opengl tutorial 0

main.go

package main

import(
  "fmt"
  "gl"
  "gl/glu"
  "os"
  "sdl"
)

const (
  SCREEN_WIDTH=800
  SCREEN_HEIGHT=600
  SCREEN_BPP=32
)

var (
  surface *sdl.Surface
  t0 uint32
  frames uint32
)

func Quit(status int){
  sdl.Quit()
  os.Exit(status)
}

func ResizeWindow(width, height int){
  if height == 0 {
    height = 1
  }

  gl.Viewport(0,0,width,height)
  gl.MatrixMode(gl.PROJECTION)
  gl.LoadIdentity()

  aspect := float64(gl.GLfloat(width) / gl.GLfloat(height))

  var fov, near, far float64
  fov = 45.0
  near = 0.1
  far = 100.0
  glu.Perspective(fov, aspect, near, far)

  gl.MatrixMode(gl.MODELVIEW)
  gl.LoadIdentity()
}

func HandleKeyPress(keysym sdl.Keysym){
  switch keysym.Sym{
  case sdl.K_ESCAPE:
    Quit(0)
  case sdl.K_F1:
    sdl.WM_ToggleFullScreen(surface)
  }
}

func InitGL(){
  gl.ShadeModel(gl.SMOOTH)
  gl.ClearColor(0.0, 0.0, 0.0, 0.0)
  gl.ClearDepth(1.0)
  gl.Enable(gl.DEPTH_TEST)
  gl.DepthFunc(gl.LEQUAL)
  gl.Hint(gl.PERSPECTIVE_CORRECTION_HINT, gl.NICEST)
}

func DrawGLScene(){
  gl.Clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT)
  gl.LoadIdentity()
  sdl.GL_SwapBuffers()

  frames++
  t := sdl.GetTicks()
  if t-t0 >= 5000{
    seconds := (t-t0)/1000.0
    fps := frames / seconds
    fmt.Println(frames, "frames in", seconds, "seconds =", fps, "FPS")
    t0 = t
    frames = 0
  }
}

func main(){
  defer Quit(0) //At the end of this function, exit.

  if sdl.Init(sdl.INIT_VIDEO) < 0 {
    panic("Video Init failed: " + sdl.GetError())
  }

  videoFlags := uint32(sdl.OPENGL)
  videoFlags |= sdl.DOUBLEBUF
  videoFlags |= sdl.HWPALETTE

  surface = sdl.SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, videoFlags)

  if surface == nil {
    panic("Video mode not set: " + sdl.GetError())
    Quit(1)
  }

  sdl.GL_SetAttribute(sdl.GL_DOUBLEBUFFER, 1)

  InitGL()
  ResizeWindow(SCREEN_WIDTH,SCREEN_HEIGHT)

  running := true
  isActive := true
  event := &sdl.Event{}
  for running{
    for event.Poll(){
      switch event.Type{
      case sdl.ACTIVEEVENT:
        isActive = event.Active().Gain != 0
      case sdl.VIDEORESIZE:
        resize := event.Resize()
        width, height := int(resize.W), int(resize.H)
        surface = sdl.SetVideoMode(width, height, SCREEN_BPP, videoFlags)

        if surface == nil{
          fmt.Println("Could not form surface after Resize: " + sdl.GetError())
          Quit(1)
        }
        ResizeWindow(width,height)
      case sdl.KEYDOWN:
        HandleKeyPress(event.Keyboard().Keysym)
      case sdl.QUIT:
        running = false
      }
    }
    if isActive{
      DrawGLScene()
    }
  }
}