In particular, it includes features designed to represent data flow in stream-processing architectures such as GPUs.

Features are provided that map as directly as possible to hardware capabilities. Cg profiles must support the full ANSI C standard preprocessor capabilities: if , define , and so on. After this, the rasterizer "fills in" the triangles with fragments. Maximum array sizes may be limited by the number of available registers or other resource limits, and compilers are permitted to issue error messages in these cases. The only requirement is that char is no larger that short , short is no larger than int and long is at least as large as int The float type is as close as possible to the IEEE single precision bit floating point format. However, if the shade trees are complex, their diagrams become unwieldy. Arrays are supported, but with some limitations on size and dimensionality. Along with the required pixel processing, 3D models are composed of vertices that must be transformed properly before they are assembled into polygons, lines, and points that will be rasterized into pixels. Real-time graphics is often about balancing increased scene complexity, animation rates, and improved shading.

The function actually called at any given call site is based on the types of the arguments at that call site; the definition that best matches is called. The inspiration for the RenderMan Shading Language came from an earlier idea called shade trees. While your CPU executes a conventional application, that application also orchestrates the parallel processing of vertices and fragments on the GPU, by programs written in Cg. Because these GPUs support vertex programmability but lack true pixel programmability, this generation is transitional. Unsized arrays are dynamic typed objects that take on the size of any array assigned to them. Normalerweise erfolgt der Zugriff über Uniform-Parameter. Earlier, we told you to think of a fragment as a pixel if you did not know precisely what a fragment was. Note: If the target hardware uses a default value for this output, the compiler may choose to optimize away an explicit write specified by the user if it matches the default hardware value. However, rather than vertex attributes, the fragment processor's read-only input registers contain interpolated per-fragment parameters derived from the per-vertex parameters of the fragment's primitive.

Multiple instancing of Cg programs with CgFX is one way to address the functional variations in GPUs of different generations or different hardware vendors. There is a built-in swizzle operator:. Earlier, we told you to think of a fragment as a pixel if you did not know precisely what a fragment was. Never before have computer graphics practitioners, whether artists or programmers, had so much control over the real-time images they generate. Declarations And Declaration Specifiers. Vertex Program Profiles A few features of the Cg language that are specific to vertex program profiles are required to be implemented in the same manner for all vertex program profiles. Cg provides arrays and structures. Mandatory Computation Of Position Output Vertex program profiles may and typically do require that the program compute a position output. On the other hand, if you are not familiar with C or even programming languages in general but you enjoy computer graphics and want to learn something new, read on anyway.

Comparison operators may also be applied to bool vectors. The Cg language is powerful enough to express shading techniques that are not yet possible with all GPUs. However, the compiler is not obligated to detect such errors, even if it would be possible to do so by compile-time data-flow analysis. Minimum Requirements For If, While, For The minimum requirements are as follows: All profiles should support if , but such support is not strictly required for older hardware. The process starts with the transformation and coloring of vertices. If constant folding cannot be performed at run-time precision, it may optionally be performed using the precision indicated below for each of the numeric datatypes:. Partial support for a type requires the following:. Figure shows a shade tree for rendering a copper surface.

Never before have computer graphics practitioners, whether artists or programmers, had so much control over the real-time images they generate. However, to guarantee interoperability of one program's output with another program's input when automatic binding is performed, it is necessary to put all of the variables in a single struct. The sampler type is deprecated and only provided for backwards compatibility with Cg 1. Bestandteile sind u. The two approaches are not mutually exclusive, as is discussed later. Conditional Operator? Computer graphics hardware is advancing at incredible rates. Combining reciprocal and reciprocal square root operations with vector multiplication and dot products, respectively, enables vector-by-scalar division and vector normalization. There is a built-in swizzle operator:. Instead of supporting the conventional transformation and lighting modes specified by OpenGL and DirectX 7, these GPUs let the application specify a sequence of instructions for processing vertices.

