// Copyright 2020 The Ebiten Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package graphicscommand

var theThread Thread

type Thread interface {
	Call(f func())
}

// SetRenderingThread must be called from the rendering thread where e.g. OpenGL works.
//
// TODO: Create thread in this package instead of setting it externally.
func SetRenderingThread(thread Thread) {
	theThread = thread
}

// runOnRenderingThread calls f on the rendering thread, and returns an error if any.
func runOnRenderingThread(f func()) {
	// The thread is nil when 1) GOOS=js or 2) using golang.org/x/mobile/gl.
	// When golang.org/x/mobile/gl is used, all the GL functions are called via Context, which already runs on an
	// appropriate thread.
	if theThread == nil {
		f()
		return
	}
	theThread.Call(f)
}