Abstract:
In accordance with some embodiments, a full per sample coverage mask may be used for a subset of the pixels in the tile, thereby enabling pixels that belong to multiple depth ranges to be handled. This makes the depth bounds a tighter fit for the true depth range of the tile and improves hierarchical depth culling efficiency when MSAA is used.

Description:
BACKGROUND 
     This relates generally to graphics processing and, specifically, to occlusion culling. 
     Culling means “to remove from flock,” and in graphics, it boils down to removing work that does not alter the final image. This includes, for example, view frustum culling, where objects that are outside the view frustum are not further processed, since they will not affect the final image. 
     In maximum depth culling, often called hierarchical occlusion culling, the maximum depth, z max , of a tile is stored and maintained per tile. If the estimated conservative minimum depth of a triangle inside a tile is greater than the tile&#39;s z max , then the triangle is completely occluded inside that tile. In this case, the per-sample depth values do not need to be read from memory, and no further processing is needed within the tile for that triangle. This technique is sometimes called z max -culling. In addition, one may also store the minimum depth, z min , of the depths in a tile, and avoid depth reads if a triangle fully covers a tile, and the triangle&#39;s estimated conservative maximum depth is smaller than the z min , in which case the triangle will overwrite all depths in the tile (assuming no alpha/stencil test etc). 
     The z max  is computed from the per-sample depths in a tile. Ideally, the z max -value of a tile should be recomputed every time a depth whose value is z max  is overwritten. 
     A depth culling unit stores the z max -representation, which may be accessed through a cache, for example. A tile may hold plane equations from the triangle that covers the tile, and for subsequent triangles culling can be done immediately against that representation (either against the evaluated depths from the plane equations, or by computing z max  of the plane equations inside the tile). When the tile can no longer maintain this representation, due to storage requirements or other criteria, the plane equations may be replaced by one or many z min - and z max -values for the entire tile, or for subtile regions of the tile. For example, an 8×8 tile could hold two z min  and two z max  for each of the 4×8 subtile regions. Unless a feedback is used, sending computed z max  values back from the depth buffer unit to the hierarchical occlusion culling unit, the z max -values needs to be conservatively updated and will in general stay the same, unless an entire subtile is fully covered by a triangle. 
     Multi-sampled anti-aliasing (MSAA) is a type of supersampling. Generally, the renderer evaluates a fragment program, once per pixel, and only truly supersamples the depth and stencil values. In general, multi-sampling refers to a special case of supersampling where only some components of the final image are not fully supersampled. 
     Anti-aliasing is any technique to combat aliasing in a sampled signal to smooth images rendered by computer generated imagery. Attempts to overcome jaggies which are stair step like lines that should have been smooth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments are described with respect to the following figures: 
         FIG. 1  is a depiction showing how depth values are recreated from a plane equation according to one embodiment; 
         FIG. 2  is a graph of a plane equation for one embodiment; 
         FIG. 3  is a flow chart for one embodiment; 
         FIG. 4  is a schematic depiction for one embodiment; 
         FIG. 5  is a flow chart for another embodiment; 
         FIG. 6  is a system depiction according to one embodiment; and 
         FIG. 7  is a front elevational view of one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     In accordance with some embodiments, reduced precision may be used when storing depth plane values for partially covered tiles while using full precision for fully covered tiles. However, the reduced precision is only used if the reconstructed depth values are identical to what would have been produced using a full precision depth plane in one embodiment. This allows the use of a depth plane representation with fewer bits in most cases, thereby freeing up bits for storing additional information such as coverage masks or additional depth planes. This allows more tiles to be represented in the depth culling unit, thereby reducing depth buffer bandwidth in some embodiments. 
     Depth plane equations (Ref, D x , D y ) may be represented in a high precision floating point format. When the depth value of a sample is evaluated, the plane equation is evaluated as z(x,y)=Ref+x·D x +y·D y , where (x,y) is the sample coordinate. All computations are performed in the internal high precision format similar to IEEE double precision float and the result is finally rounded to a single precision (32 bit) IEEE float value. If a tile (typically an 8×4 rectangle of pixels) is determined to be completely covered by a triangle, it may be stored in plane equation form. Since the plane equation is enough to recreate the depth values of all samples exactly, the depth buffer is not updated, saving bandwidth each time a tile can be stored in plane mode. An alternative lower precision plane equation may be used as long as the depth values evaluated for all (covered) samples are identical to the depth values used with the higher precision plane equation, after rounding to single precision float depths.  FIG. 1  (A-C) is an example of how a depth value is computed. 
