Abstract:
The disclosure provides for a dynamic skydome system for generating dynamic atmospheric and/or sky effects for use in electronic visual media, such as for games and movies. The features of the dynamic skydome system of the disclosure include mimicking real-world behavior of the sky through a 24 hour cycle, providing a physically based rendering model with multiple atmospheric scatterings; simulating astronomically correct celestial bodies; producing god rays; providing aerial perspectives; and dynamically lighting volumetric clouds.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119 from Provisional Application Ser. No. 61/831,115, filed Jun. 4, 2013, the disclosure of which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure provides for a system of generating real-time dynamic atmospheric and/or sky based effects for electronic visual media. 
     BACKGROUND 
     Developments in atmospheric or sky effects for electronic visual media have had a profound impact on many types of media and have revolutionized animation, movies and the video game industry. 
     SUMMARY 
     The disclosure provides for a dynamic skydome system that generates dynamic atmospheric and/or sky effects for use in electronic visual media, such as for games and movies. The features of the dynamic skydome system include, but not limited to, mimicking real-world behavior of the sky through a 24 hour day night cycle, providing a physically based rendering model with multiple atmospheric scatterings; simulating astronomically correct sun, stars, and moon; producing god rays; providing aerial perspectives; and dynamically lighting volumetric clouds. 
     Disclosed herein is a system for generating dynamic atmospheric effects for electronic visual media (i.e., a dynamic skydome system). The dynamic skydome system disclosed herein provides innovative methods for generating dynamic lighting effects for atmospheric objects, sky coloring, and scene presentation that are of a quality which greatly exceed those produced by current methods in electronic visual media. 
     In a certain embodiment, the disclosure provides a dynamic skydome system that performs dynamic actual lighting for all accumulated objects in one rendering pass, and/or calculates the color of the sky or atmosphere in the vertex shader, wherein the dynamic skydome system is carried out using a device comprising a graphics processing pipeline. In a further embodiment, the disclosure provides for a dynamic skydome system which comprises: lighting one or more objects using depth encoding and/or blending; rendering the one or more objects into a single impostor; and lighting the one or more objects in a single rendering pass. 
     In another embodiment, the disclosure provides a dynamic skydome system that performs actual lighting for all accumulated objects (e.g., clouds, celestial bodies, and atmospheric particles, such as fog, haze, or smoke) in one rendering pass comprising one or more steps of: rendering one or more objects accumulated depth and weight into a texture buffer using a blending algorithm to perform actual accumulation; reading the accumulated depth and depth weight from the texture buffer once all of the one or more objects are rendered to the screen and smoothing the read data using hardware texture bilinear interpolation; reconstructing the depth of the one or more objects using the smoothed read data; and/or performing actual lighting for all accumulated objects in one rendering pass by using the reconstructed depth to reconstruct position of the one or more objects. 
     In a particular embodiment, the disclosure provides for lighting one or more objects by implementing a blending algorithm comprising: (1) DepthAcc=OldDepthAcc*(1−newDepthWeight)+NewDepth*NewDepthWeight; (2) DepthWeightAcc=OldDepthWeightAcc*(1−newDepthWeight)+NewDepthWeight; and (3) Final depth=DepthAcc/DepthWeightAcc. In a further embodiment, a two channel floating-point 16-bit render target stores the accumulated depth and normalization weight of multiple particles for each pixel of impostor. In an alternate embodiment, a four channel floating-point 16-bit render target stores the accumulated depth and normalization weight of multiple particles for each pixel of an impostor and also stores normal or per-particle ambient occlusion data. 
     In a particular embodiment, a dynamic skydome system disclosed herein calculates the color of a sky or an atmosphere in the vertex shader by moving the texture coordinates and texture read into the vertex shader, and utilizing the vertex to pixel shader hardware interpolators to perform the interpolation in the 4 th  dimension. 
     In another embodiment, the disclosure provides a dynamic skydome system that calculates the color of the sky and/or atmosphere in the vertex shader comprising one or more steps of: reading the low-frequency 4-dimensional data from the 3-dimensional texture using hardware linear interpolation in the vertex shader, writing the data from the previous step to a hardware interpolator with linear interpolation enabled, interpolating data for every pixel being generated by rasterizer using the hardware interpolator, reading the pixel data into the pixel shader from the hardware interpolator; and using the data to calculate sky and/or atmosphere color. 
