Usage of render states in Direct3D 11.x?

Question

I know there are four different render states. They are

Blend State 
Depth Stencil State 
Rasterizer State 
Sampler State 

One of my Direct3D reference books say that Direct3D is a state machine. But how, where do we use these in game development?

Answer 1

This is quite broad.

• Blend state is used by the Output merger and you can configure it however you want to blend together outputs from a pixel shader and the render target or backbuffer.
• Depth stencil state is used if you have a depth stencil view bound to your rendertarget or backbuffer. You can configure it if you want depth or stencil test functionality.
• Rasterizer state describes the rasterizer fuctionality which occurs between primitive outputting shaders and pixel shaders and decides which pixels will be executed the pixels shader on.
• Sampler state is a texture sampler state which holds information how to sample a given texture resource.

You can usually create these by

ID3D11DeviceContext::CreateXYZState(state_description,state_pointer);

where XYZ is your 'Sampler', 'Rasterizer', etc., state_description is a D3D11_SAMPLER_DESC (or rasterizer, etc.) structure object's address which you fill in with the desired parameters. state_pointer is the address of your state which you want to create.
You can use these states by enabling them before a draw call by calling the relevant method of the device context such as ID3D11DeviceContext::RSSetState(rasterizerstate); for example.

There is much more to this topic, you should try them out one by one to understand it completely.

Answer 2

Direct3D 11 is a 'state machine' in the same way as all modern graphic APIs. The full state is much more complicated than these four objects. Here's a list of basic Direct3D 11 state (ignoring optional stuff like Geometry Shader, Stream Out, Tessellation Domain/Hull Shaders, DirectCompute Shaders/Resources, and Queries):

Input Assembler

• Input layout
• 1 or more vertex buffers
• 0 or 1 index buffer
• index buffer format (16-bit or 32-bit)
• primitive topology setting

Vertex Shader

• Vertex shader program
• up to 16 constant buffers
• up to 128 textures (shader resource view + texture resource)
• up to 16 samplers (ID3D11SamplerState)

Rasterizer

• rasterizer state (ID3D11RasterizerState)
• up to 16 viewports
• up to 16 scissor rectangles

Pixel Shader

• Pixel shader program
• up to 16 constant buffers
• up to 128 textures (shader resource view + texture resource)
• up to 16 samplers (ID3D11SamplerState)

Output Merger

• blend state (ID3D11BlendState)
• depth/stencil state (ID3D11DepthStencilState)
• up to 8 render targets (render target resource view + texture resource)

So to draw anything, you have to set all this state before you call Draw or DrawIndexed.