module checker_mod
use opengl_gl
use opengl_glu
use opengl_glut
implicit none

private

public :: display, myReshape, myinit
private :: makeCheckImage

integer, private, parameter :: checkImageWidth = 64
integer, private, parameter :: checkImageHeight = 64
integer(kind=GLubyte), private, &
   dimension(0:2,0:checkImageWidth-1,0:checkImageHeight-1) :: checkImage

contains

subroutine makeCheckImage()
    integer :: i, j, c
    
    do i = 0, checkImageWidth-1
       do j = 0, checkImageHeight-1
            if (iand(i,8)==0 .neqv. iand(j,8)==0) then
               c = ibset(127,7)
            else
               c = 0
            endif
            checkImage(0,i,j) = c
            checkImage(1,i,j) = c
            checkImage(2,i,j) = c
       end do
    end do
end subroutine makeCheckImage

subroutine myinit()
    call glClearColor (0.0, 0.0, 0.0, 0.0)
    call glEnable(GL_DEPTH_TEST)
    call glDepthFunc(GL_LESS)

    call makeCheckImage()
    call glPixelStorei(GL_UNPACK_ALIGNMENT, 1)
    call glTexImage2D(GL_TEXTURE_2D, 0, 3, checkImageWidth, &
       checkImageHeight, 0, GL_RGB, GL_UNSIGNED_BYTE, &
        reshape(checkImage,(/3*checkImageWidth*checkImageHeight/)))
    call glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP)
    call glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP)
    call glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR)
    call glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR)
    call glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL)
    call glEnable(GL_TEXTURE_2D)
    call glShadeModel(GL_FLAT)
end subroutine myinit

subroutine display()
    call glClear(ior(GL_COLOR_BUFFER_BIT,GL_DEPTH_BUFFER_BIT))
    call glBegin(GL_QUADS)
    call glTexCoord2f(0.0, 0.0)
    call glVertex3f(-2.0, -1.0, 0.0)
    call glTexCoord2f(0.0, 1.0)
    call glVertex3f(-2.0, 1.0, 0.0)
    call glTexCoord2f(1.0, 1.0)
    call glVertex3f(0.0, 1.0, 0.0)
    call glTexCoord2f(1.0, 0.0)
    call glVertex3f(0.0, -1.0, 0.0)

    call glTexCoord2f(0.0, 0.0)
    call glVertex3f(1.0, -1.0, 0.0)
    call glTexCoord2f(0.0, 1.0)
    call glVertex3f(1.0, 1.0, 0.0)
    call glTexCoord2f(1.0, 1.0)
    call glVertex3f(2.41421, 1.0, -1.41421)
    call glTexCoord2f(1.0, 0.0)
    call glVertex3f(2.41421, -1.0, -1.41421)
    call glEnd()
    call glutSwapBuffers()
end subroutine display

subroutine myReshape(w, h)
integer, intent(in out) :: w,h
    call glViewport(0, 0, w, h)
    call glMatrixMode(GL_PROJECTION)
    call glLoadIdentity()
    call gluPerspective(60.0_gldouble, (1.0_gldouble*w)/h, 1.0_gldouble, 30.0_gldouble)
    call glMatrixMode(GL_MODELVIEW)
    call glLoadIdentity()
    call glTranslatef(0.0, 0.0, -3.6)
end subroutine myReshape
end module checker_mod

program thismain
use checker_mod
use opengl_glut
implicit none
integer :: w
    call glutInit()
    call glutInitDisplayMode(ior(GLUT_DOUBLE,ior(GLUT_RGB,GLUT_DEPTH)))
    w = glutCreateWindow("checker")
    call myinit()
    call glutReshapeFunc (myReshape)
    call glutDisplayFunc(display)
    call glutMainLoop()
end program thismain