     In a certain embodiment, a dynamic skydome system disclosed herein can perform one or more of the following: mimicking the real-world behavior of a sky through a 24 hour day night cycle; performing physically-based rendering with multiple atmospheric scatterings; simulating of celestial bodies that are astronomically correct; generating god rays; providing aerial perspectives; and dynamically lighting volumetric clouds. 
     In a further embodiment, the dynamic skydome system is carried out using a device comprising a graphics processing pipeline, such as a computer (e.g., a video game console) or flight simulator. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a block diagram of a computing device environment for practicing an illustrative embodiment of the present invention. 
         FIG. 2  is a block diagram of an illustrative simulation environment for practicing an embodiment of the present invention on the computing device of  FIG. 1 . 
         FIG. 3  is a diagrammatic view of an illustrative skydome mesh for practicing an embodiment of the present invention. 
         FIG. 4  is a flow diagram depicting steps performed in an illustrative method of a graphics processing pipeline in an illustrative embodiment of the present invention. 
         FIG. 5  is a flow diagram(s) depicting steps performed in an illustrative method of the dynamic skydome system disclosed herein for implementing lighting effects for atmospheric objects. 
         FIG. 6  is a flow diagram(s) depicting steps performed in an illustrative method of the dynamic skydome system disclosed herein for calculating sky or and/or atmosphere color in the vertex shader instead of the pixel shader. 
         FIG. 7  presents an atmospheric effect generated by a dynamic skydome system of the disclosure of god rays. 
         FIG. 8  presents an atmospheric effect generated by a dynamic skydome system of the disclosure of volumetric clouds depicted in a test level. 
         FIG. 9  presents an atmospheric effect generated by a dynamic skydome system of the disclosure of earth&#39;s atmosphere as approached from space. 
         FIG. 10  presents a cloud lighting effect generated by the dynamic skydome system of the disclosure. 
         FIG. 11  demonstrates typical errors in lighting due to using flat imposter positions. 
         FIG. 12  provides depth re-construction of a cloud by using the depth encoding and depth weighting method disclosed herein. 
         FIG. 13  presents an example of a cloud lighting effect generated by using the depth encoding and depth weighting method disclosed herein. 
     
    
    
     DETAILED DESCRIPTION 
     As used herein and in the appended claims, the singular forms “a,” “and,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “value” includes a plurality of such values and reference to “polygon” includes reference to one or more polygons and equivalents thereof known to those skilled in the art, and so forth. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. 
     The realistic simulation of outdoor scenes presents significant challenges. A common approach to simulate outdoor scenes is by modeling a dome (i.e., a skydome), to provide the impression of a sky and objects typically seen in the sky, such as clouds, moon, stars, and sun. A skydome can also be used to simulate outdoor scenes from hypothetical environments, such as atmospheres from imaginary worlds and moons. 
     Clouds play an important role in simulating outdoor environments. Realistic-looking clouds can be one of the most compelling graphical components of outdoor scenes, especially for real-world applications such as flight simulators and movie productions. The appearance of clouds is affected by the light cast by the sun and filtered from the sky, which must be reflected in the cloud shading. Moreover, in the real world, clouds do not remain static, they are dynamic. They move across the sky, from areas of moisture and unstable air, and dissipate when these conditions abate. Therefore, the presentation of clouds in electronic visual media should accurately reflect their dynamic nature. 
       FIG. 1  depicts an environment suitable for practicing an illustrative embodiment of the dynamic skydome system of the disclosure. The environment includes a computing device  102  having memory  106 , on which software according to one embodiment of the present invention may be stored, a processor (“CPU”)  104  for executing software stored in the memory  106 , and other programs for controlling system hardware. The memory  106  may comprise a computer system memory or random access memory such as DRAM, SRAM, EDO RAM, etc. The memory  106  may comprise other types of memory as well, or combinations thereof. A human user may interact with the computing device  102  through a visual display device  114  such as a computer monitor, which may used to display a graphical user interface (“GUI”). The computing device  102  may include a video adapter  107  for providing for I/O operations with the visual display device  114 . 
