't be done spefically on Flutter Linux as it is already there.

#include "include/angle_texture_plugin/angle_texture_plugin.h"
#include <flutter_linux/flutter_linux.h>
#include <gtk/gtk.h>
#include <epoxy/gl.h>

#define ANGLE_TEXTURE_PLUGIN(obj)
(G_TYPE_CHECK_INSTANCE_CAST((obj), angle_texture_plugin_get_type(), AngleTexturePlugin))

struct _AngleTexturePlugin {
GObject parent_instance;
FlTextureRegistrar* texture_registrar;
};

G_DEFINE_TYPE(AngleTexturePlugin, angle_texture_plugin, g_object_get_type())

// 1. Define our custom Texture object
#define ANGLE_FL_TEXTURE(obj)
(G_TYPE_CHECK_INSTANCE_CAST((obj), angle_fl_texture_get_type(), AngleFlTexture))

typedef struct _AngleFlTexture {
FlTextureGL parent_instance;
GLuint fbo;
GLuint resolved_texture_id;
} AngleFlTexture;

G_DEFINE_TYPE(AngleFlTexture, angle_fl_texture, fl_texture_gl_get_type())

static void angle_fl_texture_init(AngleFlTexture* self) {
}

// 2. The Render loop processing logic passed into Flutter
static gboolean angle_fl_texture_populate_texture(FlTextureGL* texture,
uint32_t* target,
uint32_t* name,
uint32_t* width,
uint32_t* height,
GError** error) {
AngleFlTexture* self = ANGLE_FL_TEXTURE(texture);

*width = 400;
*height = 400;
*target = GL_TEXTURE_2D;

if (not yet initiliazed)
// Generate offscreen frame binding target, TODO elsewhere
glGenFramebuffers(1, &self->fbo);
glGenTextures(1, &self->resolved_texture_id);
}

// Allocate/re-bind the render destination texture asset texture target
glBindTexture(GL_TEXTURE_2D, self->resolved_texture_id);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, *width, *height, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

// Bind offscreen Framebuffer context
glBindFramebuffer(GL_FRAMEBUFFER, self->fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, self->resolved_texture_id, 0);

// Return the texture parameters back to Flutter engine compositor
*name = self->resolved_texture_id;

// render here

// Unbind structures safely to prevent pipeline leaks
glBindFramebuffer(GL_FRAMEBUFFER, 0);
return TRUE;
}

static void Angle_fl_texture_dispose(GObject* object) {
AngleFlTexture* self = ANGLE_FL_TEXTURE(object);
glDeleteFramebuffers(1, &self->fbo);
glDeleteTextures(1, &self->resolved_texture_id);
G_OBJECT_CLASS(angle_fl_texture_parent_class)->dispose(object);
}

static void angle_fl_texture_class_init(AngleFlTextureClass* klass) {
FL_TEXTURE_GL_CLASS(klass)->populate_texture = angle_fl_texture_populate_texture;
G_OBJECT_CLASS(klass)->dispose = angle_fl_texture_dispose;
}

// 3. Platform method router execution handler
static void angle_texture_plugin_handle_method_call(
AngleTexturePlugin* self,
FlMethodCall* method_call) {
g_autoptr(FlMethodResponse) response = nullptr;
const gchar* method = fl_method_call_get_name(method_call);

if (strcmp(method, "createAngleTexture") == 0) {
AngleFlTexture* texture = ANGLE_FL_TEXTURE(g_object_new(angle_fl_texture_get_type(), nullptr));
fl_texture_registrar_register_texture(self->texture_registrar, FL_TEXTURE(texture));

int64_t texture_id = fl_texture_get_id(FL_TEXTURE(texture));
fl_texture_registrar_mark_texture_frame_available(self->texture_registrar, FL_TEXTURE(texture));

g_autoptr(FlValue) result = fl_value_new_int(texture_id);
response = FL_METHOD_RESPONSE(fl_method_success_response_new(result));

} else {
response = FL_METHOD_RESPONSE(fl_method_not_implemented_response_new());
}
fl_method_call_respond(method_call, response, nullptr);
}

static void angle_texture_plugin_dispose(GObject* object) {
G_OBJECT_CLASS(angle_texture_plugin_parent_class)->dispose(object);
}

static void angle_texture_plugin_class_init(AngleTexturePluginClass* klass) {
G_OBJECT_CLASS(klass)->dispose = angle_texture_plugin_dispose;
}

static void angle_texture_plugin_init(AngleTexturePlugin* self) {}

static void method_call_cb(FlMethodChannel* channel, FlMethodCall* method_call, gpointer user_data) {
AngleTexturePlugin* plugin = ANGLE_TEXTURE_PLUGIN(user_data);
angle_texture_plugin_handle_method_call(plugin, method_call);
}

void angle_texture_plugin_register_with_registrar(FlPluginRegistrar* registrar) {
AngleTexturePlugin* plugin = ANGLE_TEXTURE_PLUGIN(g_object_new(angle_texture_plugin_get_type(), nullptr));
plugin->texture_registrar = fl_plugin_registrar_get_texture_registrar(registrar);

g_autoptr(FlStandardMethodCodec) codec = fl_standard_method_codec_new();
g_autoptr(FlMethodChannel) channel = fl_method_channel_new(
fl_plugin_registrar_get_messenger(registrar), "angle_texture_plugin", FL_METHOD_CODEC(codec));

fl_method_channel_set_method_call_handler(channel, method_call_cb, g_object_ref(plugin), g_object_unref);
g_object_unref(plugin);
}

[RobertRoeb]

Put differently, I think you have to remove (or not use) all the eGL code under Linux.

[Knightro63]

Hi @RobertRoeb,

I will take a look at it this weekend.