This specification uses the word "program" to refer to the top-level function, any functions the top-level function calls, and any global variables or typedef definitions it references. Uniform non-static variables may have their value set through the run-time API. Compile-time constant folding is preferably performed at the same precision that would be used if the operation were performed at run time. On the other hand, you may find Cg is easier to learn by doing. The choice of a compilation profile is made externally to the language, by using a compiler command-line switch, for example. If a function definition does not include a profile, the function is referred to as an "open-profile" function. In addition to being specialized for graphics, Cg and other shading languages are different from conventional programming languages because they are based on a data-flow computational model. This meant that the CPU was responsible for updating all the pixels. Undaunted, computer graphics practitioners continue to rise to the challenge. These are changes within Cg that could cause a program that compiles without errors to behave in a manner different from C: The type promotion rules for constants are different when the constant is not explicitly typed using a type cast or type suffix.

Cg is just one component of the overall software and hardware infrastructure for rendering complex 3D scenes with programmable GPUs at real-time rates. All integral types are implicitly signed, there is no signed keyword. Figure shows this sequence of operations. Rasterization is the process of determining the set of pixels covered by a geometric primitive. Both operands are scalars with numeric or bool type. The output result registers are write-only. However, if the shade trees are complex, their diagrams become unwieldy. Parameters qualified as uniform are normally treated as persistent state, while varying parameters are treated as streaming data, with a new value specified for each stream record such as within a vertex array.

It is not required that all non-uniform inputs be included within a single struct in order to omit binding semantics. All semantics are profile specific so they have different meanings in different profiles , though there is some attempt to be consistent across profiles. In general, future profiles will be supersets of current profiles, so that programs written for today's profiles will compile without change using future profiles. If a program desires an output color alpha of 1. General-purpose programming languages are too open-ended for the specialized task of processing vertices and fragments. GPUs are designed to run large numbers of small threads of processing in parallel, each running a copy of the same program on a different data set. Vector conversions Vectors may be converted to scalar types selects the first element of the vector. This constant redoubling of computer power, historically known as Moore's Law, means cheaper and faster computer hardware, and is the norm for our age. For example, float2 0,1.

During the process of rendering, the renderer evaluates the shade tree associated with a given surface to determine the color of the surface in the rendered image. Namespaces Just as in C, there are two namespaces. These are changes within Cg that could cause a program that compiles without errors to behave in a manner different from C:. A packed array type is not equivalent to the same size unpacked array. In some cases, the core specification distinguishes between vertex-program and fragment-program profiles, with different minimum capabilities for each. This project fostered a new line of computer graphics research into hardware-amenable shading languages by Marc Olano and others at UNC. Profiles Compilation of a Cg program, a top-level function, always occurs in the context of a compilation profile. However, subscripting with run-time computed indices is not required to be supported. Both are required to render scenes at the interactive rates and quality standards that users of 3D applications and games demand. Fixed-point data types do not have IEEE-defined rules.

CgFX offers a format to encode complex multipass effects, including designating which Cg program is used for each rendering pass. Constant literals are defined as in C, including an optional 0 or 0x prefix for octal or hexadecimal constants, and e exponent suffix for floating point constants. Syntax For Parameters In Function Definitions Functions are declared in a manner similar to C, but the parameters in function definitions may include a binding semantic discussed later and a default value. Both operands are vectors with numeric or bool type, where the two vectors are of the same size, which is less than or equal to four. This means that CgFX can significantly improve the artistic workflow from DCC applications to real-time games and other 3D applications. As explained in Section 1. Fragment Program Profiles A few features of the Cg language that are specific to fragment program profiles are required to be implemented in the same manner for all fragment program profiles. It is not possible to declare a packed array of unpacked arrays. Additionally, if , while , and for require bool expressions in the appropriate places.

Each declaration is visible "in scope" from the point of its declarator until the end of the enclosing block or the end of the compilation unit if outside any block. Each object defined within the block will have a unique slot in the constant buffer. If a real-time shading language is such a good idea, why didn't someone invent Cg sooner? Constant literals are defined as in C, including an optional 0 or 0x prefix for octal or hexadecimal constants, and e exponent suffix for floating point constants. When declaring an array of arrays in a single declaration, the packed modifier refers to all of the arrays. Uniform non-static variables may have their value set through the run-time API. As a result, array assignments semantically perform a copy operation for the entire array. If so, they may not be compiled as a program and are not visible externally Function Overloading And Optional Arguments Cg supports function overloading; that is you may define multiple functions with the same name. Softimage XSI 3. If a function is present in the source code, but not called directly or indirectly by the top-level function, it is free to use capabilities that are not supported by the current profile.

