OpenGl stops working properly as soon as I try to use goroutines. This piece of code rotates triangle on the screen with OpenGl. I wrote several main loops: * one that uses time.Ticker to control the framerate, * one that listens to SDL events through a channel to know when to stop the program, * one that does both, * and one that does neither (…

opengl_vs_goroutines.go

package main

import (
	"fmt"
	"github.com/0xe2-0x9a-0x9b/Go-SDL/sdl"
	gl "github.com/chsc/gogl/gl33"
	"math"
	"runtime"
	"time"
	"unsafe"
)

const DEG_TO_RAD = math.Pi / 180

type GoMatrix [16]float64
type GlMatrix [16]gl.Float

var good_frames, bad_frames, sdl_events int

func main() {
	runtime.GOMAXPROCS(1)
	//=========================================================================
	// Just opening a window, skip to the next part.

	if status := sdl.Init(sdl.INIT_VIDEO); status != 0 {
		panic("Could not initialize SDL: " + sdl.GetError())
	}
	defer sdl.Quit()

	sdl.GL_SetAttribute(sdl.GL_DOUBLEBUFFER, 1)
	const FLAGS = sdl.OPENGL
	if screen := sdl.SetVideoMode(640, 480, 32, FLAGS); screen == nil {
		panic("Could not open SDL window: " + sdl.GetError())
	}

	if err := gl.Init(); err != nil {
		panic(err)
	}

	gl.Viewport(0, 0, 640, 480)
	gl.ClearColor(.5, .5, .5, 1)
	renderer := gl.GetString(gl.RENDERER)
	fmt.Println(gl.GoStringUb(renderer))

	//=========================================================================
	// Simplest shaders ever.

	// A matrix to move the model, nothing else.
	vertex_code := gl.GLString(`
	#version 330 core
    in vec3 vpos;
    uniform mat4 MVP;
    void main() { 
        gl_Position = MVP * vec4(vpos, 1);
    }	
	`)
	// Everything is red.
	fragment_code := gl.GLString(`
	#version 330 core
    void main(){
        gl_FragColor = vec4(1,0,0,1);
    }
	`)
	vs := gl.CreateShader(gl.VERTEX_SHADER)
	fs := gl.CreateShader(gl.FRAGMENT_SHADER)
	gl.ShaderSource(vs, 1, &vertex_code, nil)
	gl.ShaderSource(fs, 1, &fragment_code, nil)
	gl.CompileShader(vs)
	gl.CompileShader(fs)
	prog := gl.CreateProgram()
	gl.AttachShader(prog, vs)
	gl.AttachShader(prog, fs)
	gl.LinkProgram(prog)
	// Did it compile?
	var link_status gl.Int
	gl.GetProgramiv(prog, gl.LINK_STATUS, &link_status)
	if link_status == gl.FALSE {
		var info_log_length gl.Int
		gl.GetProgramiv(prog, gl.INFO_LOG_LENGTH, &info_log_length)
		if info_log_length == 0 {
			panic("Program linking failed but OpenGL has no log about it.")
		} else {
			info_log_gl := gl.GLStringAlloc(gl.Sizei(info_log_length))
			defer gl.GLStringFree(info_log_gl)
			gl.GetProgramInfoLog(prog, gl.Sizei(info_log_length), nil, info_log_gl)
			info_log := gl.GoString(info_log_gl)
			panic(info_log)
		}
	}
	gl.UseProgram(prog)
	attrib_vpos := gl.Uint(gl.GetAttribLocation(prog, gl.GLString("vpos")))

	//=========================================================================
	// One triangle.

	positions := [...]gl.Float{-.5, -.5, 0, .5, -.5, 0, 0, .5, 0}

	var vao gl.Uint
	gl.GenVertexArrays(1, &vao)
	gl.BindVertexArray(vao)

	var vbo gl.Uint
	gl.GenBuffers(1, &vbo)
	gl.BindBuffer(gl.ARRAY_BUFFER, vbo)
	gl.BufferData(gl.ARRAY_BUFFER,
		gl.Sizeiptr(unsafe.Sizeof(positions)),
		gl.Pointer(&positions[0]),
		gl.STATIC_DRAW)

	gl.EnableVertexAttribArray(attrib_vpos)
	gl.VertexAttribPointer(attrib_vpos, 3, gl.FLOAT, gl.FALSE, 0, gl.Pointer(nil))

