This means that while HLSL is a huge benefit to shader development, it does not free developers from the realities of shipping games to a target audience with graphics devices of varying capabilities. If the algorithm expressed in the HLSL shader is too complex to execute on the selected compilation target, compilation will fail. If an application is doing HLSL shader compilation at run time (as opposed to compile time or offline), the application could examine the capabilities of the Direct3D device and select the compilation target to match. One of the limitations with this entry point is a parameter that defines which of the assembly-level models (or compilation targets) the HLSL compiler should use to express the final shader code.

An application calls D3DX to compile a shader into binary assembly code with D3DXCompileShader. Of course, the ability to write an HLSL program to express a particular shading algorithm does not automatically enable it to run on any given hardware.

Application developers can work in assembly for these new models (vs_2_0, vs_3_0, ps_2_0, ps_3_0) but we expect most developers to move to HLSL for shader development. In addition to the development of the HLSL compiler, Direct3D 9 also introduced the assembly-level shader models to expose the functionality of the latest generation of graphics hardware. You can also compile shaders offline using fxc. This is nice because it means that the HLSL compiler can be updated independent of the Direct3D runtime. The runtime does not know anything about HLSL, only the binary assembly shader models. An application passes an HLSL shader to D3DX using D3DXCompileShader and gets back a binary representation of the compiled shader which in turn is passed to Microsoft Direct3D using CreatePixelShader or CreateVertexShader. For more detail, see the software development kit (SDK). The application would pass this human-readable assembly language code to the D3DX library using D3DXAssembleShader and get back a binary representation of the shader which would in turn get passed using CreateVertexShader or CreatePixelShader. Programs written to the shader models (names vs_1_1 and ps_1_1 - ps_1_4) were relatively short and were generally written by developers directly in the appropriate assembly language. For each of these virtual shader machines, an assembly language was designed. At that time, several virtual shader machines were defined, each roughly corresponding to a particular graphics processor produced by the top 3D graphics vendors. Shaders were first added to Microsoft DirectX in DirectX 8.0.

Binding a Shader Parameter to a Particular Register.

Compiling a Shader for Specific Hardware.

Que es shader model 3.0