Gio + OpenGL Core Reproducing Program

main.go

// SPDX-License-Identifier: Unlicense OR MIT

// GLFW doesn't build on OpenBSD and FreeBSD.
//go:build !openbsd && !freebsd && !android && !ios && !js
// +build !openbsd,!freebsd,!android,!ios,!js

// The glfw example demonstrates integration of Gio into a foreign
// windowing and rendering library, in this case GLFW
// (https://www.glfw.org).
//
// See the go-glfw package for installation of the native
// dependencies:
//
// https://github.com/go-gl/glfw
package main

import (
	"image"
	"log"
	"runtime"
	"time"

	"gioui.org/font/gofont"
	"gioui.org/gpu"
	"gioui.org/io/input"
	"gioui.org/layout"
	"gioui.org/op"
	"gioui.org/text"
	"gioui.org/unit"
	"gioui.org/widget"
	"gioui.org/widget/material"
	"github.com/go-gl/gl/v3.3-core/gl"
	"github.com/go-gl/glfw/v3.3/glfw"
)

func main() {
	// Required by the OpenGL threading model.
	runtime.LockOSThread()

	err := glfw.Init()
	if err != nil {
		log.Fatal(err)
	}
	defer glfw.Terminate()
	// Gio assumes a sRGB backbuffer.
	glfw.WindowHint(glfw.SRGBCapable, glfw.True)
	glfw.WindowHint(glfw.ScaleToMonitor, glfw.True)
	glfw.WindowHint(glfw.CocoaRetinaFramebuffer, glfw.True)
	glfw.WindowHint(glfw.ContextVersionMajor, 3)
	glfw.WindowHint(glfw.ContextVersionMinor, 3)
	glfw.WindowHint(glfw.OpenGLProfile, glfw.OpenGLCoreProfile)
	glfw.WindowHint(glfw.OpenGLForwardCompatible, glfw.True)

	window, err := glfw.CreateWindow(800, 600, "Gio + GLFW", nil, nil)
	if err != nil {
		log.Fatal(err)
	}

	window.MakeContextCurrent()

	if err := gl.Init(); err != nil {
		log.Fatalf("gl.Init failed: %v", err)
	}
	// Enable sRGB.
	gl.Enable(gl.FRAMEBUFFER_SRGB)
	// Set up default VBA, required for the forward-compatible core profile.
	var defVBA uint32
	gl.GenVertexArrays(1, &defVBA)
	gl.BindVertexArray(defVBA)

	var queue input.Router
	var ops op.Ops
	th := material.NewTheme()
	th.Shaper = text.NewShaper(text.WithCollection(gofont.Collection()))
	gpuCtx, err := gpu.New(gpu.OpenGL{ES: false, Shared: true})
	if err != nil {
		log.Fatal(err)
	}
	defer gpuCtx.Release()

	for !window.ShouldClose() {
		glfw.PollEvents()
		scale, _ := window.GetContentScale()
		width, height := window.GetFramebufferSize()
		sz := image.Point{X: width, Y: height}
		ops.Reset()
		gtx := layout.Context{
			Ops:    &ops,
			Now:    time.Now(),
			Source: queue.Source(),
			Metric: unit.Metric{
				PxPerDp: scale,
				PxPerSp: scale,
			},
			Constraints: layout.Exact(sz),
		}
		drawOpenGL()
		draw(gtx, th)
		gpuCtx.Frame(gtx.Ops, gpu.OpenGLRenderTarget{}, sz)
		queue.Frame(gtx.Ops)
		window.SwapBuffers()
	}
}

var (
	button widget.Clickable
	green  float64 = 0.2
)

// drawOpenGL demonstrates the direct use of OpenGL commands
// to draw non-Gio content below the Gio UI.
func drawOpenGL() {
	gl.ClearColor(0, float32(green), 0, 1)
	gl.Clear(gl.COLOR_BUFFER_BIT)
}

func draw(gtx layout.Context, th *material.Theme) layout.Dimensions {
	return layout.Center.Layout(gtx,
		material.Button(th, &button, "Button").Layout,
	)
}