FIELD OF THE INVENTION

The present invention generally relates to graphics processors and, more particularly, to a graphics processor architecture employing a single shader.

BACKGROUND OF THE INVENTION

In computer graphics applications, complex shapes and structures are formed through the sampling, interconnection and rendering of more simple objects, referred to as primitives. An example of such a primitive is a triangle, or other suitable polygon. These primitives, in turn, are formed by the interconnection of individual pixels. Color and texture are then applied to the individual pixels that comprise the shape based on their location within the primitive and the primitives orientation with respect to the generated shape; thereby generating the object that is rendered to a corresponding display for subsequent viewing.

The interconnection of primitives and the application of color and textures to generated shapes are generally performed by a graphics processor. Conventional graphics processors include a series of shaders that specify how and with what corresponding attributes, a final image is drawn on a screen, or suitable display device. As illustrated in FIG. 1, a conventional shader?10?can be represented as a processing block?12?that accepts a plurality of bits of input data, such as, for example, object shape data (14) in object space (x,y,z); material properties of the object, such as color (16); texture information (18); luminance information (20); and viewing angle information (22) and provides output data (28) representing the object with texture and other appearance properties applied thereto (x′, y′, z′).

In exemplary fashion, as illustrated in FIGS. 2A-2B, the shader accepts the vertex coordinate data representing cube?30?(FIG. 2A) as inputs and provides data representing, for example, a perspectively corrected view of the cube?30′ (FIG. 2B) as an output. The corrected view may be provided, for example, by applying an appropriate transformation matrix to the data representing the initial cube?30. More specifically, the representation illustrated in FIG. 2B is provided by a vertex shader that accepts as inputs the data representing, for example, vertices V_X, V_Y?and V_Z, among others of cube?30?and providing angularly oriented vertices V_X′, V_Y′?and V_Z′, including any appearance attributes of corresponding cube?30′.

In addition to the vertex shader discussed above, a shader processing block that operates on the pixel level, referred to as a pixel shader is also used when generating an object for display. Generally, the pixel shader provides the color value associated with each pixel of a rendered object. Conventionally, both the vertex shader and pixel shader are separate components that are configured to perform only a single transformation or operation. Thus, in order to perform a position and a texture transformation of an input, at least two shading operations and hence, at least two shaders, need to be employed. Conventional graphics processors require the use of both a vertex shader and a pixel shader in order to generate an object. Because both types of shaders are required, known graphics processors are relatively large in size, with most of the real estate being taken up by the vertex and pixel shaders.

In addition to the real estate penalty associated with conventional graphics processors, there is also a corresponding performance penalty associated therewith. In conventional graphics processors, the vertex shader and the pixel shader are juxtaposed in a sequential, pipelined fashion, with the vertex shader being positioned before and operating on vertex data before the pixel shader can operate on individual pixel data.

Thus, there is a need for an improved graphics processor employing a shader that is both space efficient and computationally effective.

DETAILED DESCRIPTION OF THE INVENTION

Briefly stated, the present invention is directed to a graphics processor that employs a unified shader that is capable of performing both the vertex operations and the pixel operations in a space saving and computationally efficient manner. In an exemplary embodiment, a graphics processor according to the present invention includes an arbiter circuit for selecting one of a plurality of inputs for processing in response to a control signal; and a shader, coupled to the arbiter, operative to process the selected one of the plurality of inputs, the shader including means for performing vertex operations and pixel operations, and wherein the shader performs one of the vertex operations or pixel operations based on the selected one of the plurality of inputs.

The shader includes a general purpose register block for storing at least the plurality of selected inputs, a sequencer for storing logical and arithmetic instructions that are used to perform vertex and pixel manipulation operations and a processor capable of executing both floating point arithmetic and logical operations on the selected inputs according to the instructions maintained in the sequencer. The shader of the present invention is referred to as a "unified" shader because it is configured to perform both vertex and pixel operations. By employing the unified shader of the present invention, the associated graphics processor is more space efficient than conventional graphics processors because the unified shader takes up less real estate than the conventional multi-shader processor architecture.

In addition, according to the present invention, the unified shader is more computationally efficient because it allows the shader to be flexibly allocated to pixels or vertices based on workload.

Referring now to FIG. 3, illustrated therein is a graphics processor incorporating a conventional pipeline architecture. As shown, the graphics processor40?includes a vertex fetch block?42?which receives vertex information relating to a primitive to be rendered from an off-chip memory?55?on line?41. The fetched vertex data is then transmitted to a vertex cache?44?for storage on line?43. Upon request, the vertex data maintained in the vertex cache?44?is transmitted to a vertex shader?46?on line?45. As discussed above, an example of the information that is requested by and transmitted to the vertex shader?46?includes the object shape, material properties (e.g. color), texture information, and viewing angle. Generally, the vertex shader?46?is a programmable mechanism which applies a transformation position matrix to the input position information (obtained from the vertex cache?44), thereby providing data representing a perspectively corrected image of the object to be rendered, along with any texture or color coordinates thereof.

