; UpdateNormals Example
; ---------------------

; Lighting needs normals. When you build or deform a mesh by hand its
; normals are missing or stale, so the lighting looks wrong.
; UpdateNormals recalculates every normal from the triangle shapes.
; Space crumples the ground; U repairs the lighting.

Graphics3D 640,480
SetBuffer BackBuffer()

camera=CreateCamera()
PositionEntity camera,0,3,-5
RotateEntity camera,30,0,0

light=CreateLight()
RotateEntity light,45,45,0

SeedRnd MilliSecs()

; Build a 13 x 13 grid of vertices as rocky ground
ground=CreateMesh()
surf=CreateSurface(ground)
For j=0 To 12
    For i=0 To 12
        AddVertex surf,i*0.4-2.4,Rnd(0,0.5),2.4-j*0.4
    Next
Next

; Connect each grid cell with two upward-facing triangles
For j=0 To 11
    For i=0 To 11
        v00=j*13+i
        AddTriangle surf,v00,v00+1,v00+14
        AddTriangle surf,v00,v00+14,v00+13
    Next
Next

EntityColor ground,90,200,100

; Calculate correct normals for the starting terrain
UpdateNormals ground
stale=0

While Not KeyDown(1)

    ; Space crumples the terrain - normals are now STALE, so the
    ; lighting no longer matches the new shape
    If KeyHit(57) Then
        For j=0 To 12
            For i=0 To 12
                VertexCoords surf,j*13+i,i*0.4-2.4,Rnd(0,0.5),2.4-j*0.4
            Next
        Next
        stale=1
    EndIf

    ; U recalculates the normals - the documented command
    If KeyHit(22) Then UpdateNormals ground : stale=0

    ; Arrow keys move the camera
    If KeyDown(200) Then MoveEntity camera,0,0,0.1
    If KeyDown(208) Then MoveEntity camera,0,0,-0.1
    If KeyDown(203) Then TurnEntity camera,0,1,0
    If KeyDown(205) Then TurnEntity camera,0,-1,0

    RenderWorld

    Text 0,0,"Space: crumple terrain   U: UpdateNormals   Arrow keys: move camera   Esc: exit"
    If stale Then
        Text 0,20,"Normals STALE - lighting is wrong. Press U to fix it"
    Else
        Text 0,20,"UpdateNormals applied - lighting matches the shape"
    EndIf

    Flip

Wend

End