     Additionally, the computing device  102  may include a graphics card/processor  105  for handling one or more graphics processing functions of the computing device for displaying graphics, images, user interfaces, or any other type of visual element to the display device  114 . In one embodiment, the computing device  102  includes an expansion card  105  that interprets drawing instructions sent by the central processor (“CPU”)  104 , processes them via a dedicated graphics processor  105 , and writes the resulting frame data to the frame buffer, also called or otherwise is part of the video adapter  107 . The graphics processor  105  may perform one or more graphics processing functions such as bitmap transfers and painting, window resizing and repositioning, line drawing, font scaling and polygon drawing. The graphics processor  105  may be designed to handle these tasks in hardware at far greater speeds than the software running on the system&#39;s central processor  104 . The graphics processor  105  may be any type of graphics processor, such as any graphic processing chip provided or manufactured by Nvidia Corporation of Santa Clara, Calif., or Advanced Micro Devices, Inc. of Sunnyvale, Calif. The graphics processor  105  may be part of any type of graphics card, such as any of the graphics cards incorporating the Nvidia graphics processor, such as Nvidia&#39;s series of GeForce® graphics chip, or the Radeon® series of graphics cards from Advanced Micro Devices. One ordinarily skilled in the art will recognize and appreciate the various types and wide range of graphics card/processors  105  that may be used in the computing device  102 . 
     Although generally described as a graphics processor  105 , or a processor dedicated to graphics processing functions, the processor  105  can be any type of general purpose processor (“GPP”), or any other type of integrated circuit, such as a Field Programmable Gate Array (“FPGA”), Programmable Logic Device (“PLD”), or Application Specific Integrated Circuit (“ASIC”). Furthermore, although the illustrative embodiment of the computing device  102  is described with a separate processor  105  for graphics related processing, the central processor  104  may provide for such graphics related processing. Alternatively, the computing device  102  may have multiple processors to distribute processing of computing tasks, along with any graphics processing functions. In one embodiment, the graphics card/processor  105  of the computing device  102  has multiple graphics processors, such as for example the dual GPU graphics card provided or manufactured by Giga-Byte Technology, Co. LTD of Taipei Hsien, Taiwan. In another embodiment, the graphics processor  105  performs graphics-oriented operations but also other computations, such as any operation of the processor  104 , such as a CPU. One ordinarily skilled in the art will recognize and appreciate that any type of computing device with any type of processor may be used to perform the operations of the present invention as described herein. 
     In  FIG. 2 , the dynamic skydome system disclosed herein provides a simulation environment  120  for generating, modeling, creating, editing or otherwise handling, manipulating and processing images. In brief overview, the simulation environment  120  provides a platform for image based design, processing, and simulation of outdoor and/or indoor scenes including naturally occurring atmospheres and terrains, naturally occurring dynamic systems, along with any man-made objects, structures and/or system. The simulation environment  120  may include one or more images  215  representing visually, graphically, or otherwise, a scene, such as an outside scene. For example, the image  215  may comprise a photo realistic, near photo realistic or otherwise substantially realistic representation of an outside scene including an atmosphere, such as a sky, sun, stars, moon, and clouds. 
     The simulation environment  120  includes a graphical user interface for interactively creating and working with images  215  and may also provide for simulating, editing, configuring, and processing the images  215 . The simulation environment  120  may read, save, interpret, or otherwise process image files in any format known to one ordinarily skilled in the art. 
     The simulation environment  120  may comprise any suitable configuration mechanism  250  for configuring any elements and properties of the image  215 , the simulation and rendering of one or more images  215 , and/or the simulation environment  120 . The configuration mechanism  250  may comprise any type of user interface, such as a graphical user interface or command line interface. As such, it may comprise any user interface mechanisms such as menu items, forms, toolbars, etc. as known by ordinarily skilled in the art to provide a user interface to receive user input with regards to configuration. 
     The simulation environment  120  also comprises one or more libraries  240  to provide for the processing of images and at least a portion of the operations of the present invention described herein. Although described as libraries  240 , the libraries  240  may take the form of any type of executable instructions capable of performing the operations described herein. 
     In an exemplary embodiment, the libraries  240  may include Direct3D or DirectX SDK manufactured by Microsoft Corporation of Redmond, Wash., to provide an application programming interface (“API”) in the operating system to graphics and sounds functionality provided by the hardware of the computing device  102 . In some embodiments, the libraries  240  include any application programming interfaces, APIs, supporting the OpenGL standards and specifications as known by those ordinarily skilled in the art. 
