United States Patent [19J
`Alcorn et al.
`
`[54] SYSTEM FOR MANAGING TEXTURE
`MAPPING DATA IN A COMPUTER
`GRAPHICS SYSTEM
`
`[75]
`
`Inventors: Byron A. Alcorn; Dare) N. Emmot,
`both of Fort Collins, Colo.
`
`[73] Assignee: Hewlett-Packard Company, Palo Alto,
`Calif.
`
`[21] Appl. No.: 920,334
`
`[22] Filed:
`
`Aug. 27, 1997
`
`Related U.S. Application Data
`
`[63] Continuation of Ser. No. 469,051, Jun. 6, 1995, abandoned.
`Int. Cl.6
`..................................................... G06T 15/00
`[51]
`[52] U.S. Cl. .......................... 345/430; 345/501; 345/506;
`345/507
`[58] Field of Search ..................................... 345/419, 420,
`345/429, 430, 501, 506-8
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,097,427
`5,222,205
`5,255,360
`5,276,798
`5,461,712
`5,495,563
`5,544,292
`5,548,709
`5,550,961
`5,553,208
`5,561,745
`5,572,636
`
`3/1992 Lathrop et al. ......................... 395/130
`6/1993 Larson et al. ........................... 395/130
`10/1993 Peaslee et al. .......................... 395/162
`1/1994 Peaslee et al. .......................... 395/162
`10/1995 Chelstowski et al. .. ... ... .... ... ... 395 /164
`2/1996 Winser .................................... 395/130
`8/1996 Winser .................................... 395/130
`8/1996 Hannah et al.
`... ... ... ... .... ... ... ... 395 /164
`8/1996 Chimoto ................................. 395/133
`9/1996 Murata et al. .......................... 395/125
`11/1996 Jackson et al. ......................... 395/119
`11/1996 Sakuraba et al. ....................... 395/130
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll 111111111111111111111111111111111
`US005886706A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,886,706
`Mar. 23, 1999
`
`OTHER PUBLICATIONS
`Akeley, "Reality Engine Grapahics", ACM, Computer
`Graphics Proceedings, Annual Conference Series, 1993.
`Glemot, et al, "The Image Chip for High Performance 3D
`Rendering", IEEE Computer Graphics And Applications,
`Nov. 1992.
`Primary Examiner-Rudolph J. Buchel, Jr.
`[57]
`ABSTRACT
`
`A method and apparatus for managing texture mapping data
`in a computer graphics system, the computer graphics sys(cid:173)
`tem including a host computer, primitive rendering hardware
`and a primitive data path extending between the host com(cid:173)
`puter and the primitive rendering hardware. The host com(cid:173)
`puter passes primitives to be rendered by the system to the
`primitive rendering hardware over the primitive data path.
`The host computer has a main memory that stores texture
`mapping data corresponding to the primitives to be ren(cid:173)
`dered. The primitive rendering hardware includes a local
`texture memory that locally stores the texture mapping data
`corresponding to at least one of the primitives to be ren(cid:173)
`dered. When a primitive passed to the primitive rendering
`hardware is to be rendered, a determination is made as to
`whether its corresponding texture mapping data is in the
`local texture memory. When the texture mapping data cor(cid:173)
`responding to the primitive to be rendered is in the local
`texture memory, the primitive is rendered using its corre(cid:173)
`sponding texture mapping data from the local texture
`memory. When the texture mapping data corresponding to
`the primitive to be rendered is not in the local texture
`memory, the texture mapping data corresponding to the
`primitive to be rendered is downloaded from the host
`computer main memory to the primitive rendering hardware,
`and the primitive is rendered using its corresponding texture
`mapping data downloaded from the main memory. The local
`texture memory may be implemented as a cache.
`
`43 Claims, 25 Drawing Sheets
`
`BUS FR0/'1 2-D CHIP
`
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`END
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`
`86
`
`Petitioner Apple Inc. - Exhibit 1005, p. 1
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 23, 1999
`Mar. 23, 1999
`
`Sheet 1 0f 25
`Sheet 1 of 25
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`5,886,706
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`Petitioner Apple Inc. - Exhibit 1005, p. 2
`
`Petitioner Apple Inc. - Exhibit 1005, p. 2
`
`

