Explicit Register Binding in .NET framework

Encode QR Code 2d barcode in .NET framework Explicit Register Binding

We already know that the compiler will automatically assign registers to global variables. It s also possible to bind variables to a specific register.

sampler Environment; sampler SparkleNoise; float4 k_s;

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For these three global variables, the compiler will assign Environment and SparkleNoise to sampler registers, and it will assign k_s to a constant register. To force the compiler to assign to a particular register, use the register(...) syntax, as shown here:

sampler Environment : register(s1); sampler SparkleNoise : register(s0); float4 k_s : register(c12);

Now the Environment sampler will be bound to sampler register s1, SparkleNoise will be bound to sampler register s0, and k_s will be bound to constant register c12.

Annotations are metadata that can be attached to a function within angle brackets. Annotations are ignored by HLSL; they ll be covered in Part III.

The function body is all the code after the function declaration. The following function (from Tutorial 1 in 6) contains a declaration and a function body:

float4x4 WorldViewProj; float4 VertexShader_Tutorial_1(float4 inPos : POSITION) : POSITION { return mul(inPos, WorldViewProj); };

The body consists of statements that are surrounded by curly braces. The function body implements all the functionality using variables, literals, expressions, and statements. The shader body does two things: it performs a matrix multiply, and it returns a float4 result. The matrix multiply is accomplished with the mul function, which performs a 4-by-4 matrix multiply. mul is called an intrinsic function because it s already built into the HLSL library of functions. Intrinsic functions will be covered in more detail in the next section called Intrinsic Functions. The matrix multiply combines an input vector (Pos) and a composite matrix WorldViewProj. The result is that position data is transformed into projection space. This is the minimum vertex shader processing we can do. If we were using the fixed function pipeline instead of a vertex shader, the vertex data could be drawn after performing this transform.

The last statement in a function body is a return statement. Just like C, this statement returns control from the function to the statement that called the function.

Function return types can be any of the simple data types defined in the HLSL, including bool, int, half, float, and double. Return types can also be one of the complex data types such as vectors and matrices. HLSL types that refer to objects can t be used as return types, including pixelshader, vertexshader, texture, and sampler. Here s an example of a function that uses a structure for a return type:

float4x4 WorldViewProj : WORLDVIEWPROJ; struct VS_OUTPUT { float4 Pos : POSITION; }; VS_OUTPUT VS_HLL_Example(float4 inPos : POSITION) { VS_OUTPUT Out = (VS_OUTPUT)0; Out.Pos = mul(inPos, WorldViewProj); return Out; };

This shader is identical in functionality to one used in Tutorial 1 in 6. The float4 return type has been replaced with the structure VS_OUTPUT, which now contains a single float4 member.

HLSL has implemented many common graphics functions, which are called intrinsic functions, because they re built into the language. They have already been optimized, so they are likely to provide the best performance possible for the given function. Intrinsic functions cover many operations, including:

Low-level math functions such as abs, clamp, clip, max, min, and sign Higher-level math functions such as cross, det (or determinant), lerp, log, noise, pow, and sqrt Trigonometry functions such as sin, cos, tan, atan, and sinh Texture sampling functions for 2-D, 3-D, cube, and volume textures

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There are approximately 50 functions covering a wide variety of operations. The complete list of intrinsic functions is shown in Appendix C. The documentation includes the function prototype and a description of the input arguments and the function s return value. A sampling of these functions is listed in Table 7-2.