     In the plane equation, the deltas, (D x , D y ) are typically stored in 32-bit single precision and the reference value is stored in higher precision as shown in  FIG. 1A . The deltas are then converted to the higher precision format as shown in  FIG. 1B . Finally, when the depth value is composited, the reference value and deltas are normalized to the same exponent by shifting mantissas, as shown in  FIG. 1C , and finally added together to composite the final depth value. Only the upper 23 bits remain after the final conversion to floating point, and the remaining bits are only used to ensure correct rounding. In a compacted plane representation, in addition to storing the upper 23 bits, a number of guard bits are used to ensure correct result after rounding. The number of guard bits required to ensure correct rounding varies based on per-sample depth data and can be difficult to compute. As an optimization, one may start from the allowed bit-budget of a compressed tile and subtract storage needed for all other data. This directly gives the guard bits available within the current budget, and then one may test if the compacted representation ensures the correct result after rounding. Typically, the deltas have much smaller exponents than the reference value, and therefore, the mantissa bits of the deltas that fall outside the guard bits range may be omitted. An example is illustrated in  FIG. 10 . 
       FIG. 1  illustrates how depth values are re-created from the plane equation. The example illustrates re-creating the depth value z(1,1)=Ref+D x +D y .  FIG. 1A  shows the original plane equation. The deltas, (D r , D y ) are stored in 32-bit single precision and the reference value is stored in higher precision (e.g. 64 bits). In  FIG. 1B , the delta values are converted to the same high precision format as the reference value. In  FIG. 10 , the exponents are normalized. All values are represented with the same exponent and the mantissas are shifted accordingly. Only the upper 23) bits remain after the final conversion to single precision float. In addition, a number of extra guard bits are stored to ensure a correct result after rounding. The bits falling to the right of the guard bits&#39; border can be removed saving a total of 37 bits in this example. 
     Most tiles are representable with 6-12 guard bits. The actual number of saved bits depend on the relative exponents of Ref, D x , and D y , and typically varies between 10 and 60 for relevant workloads. The saved bits may be used to store additional data including but not limited to: use a compressed coverage mask, encode two planes overlapping a single tile, store additional min/max values or data aiding culling of the regions not covered by the triangle. 
     The values of the plane equation received from the rasterizer are evaluated to determine a compact representation for the signs and exponent values. Then, it is determined if the per-sample coverage mask can be compressed using either horizontal or vertical breaks, which is a compressed bit-mask representation described in detail later. Since the bit budget is typically very tight, a configuration with one or two pixel horizontal breaks, or one pixel vertical break may be used. After storing signs, exponents, and the compressed per-sample coverage mask, the remaining bits may be used for encoding the lower precision mantissa bits of the depth plane equation. A simple equation is solved to determine how many guard bits can be spent on the mantissas of Ref, D x , and D y . Then the precision is reduced by rounding them to the allowed number of bits, similar to  FIG. 1C , giving us lower precision values            f,           and          .
     The exact plane equation (line G in  FIG. 2 ) is evaluated at given samples, and rounded to float (the crosses in  FIG. 2 ). An interval of full precision values, {circumflex over (z)}=[z, z ], that would all round to the given sample&#39;s 32-bit depth value are computed. These intervals are back projected to the reference point (x=0) using the reduced precision deltas, to obtain an interval            f of possible reference values, where the back projection is given by
 
           f =[ Ref , Ref ]= {circumflex over (z)}−x·{tilde over (D)}   x   −y·{tilde over (D)}   y   =[ z −x·{tilde over (D)}   x   −y·{tilde over (D)}   y   , z −x·{tilde over (D)}   x   −y·{tilde over (D)}   y ].

