Vertex shader that passes color information to fragment shader.

multiparam.go

package main

import (
	"fmt"
	"runtime"

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

const (
	vertex = `#version 330

in vec4 position;
in vec4 color;

smooth out vec4 base_color;

void main()
{
    gl_Position = position;
    base_color  = color;
}`

	fragment = `#version 330

smooth in vec4 base_color;
out vec4 frag_color;

void main()
{
	frag_color = base_color;
}`
)

type Object struct {
	vao gl.VertexArray
	vbo gl.Buffer
	pos gl.AttribLocation
	col gl.AttribLocation
}

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(program.GetFragDataLocation("frag_color"), "frag_color")
	program.Link()
	program.Use()
	defer program.Delete()

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

	// Objects

	verticies1 := []float32{
		0, 0, 0, 1,
		0, 1, 0, 1,
		1, 1, 0, 1,
		1, 0, 0, 1,
		0, 1, 0, 1,
		0, 0, 1, 1}
	verticies2 := []float32{
		-1, -1, 0, 1,
		-1, 0, 0, 1,
		0, 0, 0, 1,
		1, 0, 0, 1,
		1, 0, 0, 1,
		1, 0, 0, 1}

	o1, _ := NewObject(program, verticies1)
	o2, _ := NewObject(program, verticies2)

	// Main loop.

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

		o1.Draw()
		o2.Draw()

		window.SwapBuffers()
		glfw.PollEvents()

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

func NewObject(program gl.Program, verticies []float32) (*Object, error) {
	vao := gl.GenVertexArray()
	vao.Bind()

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

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

	pos := program.GetAttribLocation("position")
	pos.AttribPointer(4, gl.FLOAT, false, 0, nil)

	col := program.GetAttribLocation("color")
	col.AttribPointer(4, gl.FLOAT, false, 0, uintptr(48))

	vbo.Unbind(gl.ARRAY_BUFFER)
	vao.Unbind()

	return &Object{
		vao: vao,
		vbo: vbo,
		pos: pos,
		col: col,
	}, nil
}

func (o *Object) Draw() {
	o.vao.Bind()
	o.pos.EnableArray()
	o.col.EnableArray()
	gl.DrawArrays(gl.TRIANGLES, 0, 3)
	o.col.DisableArray()
	o.pos.DisableArray()
	o.vao.Unbind()
}