KR101210796B1 - Real time polygonal ambient occlusion method using depth texture - Google Patents

Abstract

PURPOSE: A real time polygonal ambient occlusion method using depth texture is provided to implement a short process time and save resource consumption by sampling depth texture and by an additional calculation. CONSTITUTION: After a depth buffer(110) is generated using a graphics library, a depth texture is generated(110). The sampling of a depth value of a current texel on the depth texture and a neighbor texel of the same is performed(120). The current texel corresponds to a pixel to calculate shadow. By connecting positions of texels having the smallest depth value(130) in the sampling direction, one ambient polygon is generated(130). The shadow of the pixel is calculated using the width of the ambient polygon (140). [Reference numerals] (110) To generate depth texture using a graphics library; (120) To perform the sampling of a depth value of a current texel corresponding to pixel, of which shadow is to be calculated, and its neighbor texel; (130) To generate ambient polygon by connecting positions of texels having the smallest depth value in sampling direction; (140) To calculate the shadow of the pixel using the width of the ambient polygon; (AA) Start; (BB) End

Description

REAL TIME POLYGONAL AMBIENT OCCLUSION METHOD USING DEPTH TEXTURE}

Embodiments of the present invention relate to an ambient occlusion method, which is an illumination algorithm for rendering a realistic image.

The background technology of the present invention is disclosed in the following paper.
1) ZHUKOV S., IONES A., KRONIN G .: An ambient light illumination model. In Proc. Eurographics Workshop Rendering Techniques (1998), pp. 45-55.
2) MITTRING M .: Finding next gen: Cryengine 2. In Proc. ACM SIGGRAPH 2007 Courses (2007), pp. 97-121.
3) BAVOIL L., SAINZ M., DIMITROV R .: Image-space horizon-based ambient occlusion. In ACM SIGGRAPH 2008 talks (2008).
In the field of computer graphics, rendering realistic images is the most important goal and task. To do this, one of the most essential elements is global illumination, and indirect illumination and various effects such as reflection, refraction, scattering, and caustic can be used to express realistic scenes. Do. Methods related to global illumination include radiosity, ray tracing, path tracing, and photon mapping.

However, the conventional methods are difficult to perform real-time rendering that can interact with the user because physical operations are complicated and huge and consume a lot of resources. Moreover, with the advent of methods to improve performance using graphics processing units (GPUs), fast computations on complex scenes are possible, but they are not suitable for the general rendering pipeline built into graphics processing units.

As a result, ambient occlusion has attracted attention as an illumination algorithm that is not able to produce all the effects of global illumination, but can generate shadows quickly and efficiently. Accordingly, the present specification proposes an ambient occlusion method for image rendering.

Polygon's ambient occlusion method is a new lighting algorithm based on ambient occlusion technology.

A polygonal ambient occlusion method is provided for calculating shadows by generating an ambient polygon by sampling depth textures.

A polygonal ambient occlusion method in a graphics processing apparatus according to the present invention may include generating a depth texture representing a depth value of a pixel in screen space; Sampling depth values of neighboring texels neighboring the current texel based on a current texel on the depth texture corresponding to the pixel whose shadow is to be calculated; Generating an ambient polygon by connecting the current texel and the neighboring texels according to the depth value; And calculating a shadow of the pixel by using an area of the polygon of the ambient light.

In the sampling of the depth values of the neighboring texels, sampling may be performed in a plurality of directions about the current texel.

The generating of the ambient light polygon may generate one ambient light polygon by connecting neighboring texels having the lowest depth value among the depth values sampled in each direction with respect to the plurality of directions in which the sampling is performed.

In calculating the shadow of the pixel, the shadow value may be calculated by a ratio of the width of the ambient light polygon to the maximum sampling width of the sampling.

The maximum sampling area may be calculated using Equation 1 or Equation 2, and the shadow value may be calculated using Equation 3.

Equation (1)

Equation 2:

Where m is the maximum sampling width, n is the number of sampling directions, and r is the maximum sampling length.