     A final possible interval may be computed by taking the maximum of all samples&#39;  Ref , ceiled to the nearest quantized value for the lower precision representation (dictated by how many guard bits one can afford) and the minimum of  Ref , floored to nearest quantized value. The tile is representable if the interval is not empty,  Ref &lt; Ref , and in such a case one may pick            f as any quantized value in          f. If the tile is not compressible, then some other representations, such as z max  mode may be used and all depth values are sent to backend z for further processing. The method for adapting the plane equation described herein only adapts the          f value. However, it is possible to tune all the values (         ,         ,         ) in the plane equation, potentially allowing more tiles to be compressed, but at a greater computational cost.
     Referring to  FIG. 3 , compact plane equation sequence  10  may be implemented in software, firmware and/or hardware. In software and firmware embodiments, it may be implemented by computer executed instructions stored in one or more non-transitory computer readable media such as magnetic, optical or semiconductor storages. 
     The sequence begins as indicated at block  11  by analyzing the plane equation to determine a compact representation for the signs and exponent values as indicated in block  12 . Then it is determined if the per sample coverage mask can be compressed as indicated at diamond  13 . 
     Next the signs, exponents and compressed per sample coverage mask are stored as indicated in block  14 . Lower precision mantissa bits of the depth plane equation are encoded as indicated in block  15 . 
     The number of needed guard bits can be spent on mantissas can be determined as indicated in block  16 . Finally the exact plane equation is adapted to make sure that all the values are correct as indicated in block  18 . 
     Referring to  FIG. 4 , a depth buffer architecture  20  includes a rasterizer  22  to identify which pixels lie within the triangle currently being rendered. In order to maximize memory coherency for the rest of the architecture, it is often beneficial to first identify which tiles (a collection of W×H pixels) overlap the triangle. When the rasterizer finds a tile that partially overlaps the triangle, it distributes the pixels in that tile over a number of pixel pipelines  24 . The purpose of each pixel pipeline is to compute the depth and color of a pixel. Each pixel pipeline contains a depth test unit  26 , responsible for discarding pixels that are occluded by the previously drawn geometry. The depth unit  28  includes a memory  32 , in one embodiment, that is a random access memory. It also includes a tile table cache  30  temporarily storing the z max -mask representation for each tile and backed by the memory  32 , a tile cache  41  which is also backed by the memory  32  and temporarily stores per-sample depth values for rapid access, optionally a z max -feedback computation  36  which updates the z max  representation in the tile table  30  each time a tile is evicted from the tile cache  41 , a compressor  35 , and a decompressor  37 , as well as a coverage mask buffer  34 . The tile table cache stores the z max  representation and header information, for example one or more flags indicating which compression algorithm is used to compress a tile of depth values, separately from the depth buffer data. 
     The compressor  35 , in general, compresses the tile depth values to a fixed bit rate and fails if it cannot represent the tile in a given number of bits without information loss. When writing a depth tile to memory, the compressor with the lowest bit rate is typically selected that succeeds in compressing the tile without excessive information being lost. The flags in the tile table are updated with an identifier unique to that compressor and compressed data is written to memory. When a tile is read from memory, the compressor identifier is read from the tile table and the data is decompressed using the corresponding decompression algorithm  37 . A buffer  34  may store the coverage mask as well. 
     The mask algorithm used to compact the partial coverage mask, which may be stored in the saved bits, operates as follows. First, assume that each pixel-row in a tile is comprised of contiguous regions of pixels either fully covered or fully not covered, henceforth called a “solid region”, and store the mask of such regions using one bit only. Each solid region is separated by a “break region”, which is a region where a bit is stored for every sample to indicate whether it is covered. After each break, an additional bit is stored to indicate if the following solid region that it belongs is covered. 
     In some embodiments, different configurations may be used for the breaks. For example, a single two pixel wide break may be supported for each row within the desired bit budget. Another alternative is to support two independent breaks, where the breaks are only one pixel wide, giving fewer pixels but greater flexibility in where the pixels are positioned. In practice, best performance is gained by testing a few different break configurations while compressing, picking the one that fits within the least number of bits, and storing a few header bits to indicate which configuration was used for a particular tile. 
     The process of finding the solid regions and the break regions may be implemented as follows. First, a variable L equal to the coverage mask of the first sample in the first pixel is set. Then the sequence scans over all samples in all pixels, for example from left to right. Once a sample with a coverage mask that differs from L is found, the enclosing pixel is marked as a break B. After explicitly storing mask bits for all samples in all pixels in the break region (starting from B and stretching over a number of pixels), L is reinitialized to be the mask bit of the first sample in the first pixel after the break region, followed by an iterative search for the next break. The mask is not compressible any row requires more breaks than allowed by the configuration. 