Declarations And Declaration Specifiers. Fragment Program Profiles A few features of the Cg language that are specific to fragment program profiles are required to be implemented in the same manner for all fragment program profiles. If we declare float4x4 a , then a[3] is equivalent to a. Your Cg programs actually execute within the GPU of your computer. Softimage XSI 3. Constant buffers are used to define uniform blocks in Cg. Figure shows a shade tree for rendering a copper surface. Statements are expressed just as in C, unless an exception is stated elsewhere in this document. The CgFX file format encapsulates multiple implementations of Cg programs for a given shader.

Vector conversions Vectors may be converted to scalar types selects the first element of the vector. The term "fragment" is used because rasterization breaks up each geometric primitive, such as a triangle, into pixel-sized fragments for each pixel that the primitive covers. Statements are expressed just as in C, unless an exception is stated elsewhere in this document. Multiple instancing also lets you develop a Cg program specialized for a particular 3D API—for example, if OpenGL exposes extra functionality through an extension. Some array types may be optionally designated as packed , using the packed type modifier. Instead, graphics hardware designers build the "smarts" of pixel updates into the GPU. Real-time graphics is often about balancing increased scene complexity, animation rates, and improved shading. A function that takes no parameters may be declared in one of two ways: As in C, using the void keyword: functionName void With no parameters at all: functionName Functions may be declared as static. A vector may also be implicitly converted to another vector of the same size and compatible element type.

The varying inputs to the program come from this top-level function's varying in parameters, and any global varying variables that do not have an out modifier. This realization provided the impetus for a new kind of programming language known as a shading language. This core Cg specification requires certain minimum capabilities for all profiles. It is not required that all non-uniform inputs be included within a single struct in order to omit binding semantics. What is a fragment? Because Cg specializes in transforming vertices and fragments, it does not currently include many of the complex features required for massive software engineering tasks. The unqualified types of T1 and T2 are equivalent, and both types have the same qualifications. Profiles Compilation of a Cg program, a top-level function, always occurs in the context of a compilation profile. Vertex Program Profiles A few features of the Cg language that are specific to vertex program profiles are required to be implemented in the same manner for all vertex program profiles. This is a huge boon for 3D content developers.

The restrictions provided by a compilation profile are only needed for code generation, and are therefore only applied to those functions for which code is being generated. Function parameters with no in , out , or inout specifier are implicitly in inline Only usable on a function definition. Both operands must be vectors of the same size. Comparison operators may also be applied to numeric or bool scalars. Unsized arrays are dynamic typed objects that take on the size of any array assigned to them. Function Calls A function call returns an rvalue. The second force is the vast amount of computation required to simulate the world around us. Matrix conversions Matrixes may be converted to a scalar type selects to 0,0 element. Computer graphics hardware is advancing at incredible rates.

Implementations are required to support indexing of vectors and matrices with constant indices. Linux bit tgz tarball rpm for RedHat deb for Debian and Ubuntu. Reserved keywords goto , switch , case , and default are not supported, nor are labels. General-purpose programming languages are too open-ended for the specialized task of processing vertices and fragments. Some compilation profiles may allow some precision flexibility for the hardware; in such cases the compiler should ideally perform the constant folding at the highest hardware precision allowed for that data type in that profile. It is often helpful to have a way to bundle all the information required to render a 3D model, including its associated Cg program. The result of a shade tree evaluation at a given point on a surface is the color of that point. Vertex profiles may omit support for fixed operations, but must still support definition of fixed variables. When referenced, an object may be interpreted as having a particular type.

However, the box is not really a black box because you get to determine, by means of the Cg programs you write, exactly what happens inside. Partial support for a type requires the following: Definitions and declarations using the type are supported. DirectX 8 pixel shaders and various vendor-specific OpenGL extensions expose this generation's fragment-level configurability. Features are provided that map as directly as possible to hardware capabilities. The comparison operation is performed in elementwise fashion to produce a bool vector of the same size. However, profiles must support sizes of at least float arr[8] , float4 arr[8] , and float4x4 arr[4][4]. The RenderMan Shading Language grew out of shade trees and the realization that open-ended control of the appearance of rendered surfaces in the pursuit of photorealism requires programmability. The programmable vertex processor is the hardware unit that runs your Cg vertex programs, whereas the programmable fragment processor is the unit that runs your Cg fragment programs. The profile restrictions are only applied to the top-level function that is being compiled and to any variables or functions that it references, either directly or indirectly.

