Drawing in the 3D world of a modern game WITH z-depth testing

[AkaneTendo]

(cross posting with UC)

Lately D3D games tend to abandon the fixed function pipeline and do all the transform work directly in the vertex shader. They also often do tricky things with the depth/stencil buffer as they render different parts of the scene. This can make it hard to actually draw geometry in the game world, instead of merely on top of the game world. Here's what I've come up with to get it working in one example game (bad company 2), but the strategy is generalizable.



1. Dealing with lack of fixed function pipeline usage.

Basically if the game does world/view/proj transforms in the vertex shader, you'll need to turn off the shader and set your own matrices. How you find these will be game dependent.

pDevice->GetPixelShader( &pixelshader );
pDevice->GetVertexShader( &vertexshader );

pDevice->SetPixelShader( NULL );
pDevice->SetVertexShader( NULL );

pDevice->SetTransform(D3DTS_VIEW, &view->m_viewMatrix);
pDevice->SetTransform(D3DTS_PROJECTION, &view->m_projectionMatrix);
D3DXMATRIX worldMatrix;
D3DXMatrixIdentity(&worldMatrix);
for (vector<RenderSphere>::iterator it = spheres.begin(); it != spheres.end(); it++)
{
    D3DXMatrixTranslation(&worldMatrix, it->pos.x, it->pos.y, it->pos.z);
    worldMatrix._11 = worldMatrix._22 = worldMatrix._33 = it->radius;
    pDevice->SetTransform(D3DTS_WORLD, &worldMatrix);
    sphereMesh->DrawSubset(0);
}

pDevice->SetPixelShader( pixelshader );
pDevice->SetVertexShader( vertexshader ); 

This will get you spheres drawn in the 3D world, but (sometimes) not depth testing



2. Saving the depthstencil surface
If your game renders to different depth buffers, as is often the case for weapons and hud elements depending on how they are drawn, you will need to find the depth buffer you are interested in (usually the one with game world geometry in it) and save it. What does this entail?

First, identifying the buffer. My strategy is to hook DIP and count how many calls with certain stride counts are made. Next, hook SetDepthStencilSurface. Examine the stride-call count and if enough calls were made (game-dependent), save the current surface. This is the surface you will want to set before drawing your geometry. Additionally, you may need to hook Clear, and prevent Z-buffer clears to your buffer, if the game reuses its surfaces for multiple purposes during a single frame render. If this clearing is critical to the game's functioning you may need to lock the zbuffer and copy all the bits and then restore them, but this is a significant performance hit (and is hopefully unnecessary). Alternatively you may just want to insert your own created, blank surface in lieu of allowing the game to clear the one you want.

There you go, enjoy, and please credit. Or don't, it doesn't really matter.

[haitianfeihong]

I'm glad to sit on the sofa!!!thank you for your share!!!!!!!!!!

[Macpunk]

By the way, this is one of the more creative hacks I've seen in a long time. Pretty awesome idea and quite extensible to other kinds of hacks(FOV/aim, drop cam placement marker are just a few off the top of my head).

[Xero|Hawk]

Always wanted to do that, never got around to doing it.
Great work!

[w4rlock]

By the way, this is one of the more creative hacks I've seen in a long time. Pretty awesome idea and quite extensible to other kinds of hacks(FOV/aim, drop cam placement marker are just a few off the top of my head).

Indeed , nice Work.