     It is also possible to swap axes and specify the breaks for vertical columns. Another variant to searching for breaks in column or in row order, is to have other space filling curves that fully or partially cover the tiles such as Hilbert or Morton curves. Nothing needs to be altered in these cases and the pixel order may be implicit from the mode. Furthermore, it is possible to assume that all solid regions to the left or right of the break region belong to the same z max  layer. For the scenarios where this is common, a mode can be used where the layer information can be encoded in a single bit. 
     In accordance with some embodiments, a coverage mask compaction sequence  70  shown in  FIG. 5  may be implemented in software, firmware and/or hardware. In software and firmware embodiments it may be implemented by computer executed instructions stored in one or more non-transitory computer readable media such as a semiconductor, magnetic or optical storage. In one embodiment, the random access storage  32  may be used for this purpose as shown in  FIG. 4 . 
     The sequence  70 , shown in  FIG. 5 , begins by scanning each row/column to find the pixels in which a coverage mask changes as indicated in block  78 . These are the pixels that need to be represented with a per-sample mask. Next the coverage mask representation is changed (block  80 ) as described above. 
     A check at diamond  82  determines if the tile is not representable using the selected mode. If it is not, then an option must be selected at block  84 . One option is to go back to block  78  using a different row/column orientation. Another option is to go back to block  80  with a different parameter setting. If no more variants are available, then another representation such as the original, per pixel z max  mode or some other representation must be used as indicated in block  86 . 
       FIG. 6  illustrates an embodiment of a system  700 . In embodiments, system  700  may be a media system although system  700  is not limited to this context. For example, system  700  may be incorporated into a personal computer (PC), laptop computer, ultra-laptop computer, tablet, touch pad, portable computer, handheld computer, palmtop computer, personal digital assistant (PDA), cellular telephone, combination cellular telephone/PDA, television, smart device (e.g., smart phone, smart tablet or smart television), mobile internet device (MID), messaging device, data communication device, and so forth. 
     In embodiments, system  700  comprises a platform  702  coupled to a display  720 . Platform  702  may receive content from a content device such as content services device(s)  730  or content delivery device(s)  740  or other similar content sources. A navigation controller  750  comprising one or more navigation features may be used to interact with, for example, platform  702  and/or display  720 . Each of these components is described in more detail below. 
     In embodiments, platform  702  may comprise any combination of a chipset  705 , processor  710 , memory  712 , storage  714 , graphics subsystem  715 , applications  716  and/or radio  718 . Chipset  705  may provide intercommunication among processor  710 , memory  712 , storage  714 , graphics subsystem  715 , applications  716  and/or radio  718 . For example, chipset  705  may include a storage adapter (not depicted) capable of providing intercommunication with storage  714 . 
     Processor  710  may be implemented as Complex Instruction Set Computer (CISC) or Reduced Instruction Set Computer (RISC) processors, x86 instruction set compatible processors, multi-core, or any other microprocessor or central processing unit (CPU). In embodiments, processor  710  may comprise dual-core processor(s), dual-core mobile processor(s), and so forth. The processor may implement the sequences of  FIGS. 3 and 5  together with memory  712 . These sequences may be performed in some embodiments by a graphics processor of the graphics subsystem  715 . 
     Memory  712  may be implemented as a volatile memory device such as, but not limited to, a Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), or Static RAM (SRAM). 
     Storage  714  may be implemented as a non-volatile storage device such as, but not limited to, a magnetic disk drive, optical disk drive, tape drive, an internal storage device, an attached storage device, flash memory, battery backed-up SDRAM (synchronous DRAM), and/or a network accessible storage device. In embodiments, storage  714  may comprise technology to increase the storage performance enhanced protection for valuable digital media when multiple hard drives are included, for example. 
     Graphics subsystem  715  may perform processing of images such as still or video for display. Graphics subsystem  715  may be a graphics processing unit (GPU) or a visual processing unit (VPU), for example. An analog or digital interface may be used to communicatively couple graphics subsystem  715  and display  720 . For example, the interface may be any of a High-Definition Multimedia Interface, DisplayPort, wireless HDMI, and/or wireless HD compliant techniques. Graphics subsystem  715  could be integrated into processor  710  or chipset  705 . Graphics subsystem  715  could be a stand-alone card communicatively coupled to chipset  705 . 