This type is meaningful only at compile time; it is not possible to declare objects of type cfloat. Objects may be declared as unsized arrays by using a declaration with an empty size [] and no initializer. Cg Toolkit Download. GPUs are designed to run large numbers of small threads of processing in parallel, each running a copy of the same program on a different data set. Each declaration is visible "in scope" from the point of its declarator until the end of the enclosing block or the end of the compilation unit if outside any block. Binding semantics are described in the Binding Semantics section. Namensräume Artikel Diskussion. The influence of these programming interfaces on Cg is ongoing, as is explained in the next section. Some compilation profiles may allow some precision flexibility for the hardware; in such cases the compiler should ideally perform the constant folding at the highest hardware precision allowed for that data type in that profile. Even though these hard-wired graphics algorithms could be configured by graphics applications in a variety of ways, the applications could not reprogram the hardware to do tasks unanticipated by the designers of the hardware.

The inspiration for the RenderMan Shading Language came from an earlier idea called shade trees. The term "fragment" is used because rasterization breaks up each geometric primitive, such as a triangle, into pixel-sized fragments for each pixel that the primitive covers. Some type conversions are allowed implicitly, while others require an cast. OpenGL is not limited to a single operating or windowing system. Marks the parameter or varying as an output from the function or program uniform Usable on global variables and parameters to the top-level main function of a program and to define constant buffers see the Constant Buffers section. This is version 3. Vertex program profiles may and typically do require that the program compute a position output. Earlier, we mentioned how Cg leverages C's syntax and semantics. The Cg compiler is not a separate program but part of a library known as the Cg runtime. Arrays with size [1] may be declared but are considered a different type from the corresponding non-array type.

Einen anderen Ansatz verfolgt Sh als Metasprache. No implicit conversions of struct types are allowed. If there is a function with a dynamically typed formal argument which is compatible with the actual parameter type, remove all functions whose corresponding parameter is not similarly compatible. Some compilation profiles may allow some precision flexibility for the hardware; in such cases the compiler should ideally perform the constant folding at the highest hardware precision allowed for that data type in that profile. Broadly, this type of language is called a shading language. The extensive low-level programming that had been required to achieve optimal performance could now be delegated to a compiler, which optimizes the code output and handles tedious instruction scheduling. No GPU can execute Cg programs directly from their textual form. Much of this chapter is background that provides valuable context for understanding Cg and using it effectively. If the constant includes a decimal point or an 'e' exponent suffix, it is implicitly typed as cfloat.

Non-static variables may have a semantic associated with them. The restrictions provided by a compilation profile are only needed for code generation, and are therefore only applied to those functions for which code is being generated. Some of the declaration specifiers are the same as those in ANSI C; others are new to Cg const Marks a variable as a constant that cannot be assigned to within the program. Minimum Requirements For If, While, For The minimum requirements are as follows: All profiles should support if , but such support is not strictly required for older hardware. For example, to create a three-vector from a scalar, use one of the following: 1. An assignment of an expression to a dynamic typed object is only possible if the type of the expression is compatible with the dynamic object type. It is often helpful to have a way to bundle all the information required to render a 3D model, including its associated Cg program. Every time a vertex is processed or the rasterizer generates a fragment while rendering a 3D scene, your corresponding vertex or fragment Cg program executes. However, rather than vertex attributes, the fragment processor's read-only input registers contain interpolated per-fragment parameters derived from the per-vertex parameters of the fragment's primitive.

See the function overloading section for the precise rules. Functions are declared in a manner similar to C, but the parameters in function definitions may include a binding semantic discussed later and a default value. To put Cg into its proper context, you need to understand how GPUs render images. It may be possible to define binding semantics on inputs and outputs by using an external API that manipulates the programs environment. For 3D scenes, the GPU typically processes every pixel on the screen many times to account for how objects occlude each other, or to improve the appearance of each pixel. The Cg language makes it possible for you to control the shape, appearance, and motion of objects drawn using programmable graphics hardware. Current Cg implementations do not provide pointers or even memory allocation though future implementations may, and keywords are appropriately reserved. We will explain many of these tasks in subsequent chapters.