Equation 3:

Where A is the shadow value of the ambient occlusion, n is the number of sampling directions, i is the order of the sampling direction, p is the position of the current texel, p _i is the value of the texel with the lowest depth value in the i th sampling direction. Position, m is the maximum sampling width)

The polygonal ambient occlusion method according to the present embodiment can quickly calculate the shadow using one depth texture. The screen-space based ambient occlusion method is suitable for applications where real-time rendering is required, such as games, and can produce realistic shadows as quickly as possible. In the case of games, since the ambient occlusion method is added as one intermediate step or post-processing, the polygonal ambient occlusion method according to the present invention is suitable for ensuring real time performance.

Unlike other screen space based methods, the polygonal ambient occlusion method according to the present invention does not require complicated angle calculations or the addition of other techniques, and can be performed only by sampling of depth textures and simple addition operations. The processing time and low resource consumption are advantages.

1 is a flowchart illustrating a real-time polygonal ambient occlusion method of calculating a shadow in real time using a depth texture according to an embodiment of the present invention.
FIG. 2 is an exemplary diagram for describing a process of generating a fragment of an ambient light polygon through sampling of a depth texture according to an embodiment of the present invention.
3 is an exemplary diagram illustrating an ambient light polygon represented in three dimensions in an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Prior to describing the polygonal ambient occlusion method according to the present embodiment, a technique related to the present invention and a general ambient occlusion method will be described.

First, ambient occlusion is a method of obtaining shadows according to the extent to which a point is shielded by surrounding objects, and is an approximation of the global illumination method. It determines how close the object is to represent indirect lighting, such as sun light coming down from the sky, and thus determines the ambient light to represent realistic shadows. In earlier ambient occlusions, virtual rays can be fired in all hemispheres from any location on the object's surface to calculate the number of rays shielded and unshielded by the object as a visibility function.

Is the integral to the shielding calculation advancing in the hemisphere direction, n is the normal vector of the position p , and w is the vector of the shielding calculation direction.

Equation (1) if the ray hits the shield, when holding a light hemispherically direction at a point p on the surface, when visibility function V is 0, no chance is one that calculates a shadow by Monte Carlo integration (Monte Carlo integration) Indicates. In this case, the function max is an attenuation factor using the inner product.

The above-mentioned ambient occlusion method is cheaper than global illumination and is simple to implement, and may improve image quality. In addition, processing time has recently been shortened by the development of a central processing unit (CPU) and a graphics processing unit (GPU), and is widely used in the field of computer games such as screen-space based research.

Representative screen space-based research is screen space ambient occlusion, which is proposed to solve the problem of the existing ambient occlusion which is a long processing time because it is performed on a two-dimensional basis on the graphic processing unit. will be. In general, screen space ambient occlusion uses a depth buffer to perform image processing at high speed without calculating shadows with a three-dimensional model in a scene. Screen space ambient occlusion can calculate shadows using only two-dimensional information by using the depth buffer, and has the advantage of operating independently of the complexity of the scene or moving objects. In other words, screen-space ambient occlusion randomly determines the coordinates of neighboring pixels to sample around the pixel corresponding to the position where the shadow is to be calculated, and then they have a value larger than the depth values stored in the depth buffer. Calculate the ratio of small or small values to determine the degree of shading. As described above, screen space ambient occlusion is performed through a comparison operation between depth values in a depth buffer, and is widely used in fields such as computer games because it operates in real time without pre-computation.

Another screen space-based study is horizon-split ambient occlusion. Horizon Segment Ambient Occlusion calculates the horizon angle using a divided hemisphere, and then connects the horizon angles to create one connected horizon line. Can be calculated.

Hereinafter, a polygonal ambient occlusion method according to an embodiment of the present invention will be described in detail.

The present invention is directed to a polygonal ambient occlusion method for quickly calculating shadows using one depth texture. This method is screen space based and uses only depth textures created using the depth buffer, and unlike conventional screen space based methods, it does not use normal vectors. The present invention begins by considering the depth texture as a kind of heightfield, i.e., the closer the depth value in the depth texture is to 0, the higher the terrain.