     The graphics and/or video processing techniques described herein may be implemented in various hardware architectures. For example, graphics and/or video functionality may be integrated within a chipset. Alternatively, a discrete graphics and/or video processor may be used. As still another embodiment, the graphics and/or video functions may be implemented by a general purpose processor, including a multi-core processor. In a further embodiment, the functions may be implemented in a consumer electronics device. 
     Radio  718  may include one or more radios capable of transmitting and receiving signals using various suitable wireless communications techniques. Such techniques may involve communications across one or more wireless networks. Exemplary wireless networks include (but are not limited to) wireless local area networks (WLANs), wireless personal area networks (WPANs), wireless metropolitan area network (WMANs), cellular networks, and satellite networks. In communicating across such networks, radio  718  may operate in accordance with one or more applicable standards in any version. 
     In embodiments, display  720  may comprise any television type monitor or display. Display  720  may comprise, for example, a computer display screen, touch screen display, video monitor, television-like device, and/or a television. Display  720  may be digital and/or analog. In embodiments, display  720  may be a holographic display. Also, display  720  may be a transparent surface that may receive a visual projection. Such projections may convey various forms of information, images, and/or objects. For example, such projections may be a visual overlay for a mobile augmented reality (MAR) application. Under the control of one or more software applications  716 , platform  702  may display user interface  722  on display  720 . 
     In embodiments, content services device(s)  730  may be hosted by any national, international and/or independent service and thus accessible to platform  702  via the Internet, for example. Content services device(s)  730  may be coupled to platform  702  and/or to display  720 . Platform  702  and/or content services device(s)  730  may be coupled to a network  760  to communicate (e.g., send and/or receive) media information to and from network  760 . Content delivery device(s)  740  also may be coupled to platform  702  and/or to display  720 . 
     In embodiments, content services device(s)  730  may comprise a cable television box, personal computer, network, telephone, Internet enabled devices or appliance capable of delivering digital information and/or content, and any other similar device capable of unidirectionally or bidirectionally communicating content between content providers and platform  702  and/display  720 , via network  760  or directly. It will be appreciated that the content may be communicated unidirectionally and/or bidirectionally to and from any one of the components in system  700  and a content provider via network  760 . Examples of content may include any media information including, for example, video, music, medical and gaming information, and so forth. 
     Content services device(s)  730  receives content such as cable television programming including media information, digital information, and/or other content. Examples of content providers may include any cable or satellite television or radio or Internet content providers. The provided examples are not meant to limit embodiments of the invention. 
     In embodiments, platform  702  may receive control signals from navigation controller  750  having one or more navigation features. The navigation features of controller  750  may be used to interact with user interface  722 , for example. In embodiments, navigation controller  750  may be a pointing device that may be a computer hardware component (specifically human interface device) that allows a user to input spatial (e.g., continuous and multi-dimensional) data into a computer. Many systems such as graphical user interfaces (GUI), and televisions and monitors allow the user to control and provide data to the computer or television using physical gestures. 
     Movements of the navigation features of controller  750  may be echoed on a display (e.g., display  720 ) by movements of a pointer, cursor, focus ring, or other visual indicators displayed on the display. For example, under the control of software applications  716 , the navigation features located on navigation controller  750  may be mapped to virtual navigation features displayed on user interface  722 , for example. In embodiments, controller  750  may not be a separate component but integrated into platform  702  and/or display  720 . Embodiments, however, are not limited to the elements or in the context shown or described herein. 
     In embodiments, drivers (not shown) may comprise technology to enable users to instantly turn on and off platform  702  like a television with the touch of a button after initial boot-up, when enabled, for example. Program logic may allow platform  702  to stream content to media adaptors or other content services device(s)  730  or content delivery device(s)  740  when the platform is turned “off.” In addition, chip set  705  may comprise hardware and/or software support for 5.1 surround sound audio and/or high definition 7.1 surround sound audio, for example. Drivers may include a graphics driver for integrated graphics platforms. In embodiments, the graphics driver may comprise a peripheral component interconnect (PCI) Express graphics card. 