Cg provides arrays and structures. Function and operator overloading is supported. Profiles may define a maximum allowable size for packed arrays, but must support at least size 4 for packed vector 1D array types, and 4x4 for packed matrix 2D array types. GPUs are designed to run large numbers of small threads of processing in parallel, each running a copy of the same program on a different data set. Next, the primitive assembly step creates triangles from the vertices, as the dotted lines indicate. The Cg runtime is a standard set of subroutines used to load, compile, manipulate, and configure Cg programs for execution by the GPU. If so, they may not be compiled as a program and are not visible externally Function Overloading And Optional Arguments Cg supports function overloading; that is you may define multiple functions with the same name. An accompanying development toolkit is provided for using and parsing CgFX files. Open-profile functions apply to all profiles.

T1 and T2 are arrays of equivalent types with the same number of elements. Reality is just too real. Fragment profiles must support the fixed type, but may implement it with the same precision as the half or float types. Some implicit conversions may cause a warning, which can be suppressed by using an explicit cast. Exponential, logarithmic, and trigonometric approximations facilitate lighting, fog, and geometric computations. When declaring an array of arrays in a single declaration, the packed modifier refers to all of the arrays. Add all visible functions with a matching name in the calling scope to the set of function candidates. Fortunately, this situation has changed.

We call this static compilation. Many operators support per-element vector operations. Next, the primitive assembly step creates triangles from the vertices, as the dotted lines indicate. Each profile must have a separate specification that describes its characteristics and limitations. Think of a Cg program as a black box into which vertices or fragments flow on one side, are somehow transformed, and then flow out on the other side. These types are used by the compiler for constant type conversions. The specifiers uniform and varying specify how data is transferred between the rest of the world and a Cg program. Your program not only must be correct, but it also must limit itself to the restrictions imposed by the particular profile used to compile your Cg program.

Note that conversions happen prior to performing the operation. Global variables are declared and used as in C. Arrays are supported, but with some limitations on size and dimensionality. T1 and T2 are functions with equivalent return types, the same number of parameters, and all corresponding parameters are pair-wise equivalent. The core Cg language specification is sufficiently complete to allow all of these functions to be parsed. Another method available for specifying a semantic for an output value is to return a struct , and to specify the binding semantic s with elements of the struct when the struct is defined. Broadly, this type of language is called a shading language. Figure The Programmable Graphics Pipeline. By and large, these restrictions are not permanent limitations in the language, but rather are indicative of the capabilities of today's highest performance GPUs. The Cg compiler first translates your Cg program into a form accepted by the application's choice of 3D programming interface, either OpenGL or Direct3D.

No implicit conversions of struct types are allowed. Figure Inspirations for Cg's Development. Cg is a language for both current and future GPUs. Each declarator in a declaration may optionally have a semantic specified with it. Partial Support Of Types This specification mandates "partial support" for some types. Unlike C, side effects in the expressions in the second and third operands are always executed, regardless of the condition. Download the Cg 3. If a type is defined using a typedef that has the same name as a profile, the identifier is treated as a type name, and is not available for profile overloading at any subsequent point in the file. Function and operator overloading is supported.

It marries programmatic control of these attributes with the incredible speed and capabilities of today's graphics processors. Cg is just one component of the overall software and hardware infrastructure for rendering complex 3D scenes with programmable GPUs at real-time rates. Trailing arguments with initializers are optional arguments; defining a function with optional arguments is equivalent to defining multiple overloaded functions that differ by having and not having the optional argument. This "position invariance" is particularly important for multipass rendering. If a candidate function has excess formal parameters, and each of the excess parameters has a default value, do not eliminate the function. This is version 3. A warning may be issued if the conversion is implicit and it is possible that precision is lost. Answer this: Where do vertex and fragment programs fit into the pipeline?

When declaring an array of arrays in a single declaration, the packed modifier refers to all of the arrays. You may be surprised to learn that the GPU now exceeds the CPU in the number of transistors present in each microchip. There is a built-in swizzle operator:. This constant redoubling of computer power, historically known as Moore's Law, means cheaper and faster computer hardware, and is the norm for our age. First, Cg bases its syntax and semantics on the general-purpose C programming language. For each actual parameter expression in sequence left to right , perform the following: a. However, to guarantee interoperability of one program's output with another program's input when automatic binding is performed, it is necessary to put all of the variables in a single struct. These operations include add, multiply, multiply-add, dot product, minimum, and maximum. The unsigned type is preferably a bit ordinal value. There are several changes that force the same operation to be expressed differently in Cg than in C:.