1 is a flowchart illustrating a real-time polygonal ambient occlusion method of calculating a shadow in real time using a depth texture according to an embodiment of the present invention.

First, in step 110 of creating a depth texture, a depth buffer is generated using a graphics library, and then a depth texture is created. That is, in step 110, a depth texture may be generated using a depth buffer in which the depth value of the pixel in the screen space is stored. Depth buffers are widely used in the prior art because they can be regarded as abbreviations of three-dimensional models in the scene, and their generation can also be simply implemented using conventional functions.

Next, in operation 120, the depth value of the current texel and its neighboring texels on the depth texture corresponding to the pixel whose shadow is to be calculated is sampled. In the conventional screen space based methods, a random method is used to determine coordinates to sample in a depth texture, but a polygonal ambient occlusion method uses fixed coordinates. For example, in the present embodiment, sampling is performed radially around the current texel, and the maximum distance at which sampling is performed is a constant sampling radius value r . If n sampling directions are used, two adjacent sampling directions have an angle difference of n / 2π around the current texel. When sampling is performed in one direction, sampling is performed at regular intervals, and the depth value is selected by selecting the texel of the coordinates closest to each position.

Next, in operation 130, one ambient light polygon is generated by connecting positions of the texels having the smallest depth value in each sampling direction. Since the depth texture is regarded as a height map in the present invention, the depth values in the depth texture are defined as a kind of height. Therefore, if the depth value is close to zero, it is determined that the terrain has a high height value, which is related to the degree of shielding. When looking at a certain area centered on a point, if the location with the highest height in the area is close to the center point, there is a high degree of shielding, which is likely to result in dark shades. In addition, if the position having the highest height is far from the center point, it is likely that the shadow is not shaded because the degree of shielding is lower than in other cases. On the premise of this, it is assumed that the texel having the lowest depth value among the sampled depth values in each sampling direction has a high degree of shielding, and one polygon formed by connecting the positions of the texels is an ambient light polygon. Therefore, the width of the ambient light polygon is considered to be an unshielded space. The ambient light polygon consists of the same number of pieces as the number of sampling directions, and each piece consists of two sampling directions and the current texel.

FIG. 2 shows three sampling directions, where the gray square is the position of the texel sampled for that direction. The black star marker in the gray square represents the current texel, and the black dot marker is the position of the texel having the lowest depth value among the sampled depth values in the corresponding direction. Connecting two point markers and one star marker creates one piece, and when you create a piece for all the markers and combine them, you create one ambient light polygon. 3 illustrates the ambient light polygon in three dimensions. The generated ambient light polygons are similar to a type of horizon line projected onto a plane.

The final step is to calculate the shadow using the area of the ambient light polygon (140). Since the area of the ambient light polygon can be regarded as an unshielded space, the degree of shading can be determined by dividing it by the total area of the sampling.

In Equation 2, m is the maximum width of the ambient light polygon (ie, the sampling maximum width), n is the number of sampling directions, and r is the maximum sampling length (sampling radius). The maximum width of the ambient light polygon can be defined in two ways as shown in Equation 2, one of which is the width of a circle whose radius is the maximum sampling length r , and the other is the maximum sampling length r that is the vertex of the current texel. The sum of the widths of the pieces with both sides.

In Equation 3, A is the shadow value of the ambient occlusion, n is the number of sampling directions, i is the order of the sampling direction, p is the position of the current texel, p _i has the lowest depth value in the i- th sampling direction The position of the texel, m, is the maximum width of the ambient light polygon calculated in Equation 2. Here, p _i corresponds to the black point marker in FIG. 1, p corresponds to the star marker. In this way, the area of each piece is calculated by calculating the area of the triangle using the two sides and the angle, and the sum is divided by the total area m to obtain the final degree of shading.