     In various embodiments, any one or more of the components shown in system  700  may be integrated. For example, platform  702  and content services device(s)  730  may be integrated, or platform  702  and content delivery device(s)  740  may be integrated, or platform  702 , content services device(s)  730 , and content delivery device(s)  740  may be integrated, for example. In various embodiments, platform  702  and display  720  may be an integrated unit. Display  720  and content service device(s)  730  may be integrated, or display  720  and content delivery device(s)  740  may be integrated, for example. These examples are not meant to limit the invention. 
     In various embodiments, system  700  may be implemented as a wireless system, a wired system, or a combination of both. When implemented as a wireless system, system  700  may include components and interfaces suitable for communicating over a wireless shared media, such as one or more antennas, transmitters, receivers, transceivers, amplifiers, filters, control logic, and so forth. An example of wireless shared media may include portions of a wireless spectrum, such as the RF spectrum and so forth. When implemented as a wired system, system  700  may include components and interfaces suitable for communicating over wired communications media, such as input/output (I/O) adapters, physical connectors to connect the I/O adapter with a corresponding wired communications medium, a network interface card (NIC), disc controller, video controller, audio controller, and so forth. Examples of wired communications media may include a wire, cable, metal leads, printed circuit board (PCB), backplane, switch fabric, semiconductor material, twisted-pair wire, co-axial cable, fiber optics, and so forth. 
     Platform  702  may establish one or more logical or physical channels to communicate information. The information may include media information and control information. Media information may refer to any data representing content meant for a user. Examples of content may include, for example, data from a voice conversation, videoconference, streaming video, electronic mail (“email”) message, voice mail message, alphanumeric symbols, graphics, image, video, text and so forth. Data from a voice conversation may be, for example, speech information, silence periods, background noise, comfort noise, tones and so forth. Control information may refer to any data representing commands, instructions or control words meant for an automated system. For example, control information may be used to route media information through a system, or instruct a node to process the media information in a predetermined manner. The embodiments, however, are not limited to the elements or in the context shown or described in  FIG. 6 . 
     As described above, system  700  may be embodied in varying physical styles or form factors.  FIG. 7  illustrates embodiments of a small form factor device  800  in which system  700  may be embodied. In embodiments, for example, device  800  may be implemented as a mobile computing device having wireless capabilities. A mobile computing device may refer to any device having a processing system and a mobile power source or supply, such as one or more batteries, for example. 
     As described above, examples of a mobile computing device may include a personal computer (PC), laptop computer, ultra-laptop computer, tablet, touch pad, portable computer, handheld computer, palmtop computer, personal digital assistant (PDA), cellular telephone, combination cellular telephone/PDA, television, smart device (e.g., smart phone, smart tablet or smart television), mobile internet device (MID), messaging device, data communication device, and so forth. 
     Examples of a mobile computing device also may include computers that are arranged to be worn by a person, such as a wrist computer, finger computer, ring computer, eyeglass computer, belt-clip computer, arm-band computer, shoe computers, clothing computers, and other wearable computers. In embodiments, for example, a mobile computing device may be implemented as a smart phone capable of executing computer applications, as well as voice communications and/or data communications. Although some embodiments may be described with a mobile computing device implemented as a smart phone by way of example, it may be appreciated that other embodiments may be implemented using other wireless mobile computing devices as well. The embodiments are not limited in this context. 
     The processor  710  may communicate with a camera  722  and a global positioning system sensor  720 , in some embodiments. A memory  712 , coupled to the processor  710 , may store computer readable instructions for implementing the sequences shown in  FIGS. 3 and 5  in software and/or firmware embodiments. 
     As shown in  FIG. 7 , device  800  may comprise a housing  802 , a display  804 , an input/output (I/O) device  806 , and an antenna  808 . Device  800  also may comprise navigation features  812 . Display  804  may comprise any suitable display unit for displaying information appropriate for a mobile computing device. I/O device  806  may comprise any suitable I/O device for entering information into a mobile computing device. Examples for I/O device  806  may include an alphanumeric keyboard, a numeric keypad, a touch pad, input keys, buttons, switches, rocker switches, microphones, speakers, voice recognition device and software, and so forth. Information also may be entered into device  800  by way of microphone. Such information may be digitized by a voice recognition device. The embodiments are not limited in this context. 