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`Petitioner Apple Inc. - Exhibit 1005, p. 3
`
`

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`Petitioner Apple Inc. - Exhibit 1005, p. 4
`
`

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`
`Petitioner Apple Inc. - Exhibit 1005, p. 5
`
`

`

`U.S. Patent
`
`Mar. 23, 1999
`
`Sheet 5 of 25
`
`5,886,706
`
`TEXEL PARAMETER OUTPUT
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`Petitioner Apple Inc. - Exhibit 1005, p. 6
`
`

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`Petitioner Apple Inc. - Exhibit 1005, p. 7
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 23, 1999
`Mar. 23, 1999
`
`Sheet 7 0f 25
`Sheet 7 of 25
`
`5,886,706
`5,886,706
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`etitioner Apple Inc. - Exhibit 1005, p. 8
`
`Petitioner Apple Inc. - Exhibit 1005, p. 8
`
`

`

`U.S. Patent
`
`Mar. 23, 1999
`
`Sheet 8 of 25
`
`5,886,706
`
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`
`Petitioner Apple Inc. - Exhibit 1005, p. 9
`
`

`

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`Petitioner Apple Inc. - Exhibit 1005, p. 10
`
`

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`Petitioner Apple Inc. - Exhibit 1005, p. 11
`
`

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`Petitioner Apple Inc. - Exhibit 1005, p. 12
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 23, 1999
`Mar. 23, 1999
`
`Sheet 12 0f 25
`Sheet 12 of 25
`
`5,886,706
`5,886,706
`
`TE}? 1
`
`ADDRESS
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`
`Petitioner Apple Inc. - Exhibit 1005, p. 13
`
`Petitioner Apple Inc. - Exhibit 1005, p. 13
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 23, 1999
`Mar. 23, 1999
`
`Sheet 13 of 25
`Sheet 13 0f 25
`
`5,886,706
`5,886,706
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`Petitioner Apple Inc. - Exhibit 1005, p. 14
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`Petitioner Apple Inc. - Exhibit 1005, p. 14
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 23, 1999
`M
`3,
`
`0
`Sheet 14 of 25
`
`5,886,706
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`Petitioner Apple Inc. - Exhibit 1005, p. 15
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`Petitioner Apple Inc. - Exhibit 1005, p. 15
`
`
`
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 23, 1999
`Mar. 23, 1999
`
`Sheet 15 of 25
`Sheet 15 0f 25
`
`5,886,706
`5,886,706
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`3at
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`Petitioner Apple Inc. - Exhibit 1005, p. 16
`
`Petitioner Apple Inc. - Exhibit 1005, p. 16
`
`

`

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`Petitioner Apple Inc. - Exhibit 1005, p. 17
`
`

`

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`BLOCK TAG {2Z·O}=fTEXTURE ID {7:01 MAP BIT, T {14:8],S{14:8]J
`
`Petitioner Apple Inc. - Exhibit 1005, p. 18
`
`

`

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`
`END
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`278
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`T{7:6]=5TID T !1.-0l
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`T{1·6]=5TID T {1.·0]
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`
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`
`T{7]=STID Tf 1]
`
`END
`:I
`
`276
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`
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`
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`t1AP117: 5{7]=0
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`
`252
`
`INTERP 5[7:0], T[7:0]
`
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`
`2TARTtJ c250
`
`Petitioner Apple Inc. - Exhibit 1005, p. 19
`
`

`

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`
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`
`306
`
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`
`YES
`
`NO
`
`ASSERT BLOCKS_TO_USE
`
`~TART) 300
`
`Petitioner Apple Inc. - Exhibit 1005, p. 20
`
`