In short, the polygonal ambient occlusion method using the depth texture according to the present invention is as follows. In order to calculate the shadow of one pixel, the depth value of the current texel on the depth texture corresponding to the pixel and the depth value of the neighboring texels are sampled. In the depth texture sampling, a neighboring texel may be defined as a texel overlapping a radially spreading sampling direction when the current texel is centered. In the image space, the position of the texel having the lowest depth value among the depth values sampled in the corresponding direction for each sampling direction is stored, and one polygon is generated by connecting the positions of the texels for all the sampling directions. This is called an ambient light polygon, and the shadow is calculated by considering the size of the polygon as an unshielded space. Since the sampling of the depth texture takes most of the calculation, the above method has an advantage that the execution speed is significantly faster than other methods.

The polygonal ambient occlusion method may be applied to a graphic processing device for rendering a realistic image in the field of computer graphics, and each process (110 to 140 of FIG. 1) included in the polygonal ambient occlusion method is described above. It may be performed by the graphics processing device.

Although a schematic diagram of a graphic processing apparatus in which the polygonal ambient occlusion method according to the present invention is performed is omitted, it may include a processor and a memory. In this case, the memory generates a depth texture representing the depth value of the pixel in the screen space, and then samples the depth value of the neighboring texels adjacent to the current texel based on the current texel on the depth texture corresponding to the pixel whose shadow is to be calculated. A program including an instruction for connecting the current texel and the neighboring texels to generate an ambient light polygon according to the sampled depth value and calculating a shadow of the pixel using the width of the ambient light polygon may be stored. In addition, the processor is a device for processing according to an instruction of a program stored in the memory, and may include a microprocessor such as a CPU.

As described above, according to the present embodiment, it is possible to provide a polygonal ambient occlusion method for quickly calculating a shadow using one depth texture. The real-time polygonal ambient occlusion method according to the present invention generates one ambient light polygon composed of several pieces by sampling depth textures, and calculates the degree of shading by considering the area of the ambient light polygon as an unshielded space. Can be. Therefore, the present invention can be performed only by texture sampling and simple additional operation without any additional method, and thus shows much faster execution speed than existing methods.

Methods according to an embodiment of the present invention may be implemented in program instruction form that can be executed by various computer systems and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the medium may be those specially designed and constructed for the present invention or may be available to those skilled in the art of computer software. In addition, the above-described file system can be recorded in a computer-readable recording medium.

As described above, the present invention has been described by way of limited embodiments and drawings, but the present invention is not limited to the above embodiments, and those skilled in the art to which the present invention pertains various modifications and variations from such descriptions. This is possible.

Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined by the equivalents of the claims, as well as the claims.

Claims (5)

In the polygonal ambient occlusion method in the graphics processing apparatus,
Generating a depth texture indicative of a depth value of a pixel in screen space;
Sampling depth values of neighboring texels neighboring the current texel based on a current texel on the depth texture corresponding to the pixel whose shadow is to be calculated;
Generating an ambient polygon by connecting the current texel and the neighboring texels according to a depth value of the neighboring texels; And
Calculating a shadow of the pixel using an area of the ambient light polygon
Including,
Calculating the shade of the pixel,
Computing a shadow value by the ratio occupied by the width of the ambient light polygon from the maximum sampling width of the sampling proceeds,
The maximum sampling width is calculated using Equation 1 or Equation 2,
The shadow value is calculated using Equation 3
Polygonal ambient occlusion method characterized in that.
Equation 1:

Equation 2:

Where m is the maximum sampling width, n is the number of sampling directions, and r is the maximum sampling length.
Equation 3:

Where A is the shadow value of the ambient occlusion, n is the number of sampling directions, i is the order of the sampling direction, p is the position of the current texel, p _i is the value of the texel with the lowest depth value in the i th sampling direction. Position, m is the maximum sampling width) The method of claim 1,
Sampling the depth values of the neighboring texels,
Sampling in the direction of n radial lines (n is an integer of 2 or more) centering on the current texel
Polygonal ambient occlusion method characterized in that. The method of claim 2,
Generating the ambient light polygon,
Generating one ambient light polygon by connecting neighboring texels having the lowest depth value among the depth values sampled in each direction with respect to the n directions in which the sampling is performed;
Polygonal ambient occlusion method characterized in that. delete delete

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