Adjusting the Z-buffer (DX 8.1)

As I zoom out of my scene there seems to be a problem with the Z-buffer precision, see attached picture (the zig-zag lines / should be straight).

However, how can I fix this?

This should help:

VB Code:

'Check device supports hardware acceleration...
On Error Resume Next
D3D.GetDeviceCaps D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, Caps
If Err.Number = D3DERR_NOTAVAILABLE Then
    'Device type "D3DDEVTYPE_HAL" not available, ie no Hardware acceleration
    MsgBox "Hardware acceleration not supported!", vbCritical
    Initialise = False
    Exit Function
Else
    'Supports Hardware Acceleration...
    On Error GoTo ErrHandler 'Restore the error handler because we had changed it to "Resume Next" remember
    If D3D.CheckDeviceFormat(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, DispMode.Format, D3DUSAGE_DEPTHSTENCIL, D3DRTYPE_SURFACE, D3DFMT_D32) = D3D_OK Then
        'We can use a 32 bit Z-Buffer
        D3DWindow.AutoDepthStencilFormat = D3DFMT_D32
    Else
        'Could not support a 32 bit Z-Buffer, try a 24 bit Z-Buffer...
        If D3D.CheckDeviceFormat(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, DispMode.Format, D3DUSAGE_DEPTHSTENCIL, D3DRTYPE_SURFACE, D3DFMT_D24X8) = D3D_OK Then
            'We can use a 24 bit Z-Buffer
            D3DWindow.AutoDepthStencilFormat = D3DFMT_D24X8
        Else
            'Could not support a 24 bit Z-Buffer, try a 16 bit Z-Buffer...
            If D3D.CheckDeviceFormat(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, DispMode.Format, D3DUSAGE_DEPTHSTENCIL, D3DRTYPE_SURFACE, D3DFMT_D16) = D3D_OK Then
            'We can use a 16 bit Z-Buffer
            D3DWindow.AutoDepthStencilFormat = D3DFMT_D16
            Else
                MsgBox "Could not find a supported format for a Z-Buffer!", vbCritical
                Initialise = False
                Exit Function
            End If
        End If
    End If
End If

What depth of Z Buffer are you already using? This should get the biggest it can work with (hopefully ;)). I have seen this problem occurr before when I was using a 16bit one.

Thanks, but I'm already looking for the biggest possible Z-buffer which is D3DFMT_16 on my laptop.

I hoped there was a way to optimize the precision of the Z-buffer since my game world is nearly flat and I do exactly know in which distance I need a tighter Z-buffer...

Which formats are you checking? My old PC Supported D32 but my new one didn't so I had to add it to check for DM24X8 which does work on my new one. There might be another one that would work on your laptop?
I haven't heard of anything like you mentioned by changing the position of the precission before.

I'm checking those:

VB Code:

'Find best Z-buffer
    If CheckDepthBufferFormat(D3DFMT_D32) Then
        DepthBufferFormat = D3DFMT_D32
    ElseIf CheckDepthBufferFormat(D3DFMT_D24S8) Then
        DepthBufferFormat = D3DFMT_D24S8
    ElseIf CheckDepthBufferFormat(D3DFMT_D24X4S4) Then
        DepthBufferFormat = D3DFMT_D24X4S4
    ElseIf CheckDepthBufferFormat(D3DFMT_D24X8) Then
        DepthBufferFormat = D3DFMT_D24X8
    ElseIf CheckDepthBufferFormat(D3DFMT_D16) Then
        DepthBufferFormat = D3DFMT_D16
    ElseIf CheckDepthBufferFormat(D3DFMT_D15S1) Then
        DepthBufferFormat = D3DFMT_D15S1
    End If

But that's not the point. If there's no other way it's ok since the graphics card is quite old. I was just trying to optimize existing things ;)

Thanks anyways.