'' examples/manual/gfx/screenglproc.bas
''
'' Example extracted from the FreeBASIC Manual
'' from topic 'SCREENGLPROC'
''
'' See Also: https://www.freebasic.net/wiki/wikka.php?wakka=KeyPgScreenglproc
'' --------

'' include fbgfx.bi for some useful definitions
#include "fbgfx.bi"

Dim SwapInterval As Function(ByVal interval As Integer) As Integer
Dim extensions As String

'' Setup OpenGL and retrieve supported extensions
If ScreenRes(640, 480, 32, , FB.GFX_OPENGL) <> 0 Then
	Print "Could not set the requested OpenGL graphics mode"
	Sleep
	End 1
End If

ScreenControl FB.GET_GL_EXTENSIONS, extensions

If (InStr(extensions, "WGL_EXT_swap_control") <> 0) Then
	'' extension supported, retrieve proc address
	SwapInterval = ScreenGLProc("wglSwapIntervalEXT")
	If (SwapInterval <> 0) Then
		'' Ok, we got it. Set OpenGL to wait for vertical sync on buffer swaps
		SwapInterval(1)
	End If
End If