`

`U.S. Patent
`
`Mar. 23, 1999
`
`Sheet 20 of 25
`
`5,886,706
`
`31:9
`8
`UNUSED HALT
`
`7
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`FIG 19
`
`384 _./
`
`Petitioner Apple Inc. - Exhibit 1005, p. 21
`
`

`

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`418
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`FIG 20
`
`414
`
`I WRITE TEXEL DATA I
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`
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`
`WRITE TEXEL DA TA
`
`424
`
`RD LOKI 0, tHAL T
`WRITE TEXEL_ CMD
`
`400
`
`START
`
`Petitioner Apple Inc. - Exhibit 1005, p. 22
`
`

`

`.....::. = 0--,
`
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`LR TAG
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`FIG 21
`
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`UL TA
`
`50. 7
`
`Petitioner Apple Inc. - Exhibit 1005, p. 23
`
`

`

`U.S. Patent
`US. Patent
`
`Mar. 23, 1999
`Mar. 23, 1999
`
`Sheet 23 0f 25
`Sheet 23 of 25
`
`5,886,706
`5,886,706
`
`(
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`
`Petitioner Apple Inc. - Exhibit 1005, p. 24
`
`Petitioner Apple Inc. - Exhibit 1005, p. 24
`
`

`

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`
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`
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`
`Petitioner Apple Inc. - Exhibit 1005, p. 25
`
`

`

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`Petitioner Apple Inc. - Exhibit 1005, p. 26
`
`