	//=========================================================================
	gl.Finish()
	LoopNothing(prog)
	fmt.Println("Good frames", good_frames)
	fmt.Println("Bad frames", bad_frames)
	fmt.Println("sdl events", sdl_events)
}

func LoopSdlTick(program gl.Uint) {
	start_time := time.Now()
	ticker := time.NewTicker(1000 * time.Millisecond)
	defer ticker.Stop()
	running := true
	for running {
		select {
		case tick_time := <-ticker.C:
			OnTick(start_time, tick_time, program)
		case event := <-sdl.Events:
			running = OnSdlEvent(event)
		}
	}
}

func DummyFeeder(dummy_chan chan int) {
	for {
		dummy_chan <- 0
		//		time.Sleep(1 * time.Millisecond)
		//		runtime.Gosched()
	}
}

func LoopNothing(program gl.Uint) {
	start_time := time.Now()
	stop_time := start_time.Add(time.Duration(10 * time.Second))
	//	dummy_chan := make(chan int)
	//	go DummyFeeder(dummy_chan)
	running := true
	for running {
		//		select {
		//		case <-dummy_chan:
		//		default:
		//			break
		//		}
		tick_time := time.Now()
		OnTick(start_time, tick_time, program)
		time.Sleep(20 * time.Millisecond)
		if tick_time.After(stop_time) {
			running = false
		}
	}
}

func LoopTick(program gl.Uint) {
	start_time := time.Now()
	stop_time := start_time.Add(time.Duration(10 * time.Second))
	ticker := time.NewTicker(20 * time.Millisecond)
	defer ticker.Stop()
	running := true
	for running {
		select {
		case tick_time := <-ticker.C:
			{
				OnTick(start_time, tick_time, program)
				tick_time := time.Now()
				if tick_time.After(stop_time) {
					running = false
				}
			}
		default:
			runtime.Gosched()
		}
	}
}

func LoopSdl(program gl.Uint) {
	var now time.Time
	start_time := time.Now()
	time_next := start_time.Add(time.Duration(20 * time.Millisecond))
	running := true
	for running {
		select {
		case e := <-sdl.Events:
			running = OnSdlEvent(e)
		default:
			break
		}
		now = time.Now()
		if now.After(time_next) {
			OnTick(start_time, now, program)
			time_next = now.Add(time.Duration(20 * time.Millisecond))
		} else {
			time.Sleep(1 * time.Millisecond)
		}
	}
}

func OnSdlEvent(event interface{}) bool {
	sdl_events++
	switch event.(type) {
	case sdl.QuitEvent:
		return false // Stop the main loop.
	}
	return true // Do not stop the main loop.
}

func OnTick(start_time, tick_time time.Time, program gl.Uint) {
	duration := tick_time.Sub(start_time).Seconds()
	speed := 10.
	angle := math.Mod(duration*speed, 360)
	gom := RotZ(angle)
	MVP := ToGlMatrix(gom)

	matrix_loc := gl.GetUniformLocation(program, gl.GLString("MVP"))
	dummy_matrix_loc := gl.GetUniformLocation(program, gl.GLString("dummy"))
	if gl.GetError() != gl.NO_ERROR {
		fmt.Println("Error get location") // Never happens.
	}
	if dummy_matrix_loc == -1 {
		good_frames++ // Because it SHOULD fail.
	} else {
		bad_frames++ // That's not normal.
	}
	gl.UniformMatrix4fv(matrix_loc, 16, gl.TRUE, &MVP[0])
	if gl.GetError() != gl.NO_ERROR {
		fmt.Println("Error send matrix") // Never happens.
	}
	gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
	if gl.GetError() != gl.NO_ERROR {
		fmt.Println("Error clearing") // Never happens.
	}
	gl.DrawArrays(gl.TRIANGLES, 0, 3)
	if gl.GetError() != gl.NO_ERROR {
		fmt.Println("Error drawing") // Never happens.
	}
	sdl.GL_SwapBuffers()
}

func RotZ(angle float64) GoMatrix {
	var gom GoMatrix
	a := angle * DEG_TO_RAD
	c := math.Cos(a)
	s := math.Sin(a)
	gom[0] = c
	gom[1] = s
	gom[4] = -s
	gom[5] = c
	gom[10] = 1
	gom[15] = 1
	return gom
}

func ToGlMatrix(gom GoMatrix) GlMatrix {
	var glm GlMatrix
	glm[0] = gl.Float(gom[0])
	glm[1] = gl.Float(gom[1])
	glm[2] = gl.Float(gom[2])
	glm[3] = gl.Float(gom[3])
	glm[4] = gl.Float(gom[4])
	glm[5] = gl.Float(gom[5])
	glm[6] = gl.Float(gom[6])
	glm[7] = gl.Float(gom[7])
	glm[8] = gl.Float(gom[8])
	glm[9] = gl.Float(gom[9])
	glm[10] = gl.Float(gom[10])
	glm[11] = gl.Float(gom[11])
	glm[12] = gl.Float(gom[12])
	glm[13] = gl.Float(gom[13])
	glm[14] = gl.Float(gom[14])
	glm[15] = gl.Float(gom[15])
	return glm
}