     Additionally, the libraries  240  may include any portion of the CG Toolkit manufactured by Nvidia, Inc. of Santa Clara, Calif., wherein Cg is a high level language for graphics programming. The libraries  240  may also include any portion of executable instructions manufactured by The Freetype Project located at www.freetype.org, which is a high quality, portable font engine, and in other embodiments, may include any suitable font engine. Additionally, the libraries  240  may include any executable instructions of the Developer&#39;s Image Library (DevIL) manufactured by Denton Woods. 
     The libraries  240  of the simulation environment  120  may include any programming related APIs and libraries, such as STLport manufactured by STLport Consulting of San Francisco, Calif., Xerces of the Apache XML Project provided by the Apache Software Foundation, Inc. of Forest Hill, Md., and any publicly available libraries authored by Beman Dawes and David Abrahams, located at boost.org. Additionally, to support file and data compression related functionality in the simulation environment  120 , the libraries  240  may include any type of compression libraries such as the Zlib library provided by The GNU Project of the Free Software Foundation of Boston, Mass. Furthermore, the libraries  240  may include windowing and graphical widgets for graphics APIs and engines such as Crazy Eddie&#39;s GUI System, located at cegui.org.uk, which is a publicly available object orientated tool for building graphical user interface systems. 
     The simulation environment  120  comprises a simulation engine  220  and rendering mechanism  210 . The simulation engine  220  provides the graphics processing  225  functionality and instructions of the present invention for image simulation and the rendering of the image  215  via the rendering mechanism  210 . The rendering mechanism  210  includes means and mechanisms as known by those ordinarily skilled in the art to cause the rendering of the image  215  to the visual display device  114  of the computing device  102 . In the rendering stage of graphics/image processing, typically performed by the graphics card/processor  105  in conjunction with the video adapter  107 , the pixels are drawn to the video display device  114 . 
     The graphics processing  225  portion of the simulation engine  220  comprises shader programs, such as pixel shader program  230  and vertex shader program  235 . The terms “shaders” may be used instead of program or shader program to refer to the portions of executable instructions that program certain parts of the graphics processing pipeline. The computational frequency that may be supported in graphics related hardware, such as a graphics card/processor  105 , is per vertex and per pixel/fragment. As such, there are two different kinds of shaders: vertex shaders  235  and pixel shaders  230 . A pixel shader  230  provides graphics processing on a pixel basis, and a vertex shader  235  provides graphics processing on a vertex basis. 
     Pixel shaders  230  may also include or be referred to as fragment shaders. As known by those ordinarily skilled in the art, fragments are all the points of three-dimensional scene that are projected onto a two-dimensional xy-plane, such as in an OpenGL® based implementation. A fragment contains information such as position and texture coordinates, and several fragments can be added together when displayed to a pixel on the screen. 
     As known by those ordinarily skilled in the art, a vertex shader  235  is a set of graphics processing instructions used to add special effects to objects in a three-dimensional (3D) environment by performing mathematical operations on an object&#39;s vertex data. Objects in a 3D scene, such as those provided by the image  215  of the simulation environment  210 , may be described using polygons such as triangles, which in turn are defined by their vertices. Vertex data refers to the data set identifying and/or describing the vertices of the triangles representing the 3D scene. A vertex shader  235  can change the position or any other attributes of a vertex. Vertex shaders  235  may get executed for each vertex that passes through the graphics processing pipeline. 
     Pixel shaders  230  as known by those ordinarily skilled in the art are graphics processing instructions that calculate effects on a per-pixel basis. In some embodiments, the pixel shader  230  receives as input computational results from a vertex shader  235 , such as the vertex position. Generally in the art, the pixel shader  230  uses input provided by the vertex shader  235  and any other attributes, such as user-defined attributes, generated or modified colors and texture coordinates, and combine the information to form a final color value that gets passed to the final stages of rendering. However, in a particular embodiment, the dynamic skydome system disclosed herein calculates the sky and/or atmosphere color in the vertex shader  235  instead of the pixel shader  230  by utilizing hardware interpolators between the vertex shader  235  and the pixel shader  230 . 