`

`5,886,706
`
`1
`SYSTEM FOR MANAGING TEXTURE
`MAPPING DATA IN A COMPUTER
`GRAPHICS SYSTEM
`
`CROSS-REFERENCE TO RELATED
`APPLICATION(S)
`
`This is a continuation of application Ser. No. 08/469,051
`filed on Jun. 6, 1995, now abandoned.
`
`FIELD OF THE INVENTION
`
`The present invention relates generally to a texture map(cid:173)
`ping computer graphics system and, more particularly, to a
`cache memory system for storing texture mapping data.
`
`BACKGROUND OF THE INVENTION
`
`Computer graphics systems commonly are used for dis(cid:173)
`playing graphical representations of objects on a two dimen(cid:173)
`sional display screen. Current computer graphics systems
`can provide highly detailed representations and are used in
`a variety of applications.
`In typical computer graphics systems, an object to be
`represented on the display screen is broken down into a
`plurality of graphics primitives. Primitives are basic com(cid:173)
`ponents of a graphics picture and may include points, lines, 25
`vectors and polygons, such as triangles. Typically, a
`hardware/software scheme is implemented to render, or
`draw, on the two-dimensional display screen, the graphics
`primitives that represent the view of one or more objects
`being represented on the screen.
`Typically, the primitives that define the three-dimensional
`object to be rendered are provided from a host computer,
`which defines each primitive in terms of primitive data. For
`example, when the primitive is a triangle, the host computer
`may define the primitive in terms of the x,y,z coordinates of
`its vertices, as well as the R,G,B color values of each vertex.
`Rendering hardware interpolates the primitive data to com(cid:173)
`pute the display screen pixels that are turned on to represent
`each primitive, and the R,G,B values for each pixel.
`Early graphics systems failed to display images in a
`sufficiently realistic manner to represent or model complex
`three-dimensional objects. The images displayed by such
`systems exhibited extremely smooth surfaces absent
`textures, bumps, scratches, shadows and other surface 45
`details present in the object being modeled.
`As a result, methods were developed to display images
`with improved surface detail. Texture mapping is one such
`method that involves mapping a source image, referred to as
`a texture, onto a surface of a three-dimensional object, and 50
`thereafter mapping the textured three-dimensional object to
`the two-dimensional graphics display screen to display the
`resulting image. Surface detail attributes commonly texture
`mapped include color, specular reflection, vector
`perturbation, specularity, transparency, shadows, surface
`irregularities and grading.
`Texture mapping involves applying one or more point
`elements ( texels) of a texture to each point element (pixel)
`of the displayed portion of the object to which the texture is
`being mapped. Texture mapping hardware is conventionally
`provided with information indicating the manner in which
`the texels in a texture map correspond to the pixels on the
`display screen that represent the object. Each texel in a
`texture map is defined by S and T coordinates which identify
`its location in the two-dimensional texture map. For each 65
`pixel, the corresponding texel or texels that map to it are
`accessed from the texture map, and incorporated into the
`
`30
`
`2
`final R,G,B values generated for the pixel to represent the
`textured object on the display screen.
`It should be understood that each pixel in an object
`primitive may not map in one-to-one correspondence with a
`5 single texel in the texture map for every view of the object.
`For example, the closer the object is to the view port
`represented on the display screen, the larger the object will
`appear. As the object appears larger on the display screen,
`the representation of the texture becomes more detailed.
`10 Thus, when the object consumes a fairly large portion of the
`display screen, a large number of pixels is used to represent
`the object on the display screen, and each pixel that repre(cid:173)
`sents the object may map in one-to-one correspondence with
`a single texel in the texture map, or a single texel may map
`15 to multiple pixels. However, when the object takes up a
`relatively small portion of the display screen, a much smaller
`number of pixels is used to represent the object, resulting in
`the texture being represented with less detail, so that each
`pixel may map to multiple texels. Each pixel may also map
`20 to multiple texels when a texture is mapped to a small
`portion of an object. Resultant texel data is calculated for
`each pixel that maps to more than one texel, and typically
`represents an average of the texels that map to that pixel.
`Texture mapping hardware systems typically include a
`local memory that stores data representing a texture asso(cid:173)
`ciated with the object being rendered. As discussed above, a
`pixel may map to multiple texels. If it were necessary for the
`texture mapping hardware to read a large number of texels
`that map to a pixel from the local memory to generate an
`average value, then a large number of memory reads and the
`averaging of many texel values would be required, which
`would be time consuming and would degrade system per(cid:173)
`formance.
`To overcome this problem, a scheme has been developed
`that involves the creation of a series of MIP (multum in
`parvo-many things in a small place) maps for each texture,
`and storing the MIP maps of the texture associated with the
`object being rendered in the local memory of the texture
`40 mapping hardware. A MIP map for a texture includes a base
`map that corresponds directly to the texture map, as well as
`a series of filtered maps, wherein each successive map is
`reduced in size by a factor of two in each of the two texture
`map dimensions. An illustrative example of a set of MIP
`maps is shown in FIG. 1. The MIP (multum in parvo-many
`things in a small place) maps include a base map 100 that is
`eight-by-eight texels in size, as well as a series of maps 102,
`104 and 108 that are respectively four-by-four texels, two(cid:173)
`by-two texels, and one texel in size.
`The four-by-four map 102 is generated by box filtering
`(decimating) the base map 100, such that each texel in the
`map 102 corresponds to an average of four texels in the base
`map 100. For example, the texel 110 in map 102 equals the
`average of the texels 112-115 in map 100, and texels 118 and
`55 120 in map 102 respectively equal the averages of texels
`121-124and125-128 in map 100. The two-by-two map 104
`is similarly generated by box filtering map 102, such that
`texel 130 in map 104 equals the average of texels 110 and
`118-120 in map 102. The single texel in map 108 is
`60 generated by averaging the four texels in map 104.
`Conventional graphics systems generally download, from
`the main memory of the host computer to the local memory
`of the texture mapping hardware, the complete series of MIP
`maps for any texture that is to be used with the primitives to
`be rendered on the display screen. Thus, the texture mapping
`hardware can access texture data from any of the series of
`MIP maps. The determination of which map to access to
`
`35
`
`Petitioner Apple Inc. - Exhibit 1005, p. 27
`
`

