Microsoft KB Archive/152668

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HOWTO: Clear the z-buffer in Direct3D Retained Mode

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Q152668

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The information in this article applies to:


 * Microsoft DirectX 2 Software Development Kit (SDK), for Windows 95
 * Microsoft Windows 2000 Advanced Server
 * Microsoft Windows 2000 Server
 * Microsoft Windows 2000 Professional

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SUMMARY
The IDirect3DRMViewport::Clear function clears a Retained Mode viewport's z-buffer and target rendering surface. You cannot direct this function to clear the z-buffer only. If you need to clear the z-buffer without calling IDirect3DRMViewport::Clear, then you will need to extract the immediate mode viewport from the retained mode viewport and use the low level clear functions in the immediate mode API to clear the z-buffer only.

MORE INFORMATION
A set of normal Retained Mode rendering instructions may look like the following:

  scene->Move(D3DVALUE(1.0)); view->Clear; view->Render(scene); rmdev->Update; If you want to render without clearing your target surface, you will need to remove your call to Clear. If you do this, however, your z-buffer will not get cleared and your objects will not be rendered properly. If you obtain the immediate mode viewport associated with your retained mode viewport, you can clear the z-buffer without clearing the target. Call IDirect3DRMViewport::GetDirect3DViewport to retrieve the Direct3D immediate mode viewport and then call the immediate mode viewport's Clear method to clear the z-buffer. You can do this by calling IDirect3DViewport::Clear with the D3DCLEAR_ZBUFFER flag set.

Sample Code
The following code shows how you can modify your rendering calls to achieve this functionality:

LPDIRECT3DVIEWPORT d3dview;

scene->Move(D3DVALUE(1.0)); view->GetDirect3DViewport(&d3dview);

int clearflags; D3DRECT rc; clearflags = D3DCLEAR_ZBUFFER; rc.x1 = rc.y1 = 0; rc.x2 = 640; rc.y2 = 480; d3dview->Clear(1, &rc, clearflags);

view->Render(scene); rmdev->Update;