     With the graphics cards/processor  105  of the computing device  102  being programmable, the pixel shader  230  and vertex shader  235  can comprise customized executable instructions to provide desired graphics processing of vertex and pixel/fragment data associated with the image  215 . In an exemplary embodiment, the simulation environment  210  provides at least a portion of the real-time execution of the realistic approximation of natural atmospheric lighting phenomena of the present invention via one or more vertex shaders  235  and/or pixel shaders  230 . 
     The simulation environment  120 , and any portion thereof, can be an application, module, library, software component, or any other type of computer program or executable instruction which is designed to and capable of executing the functionality of the simulation environment  120  as described herein. Additionally, the simulation environment  120 , and any portion thereof, may be executed as an application, program, service, process, task, or any other form of execution unit known by those skilled in the art. Furthermore, the simulation environment  120 , and any portion thereof, may be designed to run on any type of processor  104 ,  105  microprocessor, operating system, or computing device  102 . 
     The simulation environment  120  can be capable of and configured to operate on and take advantage of different processors of the computing device  102 . For example, the simulation environment  120  can run on a 32 bit processor of one computing device  102  and a 64 bit processor of another computing device  102 . Additionally, the simulation environment  120  can be capable of and configured to operate with and take advantage of different graphical cards/processors  105  of the computing device  102 . For example, any shader program  230 ,  235  of the simulation engine  220  may be designed to operate on and take advantage of any type of graphical processor  105 . Furthermore, the simulation environment  120  can operate on computing devices  102  that can be running on different processor architectures with different graphical processing cards and processors in addition to different operating systems. One ordinarily skilled in the art will recognize the various combinations of operating systems, processors, or graphical cards that can be running on the computing device  102 . In summary, the simulation environment  120  may be deployed across a wide range of different computing devices, different operating systems, and different processors in various configurations. One ordinarily skilled in the art will appreciate the various ways the present invention may be practiced in a computing device. 
     In a particular embodiment, for the dynamic skydome system disclosed herein, the image  215  provided by the simulation environment  120  comprises a realistic graphical and/or visual representation of an outdoor scene including a natural atmospheric environment. In one embodiment, the image  215  is a photo realistic, near photo realistic or otherwise substantially realistic representation of the outdoor scene. The scene may comprise any combination of naturally occurring and/or man-made objects. In a brief overview, the scene may comprise a terrain and an atmosphere. The terrain may include any physical features and characteristics of a planet&#39;s surface, such as the earth or any other orbiting celestial object. As such, the terrain may include a landscape with any type of land mass and one or more bodies of water. For example, the land mass may include any type of mountain or hill, or any range of mountains and hills. The bodies of water may be any type of water such as a puddle, pond, lake, sea or ocean. Additionally, the terrain may include any man-made objects and/or structures, such as vehicles, buildings, houses, and bridges. For example, the terrain may provide a realistic representation of any man-made structures or objects seen in any city, town, or country side known in the world. Also, the terrain may include any flora or any other type of animal or creatures, either living or fictional. Additionally, the terrain may include any fauna, or any other type of plant-life or vegetation, either actual or fictional. 
     The atmosphere represented by the scene of the image  215  may include the sky, a sun, one or more clouds, one or more celestial objects, and one or more types of atmospheric particles. The clouds may be any type and/or any portion of a formation of a cloud. The atmosphere may represent any portion of the atmosphere of the earth, or any other planet or orbiting celestial land mass. The celestial objects may be any naturally occurring objects in the atmosphere, sky, or space, such as the sun, moon, planets and stars. The atmosphere generally represents air molecules, such as clean air molecules, that may be available in any portion of the sky or atmosphere of the scene. The atmosphere may include any man-made objects such as aircraft or satellites. Additionally, the atmosphere may include any flora, or any other type of animal or creature, either living or fictional. The atmospheric particles represent portions of the atmosphere other than air molecules, such as ice, rain, water droplets, crystals, snow, fog, haze, dust, smoke, pollutants, and any other particles, solid or otherwise, that may be an element of the atmosphere and/or sky. 
     Although the scene is generally described as a photo or near photo realistic representation of known and existing terrain and atmosphere, the scene may provide a photo or visual realistic representation of fictional terrain and atmosphere. Instead of the terrain and/or atmosphere of the scene of the image being provided by terrain data related to actual measurements of terrain and atmospheric components related to the earth, the terrain and/or atmosphere may be generated or otherwise provided to realistically represent an imaginary scene. As such, the scene may not be a scene of a terrain and atmosphere existing in the world but nevertheless may look as an actual existing terrain and atmosphere due to the photorealistic or visual realism of the image  215 . 
