gl21-cube: Cube in demo appears squashed. about example HOT 6 CLOSED

diff --git a/gl21-cube/cube.go b/gl21-cube/cube.go
index 5a84ebc..b26b8f2 100644
--- a/gl21-cube/cube.go
+++ b/gl21-cube/cube.go
@@ -29,6 +29,8 @@ func init() {
        runtime.LockOSThread()
 }
 
+const width, height = 1280, 720
+
 func main() {
        if err := glfw.Init(); err != nil {
                log.Fatalln("failed to initialize glfw:", err)
@@ -38,7 +40,8 @@ func main() {
        glfw.WindowHint(glfw.Resizable, glfw.False)
        glfw.WindowHint(glfw.ContextVersionMajor, 2)
        glfw.WindowHint(glfw.ContextVersionMinor, 1)
-       window, err := glfw.CreateWindow(800, 600, "Cube", nil, nil)
+       monitor := glfw.GetPrimaryMonitor()
+       window, err := glfw.CreateWindow(width, height, "Cube", monitor, nil)
        if err != nil {
                panic(err)
        }
@@ -115,7 +118,9 @@ func setupScene() {
 
        gl.MatrixMode(gl.PROJECTION)
        gl.LoadIdentity()
-       gl.Frustum(-1, 1, -1, 1, 1.0, 10.0)
+       // Correct the projection for the monitor's aspect ratio.
+       f := ((float64(width) / height) - 1) / 2
+       gl.Frustum(-1-f, 1+f, -1, 1, 1.0, 10.0)
        gl.MatrixMode(gl.MODELVIEW)
        gl.LoadIdentity()
 }