`

`5,886,706
`
`3
`provide the texel data for any particular pixel is based upon
`the number of texels to which the pixel maps. For example,
`if the pixel maps in one-to-one correspondence with a single
`texel in the texture map, then the base map 100 is accessed.
`However, if the pixel maps to four, sixteen or sixty-four 5
`texels, then the maps 102, 104 and 108 are respectively
`accessed because those maps respectively store texel data
`representing an average of four, sixteen and sixty-four texels
`in the texture map.
`A pixel may not map directly to any one texel in the
`selected map, and may fall between two or more texels.
`Some graphics systems employ bi-linear interpolation to
`accurately produce texel data when this occurs. If a pixel
`maps into a MIP map between two or more texel entries,
`then the resulting texel data used is a weighted average of
`the closest texel entries. Thus, the texel data corresponding
`to any pixel can be the weighted average of as many as four
`texel entries in a single map. For example, if a pixel maps
`to a location in map 102 indicated at 132, the resulting texel
`data mapping to that pixel would be the weighted average of
`the texels 110 and 118-120.
`Pixels may also not map directly into any one of the maps
`in the series of MIP maps, and may fall between two maps.
`For example, a pixel may map to a number of texels in the
`texture map that is greater than one but less than four. Some
`graphics systems address this situation by interpolating
`between the two closest MIP maps to achieve the resultant
`texel data. For the example above wherein a pixel maps to
`greater than one but less than four texels in the texture map,
`the texel data provided by maps 100 and 102 would be 30
`interpolated to achieve the resultant texel data for the pixel.
`When combined with the above-described interpolation of
`multiple texel entries in a single map, this scheme is known
`as tri-linear interpolation, and can lead to resultant texel data
`for any one pixel being generated as a weighted average of 35
`as many as eight texels, i.e., the four closest texels in each
`of the two closest maps.
`As discussed above, conventional texture mapping sys(cid:173)
`tems download the entire series of MIP maps for any texture
`associated with primitives to be rendered by the system,
`even if some of the MIP maps will not be accessed. The
`downloading of MIP maps that will not be accessed, as well
`as portions of accessed maps that are not used, is a waste of
`the system's resources and reduces its bandwidth.
`Furthermore, some texture mapping systems are pipelined
`so that various operations are performed simultaneously on
`different object primitives. However, a series of MIP maps
`for a texture can be large. Most systems employ a local
`memory that is capable of storing only one such large series
`of MIP maps at a time. Thus, when there is a switch in the
`texture used in rendering primitives, the system must down(cid:173)
`load a new series of MIP maps. Typically, the data path used
`to load the new texture data into the local memory in the
`texture mapping hardware passes through the system's
`primitive rendering pipeline. Therefore, when a new texture
`is to be mapped, the primitive rendering pipeline must be
`allowed to empty out before the new series of MIP maps can
`be downloaded. Once the series of MIP maps is downloaded,
`the pipeline must again be filled. The necessity of flushing 60
`the primitive rendering pipeline each time a new texture is
`required reduces the system's bandwidth.
`
`SUMMARY OF THE INVENTION
`
`In one illustrative embodiment of the invention, a method
`is provided for managing texture mapping data in a com(cid:173)
`puter graphics system, the computer graphics system includ-
`
`4
`ing a host computer, primitive rendering hardware and a
`primitive data path extending between the host computer
`and the primitive rendering hardware, the host computer
`passing primitives to be rendered by the system to the
`primitive rendering hardware over the primitive data path,
`the host computer having a main memory that stores texture
`mapping data corresponding to the primitives to be
`rendered, the primitive rendering hardware including a local
`texture memory that locally stores the texture mapping data
`10 corresponding to at least one of the primitives to be ren(cid:173)
`dered. In accordance with the illustrative embodiment, the
`method comprises the steps of: (a) when a primitive passed
`to the primitive rendering hardware is to be rendered,
`determining wh