Modern OpenGL to draw using multiple Vertex Attribute Objects.

twotriangles.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.

package main

import (
	"fmt"
	"runtime"

	"github.com/go-gl/gl"
	glfw "github.com/go-gl/glfw3"
)

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() {
	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()

	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()

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

	// VAO 1

	vao1 := gl.GenVertexArray()
	vao1.Bind()

	vbo1 := gl.GenBuffer()
	vbo1.Bind(gl.ARRAY_BUFFER)

	verticies1 := []float32{0, 0, 0, 0, 1, 0, 1, 1, 0}
	gl.BufferData(gl.ARRAY_BUFFER, len(verticies1)*4, verticies1, gl.STATIC_DRAW)

	// Implicitly affects the previously bound object,
	// in this case vbo1.
	pa1 := program.GetAttribLocation("position")
	pa1.AttribPointer(3, gl.FLOAT, false, 0, nil)
	pa1.EnableArray()
	defer pa1.DisableArray()

	vao1.Unbind()

	// VAO 2

	vao2 := gl.GenVertexArray()
	vao2.Bind()

	vbo2 := gl.GenBuffer()
	vbo2.Bind(gl.ARRAY_BUFFER)

	verticies2 := []float32{-1, -1, 0, -1, 0, 0, 0, 0, 0}
	gl.BufferData(gl.ARRAY_BUFFER, len(verticies2)*4, verticies2, gl.STATIC_DRAW)

	// Implicitly affects the previously bound object,
	// in this case vbo2.
	pa2 := program.GetAttribLocation("position")
	pa2.AttribPointer(3, gl.FLOAT, false, 0, nil)
	pa2.EnableArray()
	defer pa2.DisableArray()

	vao2.Unbind()

	// Main loop.

	for !window.ShouldClose() {
		gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)

		vao1.Bind()
		gl.DrawArrays(gl.TRIANGLES, 0, 3)
		vao1.Unbind()

		vao2.Bind()
		gl.DrawArrays(gl.TRIANGLES, 0, 3)
		vao2.Unbind()

		window.SwapBuffers()
		glfw.PollEvents()

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