     Various embodiments may be implemented using hardware elements, software elements, or a combination of both. Examples of hardware elements may include processors, microprocessors, circuits, circuit elements (e.g., transistors, resistors, capacitors, inductors, and so forth), integrated circuits, application specific integrated circuits (ASIC), programmable logic devices (PLD), digital signal processors (DSP), field programmable gate array (FPGA), logic gates, registers, semiconductor device, chips, microchips, chip sets, and so forth. Examples of software may include software components, programs, applications, computer programs, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, subroutines, functions, methods, procedures, software interfaces, application program interfaces (API), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. Determining whether an embodiment is implemented using hardware elements and/or software elements may vary in accordance with any number of factors, such as desired computational rate, power levels, heat tolerances, processing cycle budget, input data rates, output data rates, memory resources, data bus speeds and other design or performance constraints. 
     The following clauses and/or examples pertain to further embodiments: 
     One example embodiment may be a method comprising storing a depth plane representation for fully covered tiles, and storing a depth plane representation for partially covered tiles at lower precision than for fully covered tiles stored at higher precision. The method may also include determining whether reconstructed depth values for partially covered tiles are the same as obtained with higher precision after rounding. The method may also include using bits saved through the lower precision representation to store a compressed coverage mask. The method may also include using bits saved through the lower precision representation to encode two planes overlapping a single tile. The method may also include storing signs, exponents and compressed per sample coverage mask. The method may also include encoding lower precision mantissa bits of a depth plane equation. The method may also include adapting the lower precision plane representation to make samples&#39; depth values identical to the corresponding higher precision plane representation. The method may also include using a graphics processor to store a depth plane representation. 
     In another example embodiment may be at least one or more non-transitory computer readable media storing instructions executed by a processor to perform a sequence comprising storing a depth plane representation for tiles that are fully covered by a primitive, and storing a depth plane representation for partially covered tiles at lower precision than for fully covered tiles stored at higher precision. The media may include determining whether reconstructed depth values for partially covered tiles are the same as values with the higher precision representation after rounding. The media may include using bits saved through the lower precision representation to store a compressed coverage mask. The media may include using bits saved through the lower precision representation to encode two planes overlapping a single tile. The media may include storing signs, exponents and compressed per sample coverage mask. The media may include encoding lower precision mantissa bits of a depth plane equation. The media may include adapting the lower precision plane representation to make samples&#39; depth values identical to the corresponding higher precision plane representation. 
     Another example embodiment may be an apparatus comprising a processor to store a depth plane representation for fully covered tiles and to store a depth plane representation for partially covered tiles at lower precision than for fully covered tiles stored at higher precision, and a memory coupled to said processor. The apparatus may include said processor to determine whether reconstructed depth values for partially covered tiles are the same as obtained with higher precision after rounding. The apparatus may include said processor to use bits saved through the lower precision representation to store a compressed coverage mask. The apparatus may include said processor to use bits saved through the lower precision representation to encode two planes overlapping a single tile. The apparatus may include said processor to store signs, exponents and compressed per sample coverage mask. The apparatus may include said processor to encode lower precision mantissa bits of a depth plane equation. The apparatus may include said processor to adapt the lower precision plane representation to make samples; depth values identical to the corresponding higher precision plane representation. The apparatus may include wherein said processor is a graphics processor. The apparatus may include a rasterizer. The apparatus may include a display communicatively coupled to the processor. The apparatus may include a battery coupled to the processor. The apparatus may include firmware and a module to update said firmware. 
     The graphics processing techniques described herein may be implemented in various hardware architectures. For example, graphics functionality may be integrated within a chipset. Alternatively, a discrete graphics processor may be used. As still another embodiment, the graphics functions may be implemented by a general purpose processor, including a multicore processor. 
     References throughout this specification to “one embodiment” or “an embodiment” mean that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation encompassed within the present disclosure. Thus, appearances of the phrase “one embodiment” or “in an embodiment” are not necessarily referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be instituted in other suitable forms other than the particular embodiment illustrated and all such forms may be encompassed within the claims of the present application. 
     While a limited number of embodiments have been described, those skilled in the art will appreciate numerous modifications and variations therefrom. It is intended that the appended claims cover all such modifications and variations as fall within the true spirit and scope of this disclosure.