After performing the transformation operation, the data representing the transformed vertices are then provided to a vertex store?48?on line?47. The vertex store?48?then transmits the modified vertex information contained therein to a primitive assembly block?50?on line?49. The primitive assembly block?50?assembles, or converts, the input vertex information into a plurality of primitives to be subsequently processed. Suitable methods of assembling the input vertex information into primitives is known in the art and will not be discussed in greater detail here. The assembled primitives are then transmitted to a rasterization engine?52, which converts the previously assembled primitives into pixel data through a process referred to as walking. The resulting pixel data is then transmitted to a pixel shader?54?on line?53.

The pixel shader?54?generates the color and additional appearance attributes that are to be applied to a given pixel, and applies the appearance attributes to the respective pixels. In addition, the pixel shader?54?is capable of fetching texture data from a texture map?57?as indexed by the pixel data from the rasterization engine?52?by transmitting such information on line?55?to the texture map. The requested texture data is then transmitted back from the texture map?57?on line?57′ and stored in a texture cache?56?before being routed to the pixel shader on line?58. Once the texture data has been received, the pixel shader?54?then performs specified logical or arithmetic operations on the received texture data to generate the pixel color or other appearance attribute of interest. The generated pixel appearance attribute is then combined with a base color, as provided by the rasterization engine on line?53, to thereby provide a pixel color to the pixel corresponding at the position of interest. The pixel appearance attribute present on line?59?is then transmitted to post raster processing blocks (not shown).

As described above, the conventional graphics processor?40?requires the use of two separate shaders: a vertex shader?46?and a pixel shader?54. A drawback associated with such an architecture is that the overall footprint of the graphics processor is relatively large as the two shaders take up a large amount of real estate. Another drawback associated with conventional graphics processor architectures is that can exhibit poor computational efficiency.

Referring now to FIG. 4A, in an exemplary embodiment, the graphics processor?60?of the present invention includes a multiplexer?66?having vertex (e.g. indices) data provided at a first input thereto and interpolated pixel parameter (e.g. position) data and attribute data from a rasterization engine?74provided at a second input. A control signal generated by an arbiter?64?is transmitted to the multiplexer?66?on line?63. The arbiter?64?determines which of the two inputs to the multiplexer?66?is transmitted to a unified shader?62?for further processing. The arbitration scheme employed by the arbiter?64?is as follows: the vertex data on the first input of the multiplexer?66?is transmitted to the unified shader?62?on line?65?if there is enough resources available in the unified shader to operate on the vertex data; otherwise, the interpolated pixel parameter data present on the second input will be passed to the unified shader?62?for further processing.

Referring briefly to FIG. 5, the unified shader?62?will now be described. As illustrated, the unified shader?62?includes a general purpose register block92, a plurality of source registers: including source register A?93, source register B?95, and source register C?97, a processor (e.g. CPU)?96?and a sequencer?99. The general purpose register block?92?includes sixty four registers, or available entries, for storing the information transmitted from the multiplexer?66?on line?65?or any other information to be maintained within the unified shader. The data present in the general purpose register block?92?is transmitted to the plurality of source registers via line?109.

The processor?96?may be comprised of a dedicated piece of hardware or can be configured as part of a general purpose computing device (i.e. personal computer). In an exemplary embodiment, the processor?96?is adapted to perform 32-bit floating point arithmetic operations as well as a complete series of logical operations on corresponding operands. As shown, the processor is logically partitioned into two sections. Section?96?is configured to execute, for example, the 32-bit floating point arithmetic operations of the unified shader. The second section,?96A, is configured to perform scaler operations (e.g. log, exponent, reciprocal square root) of the unified shader.

The sequencer?99?includes constants block?91?and an instruction store?98. The constants block?91?contains, for example, the several transformation matrices used in connection with vertex manipulation operations. The instruction store?98?contains the necessary instructions that are executed by the processor?96?in order to perform the respective arithmetic and logic operations on the data maintained in the general purpose register block?92?as provided by the source registers?93-95. The instruction store?98?further includes memory fetch instructions that, when executed, causes the unified shader?62?to fetch texture and other types of data, from memory?82?(FIG. 4A). In operation, the sequencer?99?determines whether the next instruction to be executed (from the instruction store?98) is an arithmetic or logical instruction or a memory (e.g. texture fetch) instruction. If the next instruction is a memory instruction or request, the sequencer?99?sends the request to a fetch block (not shown) which retrieves the required information from memory82?(FIG. 4A). The retrieved information is then transmitted to the sequencer?99, through the vertex texture cache?68?(FIG. 4A) as described in greater detail below.