These two programmable processors in your GPU require you, the application programmer, to supply a program for each processor to execute. There is a similar built-in swizzle operator for matrices:. An accompanying development toolkit is provided for using and parsing CgFX files. The only requirement is that char is no larger that short , short is no larger than int and long is at least as large as int The float type is as close as possible to the IEEE single precision bit floating point format. The function actually called at any given call site is based on the types of the arguments at that call site; the definition that best matches is called. While your CPU executes a conventional application, that application also orchestrates the parallel processing of vertices and fragments on the GPU, by programs written in Cg. Vertex Program Profiles A few features of the Cg language that are specific to vertex program profiles are required to be implemented in the same manner for all vertex program profiles. Cg was developed based on the ANSI-C language with the following major additions, deletions, and changes. These tests involve the fragment's final color or depth, the pixel location, and per-pixel values such as the depth value and stencil value of the pixel. Finally, a frame buffer write operation replaces the pixel's color with the blended color.

Definition A declaration that also causes storage to be reserved for an object or code that will be generated for a function named by an identifier is a definition. T1 and T2 are functions with equivalent return types, the same number of parameters, and all corresponding parameters are pair-wise equivalent. Our eyes consume and our brains comprehend images of our 3D world at an astounding rate and with startling acuity. T1 and T2 are arrays of equivalent types with the same number of elements. See the function overloading section for the precise rules. Syntax For Parameters In Function Definitions Functions are declared in a manner similar to C, but the parameters in function definitions may include a binding semantic discussed later and a default value. For example, Cg programs can perform physical simulation, compositing, and other nonshading tasks. Multiple instancing also lets you develop a Cg program specialized for a particular 3D API—for example, if OpenGL exposes extra functionality through an extension. Sizes of vectors and matrices must be appropriately matched, according to standard mathematical rules. Both operands are scalars with numeric or bool type.

If a function is present in the source code, but not called directly or indirectly by the top-level function, it is free to use capabilities that are not supported by the current profile. Applications using Cg then call Cg runtime routines, all prefixed with the letters cg , to compile and manipulate Cg programs. Global variables are declared and used as in C. Cg enables a specialized style of parallel processing. However, the box is not really a black box because you get to determine, by means of the Cg programs you write, exactly what happens inside. Because Cg specializes in transforming vertices and fragments, it does not currently include many of the complex features required for massive software engineering tasks. This realization provided the impetus for a new kind of programming language known as a shading language. Mandatory Computation Of Position Output Vertex program profiles may and typically do require that the program compute a position output. Fragment profiles are not required to support any operations on arbitrarily sized arrays; only support for vectors and matrices is required.

We are unlikely ever to reach a point where computer graphics becomes a substitute for reality. Cg also provides an abstract execution model that matches the GPU's execution model. Fragment profiles are required to provide partial support as defined below for the samplerRECT data type and may optionally provide full support for this data type. Vertex profiles are required to provide partial support for the six sampler data types and may optionally provide full support for these data types. The choice of a compilation profile is made externally to the language, by using a compiler command-line switch, for example. Unlike C, side effects in the expressions in the second and third operands are always executed, regardless of the condition. For compatibility with C, integer hexadecimal constants may be specified by prefixing the constant with 0x , and integer octal constants may be specified by prefixing the constant with 0. Die Entwicklung einer Shader-Hochsprache wurde dadurch motiviert, dass das Programmieren von Vertex- und Pixel-Shadern in Maschinensprache recht kompliziert und schnell unübersichtlich ist. Figure Visualizing the Graphics Pipeline.

Fragment profiles must support the fixed type, but may implement it with the same precision as the half or float types. The toolkit exposes user-interface hooks to host applications, so that CgFX-aware applications can automatically supply meaningful controls and semantics to users and developers alike. Our third force is the sustained desire we all have to be stimulated and entertained visually. Component-wise write masking controls the output of all instructions. In a sense, everything about vertex and fragment processing back then was completely programmable. If a program desires an output color alpha of 1. Doing justice to all these contributions in the context of this tutorial is not always practical. For any supported numeric data type TYPE , implementations must support the following packed array types, which are called matrix types.