     In order to provide for photorealistic or otherwise visually realistic representation of the scene, the effect of the physics of light and optics needs to be considered for the many objects of the terrain and/or atmosphere, and the dynamic interactions between them. For example, the effect of light from the sun and the sky along with shadows casted by clouds need to be considered to determine the color of a rendered object in the image  215  as seen by a viewer from a certain viewing position with respect to a view of the scene. 
     In another aspect, the present invention relates to the simulation and rendering of the natural atmospheric lighting phenomena associated with the scene of the image  215 , and any objects of the scene. 
     As a realistic representation, image  215  represents a three-dimensional (3D) view of an outdoor scene. This 3D representation needs to be projected and rendered to a two-dimensional (2D) display of the visual display device  114  of the computing device  102 . In a brief overview, a scene comprises a terrain mesh and a skydome mesh  420  integrated to form a geometric polygon representation of a scene which includes image  215 . The terrain mesh provides a mesh for the terrain portion of a scene and the skydome mesh  420  for the atmospheric (e.g., sky) portion of the scene. In an exemplary embodiment, the atmosphere&#39;s geometry is defined as the set of all points below an infinite plane with some user-specified height above the viewer, although more complex models can be used as known by those ordinarily skilled in the art. 
       FIG. 3  depicts an illustrative wire screen rendering of the skydome mesh  420 . For illustrative purposes and by way of example, the skydome mesh  420  comprises multiple triangle primitives  430 . In computer graphics processing, a primitive  430  is a fundamental shape or object used primarily in the construction of more complex objects. In the example of  FIG. 3 , the skydome mesh  420  is a complex polyhedron made up of a series of connected triangle primitives  430 . Each corner of a triangle primitive  430  forms a vertex  440  and each triangle primitive  430  has three vertices  440 . A vertex  440  is the point where the sides of a polygon meet. That is, a vertex is a point in 3D space that defines a corner of one or more polygons, such as the triangle primitive  430 . Although the present invention is illustrated using a triangle primitive  430 , any type of suitable shape or polygon may be used for geometric representation of an image  215 . Increasing the number of primitives or polygons of a sky dome mesh  420  enables more detailed and complex geometric representation of a scene. As such, increasing the number of polygons geometrically representing the image  215  improves the visual realism of rendering a scene. 
     In one embodiment, the invention provides techniques for determining the color of the triangle primitives  430  of a skydome mesh  420  to graphically render a scene to realistically represent natural atmospheric lighting. These techniques enable the graphical processing and rendering of the simulation of the natural atmospheric lighting to occur at sufficiently high enough rates to allow for a realistic representation of atmospheric objects in a scene. Furthermore, the dynamic skydome system disclosed herein not only provides for real-time rendering speeds but also provides for photo realistic, near photo realistic, visually realistic or otherwise substantially realistic simulation of natural atmospheric lighting. As such, the present invention provides a simulation environment  120  that can simulate and render images  215  in real-time and in a continuous manner to show the realistic visual effects of changes in natural atmospheric lighting upon one or more images  215 . 
       FIG. 4  depicts an illustrative method  500  of graphics processing of the present invention practiced in conjunction with the illustrative embodiment of  FIG. 2 . The illustrative method  500  represents at least a portion of the functionality of a typical graphics processing architecture, also referred to and known in the art as a graphics processing pipeline. The graphics processing pipeline depicted by illustrative method  500  may consider and perform any graphics processing functions known by those ordinarily skilled in the art in fixed-function or programmable graphics related hardware. The illustrative method  500  of the present invention performs primitive processing at step  510 , vertex processing at step  515 , pixel processing at step  520  and rendering at step  525 . Primitive processing of illustrative step  510  may include any type of processing performed by the graphics card/processor  105  and/or the graphics processing portion  225  of the simulation engine  220  on a primitive  430 , such as the triangle primitives of the skydome mesh  420 . 
     In an exemplary embodiment, the graphics processing pipeline depicted by illustrative method  500  is programmable via shaders  230  and  235 . As such, a vertex shader  255  of the graphics processing  225  portion of the simulation engine  220  may provide desired vertex processing operations at step  515  to provide for the realistic simulation and real-time rendering of the natural atmospheric lighting of the dynamic skydome system disclosed herein. Likewise, a pixel shader  230  may provide desired pixel/fragment processing operations at step  520  to provide for the realistic simulation and real-time rendering of the natural atmospheric lighting. 
