main.go

// Copyright 2014 The go-gl Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Originally put together by github.com/segfault88, but
// I thought it might be useful to somebody else too.

// It took me quite a lot of frustration and messing around
// to get a basic example of glfw3 with modern OpenGL (3.3)
// with shaders etc. working. Hopefully this will save you
// some trouble. Enjoy!

package main

import (
	"fmt"
	"github.com/go-gl/gl"
	glfw "github.com/go-gl/glfw3"
	"github.com/go-gl/glu"
	"runtime"
)

const (
	vertex = `#version 330

in vec2 position;

void main()
{
    gl_Position = vec4(position, 0.0, 1.0);
}`

	fragment = `#version 330

out vec4 outColor;

void main()
{
    outColor = vec4(1.0, 1.0, 1.0, 1.0);
}`
)

func main() {
	// lock glfw/gl calls to a single thread
	runtime.LockOSThread()

	glfw.Init()
	defer glfw.Terminate()

	glfw.WindowHint(glfw.ContextVersionMajor, 3)
	glfw.WindowHint(glfw.ContextVersionMinor, 3)
	glfw.WindowHint(glfw.OpenglForwardCompatible, glfw.True)
	glfw.WindowHint(glfw.OpenglProfile, glfw.OpenglCoreProfile)

	window, err := glfw.CreateWindow(800, 600, "Example", nil, nil)
	if err != nil {
		panic(err)
	}

	defer window.Destroy()

	window.MakeContextCurrent()
	glfw.SwapInterval(1)

	gl.Init()

	vao := gl.GenVertexArray()
	vao.Bind()

	vbo := gl.GenBuffer()
	vbo.Bind(gl.ARRAY_BUFFER)

	verticies := []float32{0, 1, 0, -1, -1, 0, 1, -1, 0}

	gl.BufferData(gl.ARRAY_BUFFER, len(verticies)*4, verticies, gl.STATIC_DRAW)

	vertex_shader := gl.CreateShader(gl.VERTEX_SHADER)
	vertex_shader.Source(vertex)
	vertex_shader.Compile()
	fmt.Println(vertex_shader.GetInfoLog())
	defer vertex_shader.Delete()

	fragment_shader := gl.CreateShader(gl.FRAGMENT_SHADER)
	fragment_shader.Source(fragment)
	fragment_shader.Compile()
	fmt.Println(fragment_shader.GetInfoLog())
	defer fragment_shader.Delete()

	program := gl.CreateProgram()
	program.AttachShader(vertex_shader)
	program.AttachShader(fragment_shader)

	program.BindFragDataLocation(0, "outColor")
	program.Link()
	program.Use()
	defer program.Delete()

	positionAttrib := program.GetAttribLocation("position")
	positionAttrib.AttribPointer(3, gl.FLOAT, false, 0, nil)
	positionAttrib.EnableArray()
	defer positionAttrib.DisableArray()

	gl.ClearColor(0.3, 0.3, 0.3, 1.0)

	for !window.ShouldClose() {
		gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
		gl.DrawArrays(gl.TRIANGLES, 0, 3)

		window.SwapBuffers()
		glfw.PollEvents()

		if window.GetKey(glfw.KeyEscape) == glfw.Press {
			window.SetShouldClose(true)
		}
	}
}

func checkGLerror() {
	if glerr := gl.GetError(); glerr != gl.NO_ERROR {
		string, _ := glu.ErrorString(glerr)
		panic(string)
	}
}