Position Invariance In many graphics APIs, the user can choose between two different approaches to specifying per-vertex computations: use a built-in configurable "fixed-function" pipeline or specify a user-written vertex program. These GPUs provide both vertex-level and pixel-level programmability. Such defaults are not exposed in the language. As explained in Section 1. Constant literals are defined as in C, including an optional 0 or 0x prefix for octal or hexadecimal constants, and e exponent suffix for floating point constants. Add all visible functions with a matching name in the calling scope to the set of function candidates. If we declare float4x4 a , then a[3] is equivalent to a. Using CgFX, artists can view and tweak Cg shaders and associated 3D content to see, from within the DCC tool of their choice, how their work will appear in a 3D game or application. Although the set of math operations for combining textures and coloring pixels expanded in this generation to include cube map textures and signed math operations, the possibilities are still limited.

Figure Visualizing the Graphics Pipeline. These operations include add, multiply, multiply-add, dot product, minimum, and maximum. A constant buffer is defined using the uniform keyword:. Instead of supporting the conventional transformation and lighting modes specified by OpenGL and DirectX 7, these GPUs let the application specify a sequence of instructions for processing vertices. Partial Support Of Types This specification mandates "partial support" for some types. These optional language features include certain control constructs and standard library functions. If there is a valid implicit cast that converts the type of the actual parameter to the unqualified type of the formal parameter of any function, remove all functions for which this is not true from the set e. The uniform qualifier simply provides information about how the initial value of the variable is to be specified and stored, through a mechanism external to the language.

Because Cg specializes in transforming vertices and fragments, it does not currently include many of the complex features required for massive software engineering tasks. Graphics hardware design has advanced, and vertex and fragment processing units in recent GPUs are truly programmable. If we declare float4x4 a , then a[3] is equivalent to a. Figure is a small portion of a complex assembly language fragment program used to represent skin. In contrast, the Cg language is fully dedicated to this task. In some cases, the core specification distinguishes between vertex-program and fragment-program profiles, with different minimum capabilities for each. Cg builds on a host of concepts in computer language design, computer hardware design, and computer graphics. If so, they may not be compiled as a program and are not visible externally Function Overloading And Optional Arguments Cg supports function overloading; that is you may define multiple functions with the same name.

Specialized instructions can make lighting and attenuation functions easier to compute. For example, you can write a Cg program to make a surface appear bumpy or to animate a virtual character. Some type conversions are allowed implicitly, while others require an cast. The specifiers uniform and varying specify how data is transferred between the rest of the world and a Cg program. As discussed earlier, when a binding semantic is applied to an output, the type of the output variable is not required to match the type of the binding semantic. At this point, however, the distinction between a fragment and a pixel becomes important. Aliasing Of Semantics Semantics must honor a copy-on-input and copy-on-output model. Matrix conversions Matrixes may be converted to a scalar type selects to 0,0 element. Cg is just one component of the overall software and hardware infrastructure for rendering complex 3D scenes with programmable GPUs at real-time rates.

Vertex profiles may choose to omit support for discard. Arrays may be designated as packed. This situation may sound limiting, but in practice the Cg programs shown in this book work on tens of millions of GPUs and produce compelling rendering effects. Comparison operators may also be applied to numeric or bool scalars. Much of this chapter is background that provides valuable context for understanding Cg and using it effectively. In addition, if the output is a formal parameter, then the binding semantic may be specified using the same approach used to specify binding semantics for inputs. This rule is applied recursively to evaluate the shade tree fully. Cg is an auxiliary language, designed specifically for GPUs. When a swizzle is used to extract a single component from a matrix, the result is a scalar. If there is at least one function with a profile that exactly matches the compilation profile, discard all functions that don't exactly match.