If the next instruction to be executed is an arithmetic or logical instruction, the sequencer?99?causes the appropriate operands to be transferred from the general purpose register block?92?into the appropriate source registers (93,?95,?97) for execution, and an appropriate signal is sent to the processor?96on line?101?indicating what operation or series of operations are to be executed on the several operands present in the source registers. At this point, the processor?96?executes the instructions on the operands present in the source registers and provides the result on line?85. The information present on line?85?may be transmitted back to the general purpose register block?92?for storage, or transmitted to succeeding components of the graphics processor?60.

As discussed above, the instruction store?98?maintains both vertex manipulation instructions and pixel manipulation instructions. Therefore, the unified shader?99?of the present invention is able to perform both vertex and pixel operations, as well as execute memory fetch operations. As such, the unified shader?62?of the present invention is able to perform both the vertex shading and pixel shading operations on data in the context of a graphics controller based on information passed from the multiplexer. By being adapted to perform memory fetches, the unified shader of the present invention is able to perform additional processes that conventional vertex shaders cannot perform; while at the same time, perform pixel operations.

The unified shader?62?has ability to simultaneously perform vertex manipulation operations and pixel manipulation operations at various degrees of completion by being able to freely switch between such programs or instructions, maintained in the instruction store?98, very quickly. In application, vertex data to be processed is transmitted into the general purpose register block?92?from multiplexer?66. The instruction store?98?then passes the corresponding control signals to the processor?96?on line?101?to perform such vertex operations. However, if the general purpose register block?92does not have enough available space therein to store the incoming vertex data, such information will not be transmitted as the arbitration scheme of the arbiter?64?is not satisfied. In this manner, any pixel calculation operations that are to be, or are currently being, performed by the processor?96?are continued, based on the instructions maintained in the instruction store?98, until enough registers within the general purpose register block?92?become available. Thus, through the sharing of resources within the unified shader?62, processing of image data is enhanced as there is no down time associated with the processor?96.

Referring back to FIG. 4A, the graphics processor?60?further includes a cache block?70, including a parameter cache?70A and a position cache?70B which accepts the pixel based output of the unified shader?62?on line?85?and stores the respective pixel parameter and position information in the corresponding cache. The pixel information present in the cache block?70?is then transmitted to the primitive assembly block?72?on line?71. The primitive assembly block?72?is responsible for assembling the information transmitted thereto from the cache block?70?into a series of triangles, or other suitable primitives, for further processing. The assembled primitives are then transmitted on line?73?to rasterization engine block?74, where the transmitted primitives are then converted into individual pixel data information through a walking process, or any other suitable pixel generation process. The resulting pixel data from the rasterization engine block?74?is the interpolated pixel parameter data that is transmitted to the second input of the multiplexer?66?on line?75.

In those situations when vertex data is transmitted to the unified shader?62?through the multiplexer?66, the resulting vertex data generated by the processor?96, is transmitted to a render back end block?76?which converts the resulting vertex data into at least one of several formats suitable for later display on display device?84. For example, if a stained glass appearance effect is to be applied to an image, the information corresponding to such appearance effect is associated with the appropriate position data by the render back end?76. The information from the render back end?76?is then transmitted to memory?82?and a display controller line?80?via memory controller?78. Such appropriately formatted information is then transmitted on line83?for presentation on display device?84.

Referring now to FIG. 4B, shown therein is a vertex block?61?which is used to provide the vertex information at the first input of the multiplexer?66according to an alternate embodiment of the present invention. The vertex block?61?includes a vertex fetch block?61A which is responsible for retrieving vertex information from memory?82, if requested, and transmitting that vertex information into the vertex cache?61B. The information stored in the vertex cache?61B comprises the vertex information that is coupled to the first input of multiplexer?66.

As discussed above, the graphics processor?60?of the present invention incorporates a unified shader?62?which is capable of performing both vertex manipulation operations and pixel manipulation operations based on the instructions stored in the instruction store?98. In this fashion, the graphics processor?60?of the present invention takes up less real estate than conventional graphics processors as separate vertex shaders and pixel shaders are no longer required. In addition, as the unified shader?62?is capable of alternating between performing vertex manipulation operations and pixel manipulation operations, graphics processing efficiency is enhanced as one type of data operations is not dependent upon another type of data operations. Therefore, any performance penalties experienced as a result of dependent operations in conventional graphics processors are overcome.

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