     At step  525  of the illustrative method, the final colors  450  of each of the primitives  430  of the mesh  400  representation of the image  215  are rendered as impostors to a visual display device  114 . Via the rendering mechanism  210 , impostors are written and/or read to the frame buffer of the video adapter  107  of the computing device  102 . There may be hundreds to thousand or more polygons for each frame of a scene which must be updated and transmitted to the frame buffer. The frames are further processed, converted or transformed into suitable analog and or digital output signals of the visual display device  114 . The rate of transfer to the frame buffer and/or visual display device  114  is known as frame rate and is measured in frames per second (fps). Each frame of a scene must be updated and transmitted through the frame buffer at a certain rate to give the illusion of movement. 
     In order to accelerate rendering, imposters have generally been utilized. Imposters are transparent polygons (i.e., billboards) with an opaque texture mapped onto them. Impostors are used to accelerate rendering by exploiting frame-to-frame coherence. Impostors are particularly well suited to clouds, even in circumstances under which they cannot be applied to the rendering of polygonal geometry. By using impostors, the dynamic skydome system of the disclosed can render cloudy scenes of hundreds of clouds and hundreds of thousands of particles at very high frame rates. For example, the dynamic skydome system disclosed herein can be used to render multiple cloud images into a single imposter and provide lighting effects for each cloud image in a single rendering pass (e.g., see  FIG. 10 ). 
     Steps for rendering an imposter into a scene can comprise: cleaning the texture buffer; setting up the view for rendering the object; rendering a part of the view (the size of the objects bounding box) onto a texture that is stored in texture memory; and placing a billboard in the virtual world and rendering the imposter texture onto it. Impostors can be updated dynamically. With this strategy, if the user moves slowly or comes to a complete halt, the image can be progressively refined to the correct image—that is, the one that would have been obtained by rendering the original geometry. A disadvantage of dynamically generated impostors arises from the potentially unbounded complexity of the geometry that needs to be converted into the image-based representation. As the updates are done on the fly, they must fit into the frame-time budget allocated for generating the image  215 . 
     The dynamic skydome system disclosed herein can visually and realistically simulate and render in real-time natural atmospheric lighting and related phenomena for one or more images in an outdoor scene at high frame rates per second. Further, the dynamic skydome system disclosed herein provides methods to approximate the visual effects of natural atmospheric lighting and related phenomena that are visually realistic which are computed in real-time to render frames of a scene at high frame rates per second. The dynamic skydome system presented herein accounts for the light scattering effects due to sunlight and ambient light in relation to objects, atmospheric particles and other scene elements. 
     The dynamic skydome system disclosed herein can provide images and simulations having visually realistic representations of sunlight at any time of day, including from dawn to twilight, along with accurate shadowing effects. The dynamic skydome system of the disclosure can also provide images and simulations having visually realistic representations of night or darkness cycles, including the presentation of celestial objects such as stars and moons. 
     Additionally, the dynamic skydome system of the disclosure provides visually realistic representations of a wide range of cloud formations, resulting cloud cover over the landscape of a scene, and shadows cast by clouds on elements of the scene. Furthermore, the present invention provides a realistic simulation of the visual effects from light scattering by the cloud cover, such as god rays, and also provides visually realistic simulation of atmospheric particles of water (i.e., rain, hail, snow, mist, and fog) including accurate reflections, refractions, and turbulence. In a particular embodiment, an atmospheric particle represents a portion of one or more of the following: a cloud, rain, ice, dust, fog, haze, smoke, pollutants, and air. In a further embodiment, at least one of the one or more atmospheric objects represents one or more of the following: a sky, a cloud, a celestial body, and a man-made item. In yet a further embodiment, the dynamic skydome system of the disclosure can determine the appropriate color for an object by calculating a realistic approximation of a visible effect on the natural atmospheric lighting phenomenon from one or more of the following: in scattering light from atmospheric particles, out scattering light from atmospheric particles, sunlight illumination, ambient illumination, cloud appearance, cloud density, cloud lighting, and cloud shadowing. In another embodiment, the dynamic skydome system disclosed herein includes depicting the movement of at least one atmospheric object in the scene. 