Skip to main content. Your compiler compiles the program into an executable that runs directly on the CPU. Some type conversions are allowed implicitly, while others require an cast. Cg differs from C in situations where either Cg's specialization for GPUs or performance justifies a change. An assignment expression has the value of the left operand after the assignment but is not an lvalue. The half type is lower-precision IEEE-like floating point. If both operands are integral the smaller type is converted to the larger type If one operand is signed integral while the other is unsigned integral and they are the same size, the signed type is converted to unsigned. This type is meaningful only at compile time; it is not possible to declare objects of type cint. For vertex profiles, it is additionally designed to support arrays of light state indexed by light number passed as uniform parameters, and arrays of skinning matrices passed as uniform parameters.

If the user wishes to mix these two approaches, it is sometimes desirable to guarantee that the position computed by the first approach is bit-identical to the position computed by the second approach. This project fostered a new line of computer graphics research into hardware-amenable shading languages by Marc Olano and others at UNC. Minimum Requirements For If, While, For The minimum requirements are as follows: All profiles should support if , but such support is not strictly required for older hardware. The choice of a compilation profile is made externally to the language, by using a compiler command-line switch, for example. Trailing arguments with initializers are optional arguments; defining a function with optional arguments is equivalent to defining multiple overloaded functions that differ by having and not having the optional argument. But for now Cg programmers will need to limit programs to ensure that they can compile and execute on existing GPUs. If a function definition does not include a profile, the function is referred to as an "open-profile" function. Finally, a frame buffer write operation replaces the pixel's color with the blended color. For example, vertex programs normally compute a position that is fed to the rasterizer, and this position is stored in an output with the binding semantic POSITION. GPUs must process so many fragments at once that arbitrary branching is not available in current GPU generations, but this is likely to change over time as hardware evolves.

A constant may be explicitly typed or implicitly typed. Semantically, this default value is copied to the output at the beginning of the execution of the fragment program. Figure Visualizing the Graphics Pipeline. In many graphics APIs, the user can choose between two different approaches to specifying per-vertex computations: use a built-in configurable "fixed-function" pipeline or specify a user-written vertex program. However, subscripting with run-time computed indices is not required to be supported. For any profile, there are two namespaces for predefined binding semantics--the namespace used for in variables and the namespace used for out variables. The name of this binding semantic is currently profile-specific -- for OpenGL profiles, the semantic state. Cg was developed based on the ANSI-C language with the following major additions, deletions, and changes. Some compilation profiles may allow some precision flexibility for the hardware; in such cases the compiler should ideally perform the constant folding at the highest hardware precision allowed for that data type in that profile. Cg programs execute in relative isolation.

For compatibility with DirectX 8 notation, there is a second form of matrix swizzle, which is described later. For example, Cg programs can perform physical simulation, compositing, and other nonshading tasks. Vertex transformation performs a sequence of math operations on each vertex. For example, the following is allowed:. It is often helpful to have a way to bundle all the information required to render a 3D model, including its associated Cg program. Semantically, this default value is copied to the output at the beginning of the execution of the fragment program. Bestandteile sind u. Before Cg existed, addressing the programmable capabilities of the GPU was possible only through low-level assembly language. CPUs are, by design, general purpose. Ein weiterer Aspekt ist die Möglichkeit zum Kompilieren für verschiedene Profile.

Marks the parameter or varying as both an input to and an output from the function or program static Only usable on global variables. This language specification describes version 3. Vertex profiles are required to support half and float , but may choose to implement half at float precision. Unfortunately, PixelFlow was too expensive and failed commercially. Some of the declaration specifiers are the same as those in ANSI C; others are new to Cg const Marks a variable as a constant that cannot be assigned to within the program. This process is known as culling. Some type conversions are allowed implicitly, while others require an cast. The term pixel is short for "picture element. Vertex profiles may choose to omit support for discard. This constant redoubling of computer power, historically known as Moore's Law, means cheaper and faster computer hardware, and is the norm for our age.

Comparison operators may also be applied to numeric or bool scalars. On the other hand, you may find Cg is easier to learn by doing. The term "fragment" is used because rasterization breaks up each geometric primitive, such as a triangle, into pixel-sized fragments for each pixel that the primitive covers. Cg uses the same operator precedence as C for operators that are common between the two languages. The resulting value is then assigned to the object or value. It has all the flow-control constructs of a modern language: loops, conditionals, and function calls. Scalar types may be implicitly converted to vectors and matrixes of compatible type. Struct types may inherit from a single interface type, and must define an implementation member function for every member function declared in the interface type.