     One of the many challenges with lighting a large number of visually depicted objects is that each object is an imposter and the imposter is flat. Accordingly, to calculate a reasonable position for lighting each pixel is extremely difficult (e.g., see  FIG. 11 ). The disclosure provides a dynamic skydome system that overcomes these difficulties by providing an innovative way to calculate lighting each pixel in imposter space. In a particular embodiment, the disclosure provides for a dynamic skydome system which comprises one or more steps of: lighting one or more objects using depth encoding and/or blending; rendering the one or more objects into a single impostor; lighting the one or more objects in a single rendering pass; and/or calculating the color of the sky or atmosphere in the vertex shader. In a further embodiment, a dynamic skydome system performs actual lighting for all accumulated objects in one rendering pass (e.g., see  FIG. 5 ) comprising the steps of: rendering one or more objects accumulated depth and weight into a texture buffer using blending state to perform actual accumulation  300 , reading the accumulated depth and depth weight from the texture buffer once all of the one or more objects are rendered to the screen and smoothing the read data using hardware texture bilinear interpolation  320 , reconstructing the depth of the one or more objects using the smoothed read data  330 , performing actual lighting for all accumulated objects in one rendering pass by using the reconstructed depth to reconstruct position of the one or more objects  340 . 
     In yet a further embodiment, a dynamic lighting system disclosed herein stores the accumulated depth and normalization weight of multiple particles (e.g., cloud particles) for each pixel of impostor by a computer implementing a linear depth re-construction algorithm of: 
     (1) DepthAcc=OldDepthAcc*(1−newDepthWeight)+NewDepth*NewDepthWeight 
     (2) DepthWeightAcc=OldDepthWeightAcc*(1−newDepthWeight)+NewDepthWeight 
     (3) Final depth=DepthAcc/DepthWeightAcc 
     In yet a further embodiment, a computer stores the accumulated depth and the normalization weight using a two channel floating-point 16-bit render target. Typically, when read by a computer the content of the two channel floating-point 16-bit render target will be bilinear filtered. While the division of values is not linear the values are substantially consistent. In another embodiment, a computer stores the accumulated depth and the normalization weight using a four channel floating-point 16-bit render target. By utilizing a four channel floating-point 16-bit render target, in addition to bilinear filtering, a normal or per-particle ambient occlusion data may also be stored by a computer so as to allow for more complex lighting effects. The resulting Final depth value can then be applied to an image, such as a representation of clouds (e.g., see  FIG. 12 ). An example of the implementation of the linear depth re-construction method of the dynamic skydome system disclosed herein is demonstrated by the lighting of the clouds in  FIG. 13 . 
     The disclosure further provides for a dynamic skydome system disclosed herein which calculates sky or and/or atmosphere color in the vertex shader instead of the pixel shader (see  FIG. 6 ). The dynamic skydome system disclosed herein calculates texture coordinates to read the textures, and uses 4-dimensional interpolation. Hardware only provides 3-dimensional interpolation of texture data. Universally, the 4 th  dimension is interpolated in the pixel shader. By moving the texture coordinates and the texture read into the vertex shader the system utilizes the vertex to pixel shader hardware interpolators to perform the interpolation in the 4 th  dimension thereby increasing the calculation&#39;s efficiency. In a further embodiment, the sky color calculated in the vertex shader is of the same or higher quality as sky color calculated in a pixel shader. In particular embodiment, the disclosure provides a dynamic skydome system that calculates sky and/or atmosphere color comprising the steps of: reading the low-frequency 4-dimensional data from the 3-dimensional texture using hardware linear interpolation in the vertex shader  350 , writing the data from the previous step to a hardware interpolator with linear interpolation enabled  360 , interpolating data for every pixel being generated by rasterizer using the hardware interpolator  370 , reading the pixel data into the pixel shader from the hardware interpolator  380 , using the data to calculate sky and/or atmosphere color  390 . In a further embodiment, additional data processing may be performed during the reading of data step  350 . 
     In an alternate embodiment, the dynamic skydome system disclosed herein performs the interpolation in the 4 th  dimension using the pixel shader. 
     A number of embodiments have been described herein. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of this disclosure. Accordingly, other embodiments are within the scope of the following claims.