KR100914915B1 - A low cost view-volume clipping method and an apparatus therefor - Google Patents

Abstract

The present invention provides a low cost view-volume clipping method.

The view-volume clipping method according to the present invention comprises the steps of: performing far-near clipping with respect to the far-near plane of the view-volume; Setting a polygon and determining the polygon scanning start point (x _i , y _i ) based on a horizontal and vertical coordinate boundary of a view port in the one-far projected plane of the near-clipped view-volume; Scanning vertices of the starting point and horizontal vertices to a horizontal boundary of the view port based on the determined starting point (x _i , y _i ); And scanning the vertices of the starting point and the vertical direction to the vertical boundary of the view port based on the determined starting point (x _i , y _i ).

With this arrangement, by considering the viewport boundary in determining the starting point in the polygon setting step and determining the next scanning position in the scanning step, the view-volume clipping is performed even if the clipping operation is performed only for the near-far plane. This becomes possible.

Therefore, according to the view-volume clipping apparatus according to the present invention, it is possible to reduce the time and hardware cost of the conventional conventional clipping.

Description

LOW COST VIEW-VOLUME CLIPPING METHOD AND AN APPARATUS THEREFOR}

The present invention relates to a graphics processing method, and more particularly to a clipping processing method.

The present invention is derived from a study conducted as part of the IT growth engine technology development project of the Ministry of Information and Communication and the Ministry of Information and Communication Research and Development. ].

Three-dimensional (hereinafter referred to as "3D") graphics technology is widely used in various devices that communicate with users through a screen such as a multimedia device, a game machine, a personal computer (PC), and the scope of use thereof. Is gradually widening. 3D graphics processing can be divided into two stages: geometry processing and rasterization. Geometry processing includes processing such as transformation, lighting, clipping, perspective projection, etc., and scanning line processing includes processing such as interpolation, texture mapping, and the like. It includes.

Among them, a main process of the 3D graphics processing is shown in FIG. 1, which includes a clipping block for deleting a group out of a scene from a vertex data group and final vertices at that time. A viewport mapping block for setting the coordinate values of the polygons, a polygon setting block for defining an outline of each polygon, and a scanning block for pixelating the polygons are shown.

Here, "clipping" refers to a view volume (a view of volume 200a, 200b) with the vertex position of the eye of the observer 220 as shown in FIG. 2 in a display area that is a virtual 3D space where the viewer sees a 3D image. Excludes images that are outside of the image, includes images that are inside view-volumes 200a and 200b, and images that span the boundary of view-volume 200, leaving only the portion that enters inside view-volume 200. Say cut work.

In this case, the image to be clipped is decomposed into polygons, which are geometric units, in order to rasterize only the parts included in the view volume, and vertices that exist outside the view volume. There is a significant computational load to remove and create new vertices to replace it.

In addition, the clipping process with this considerable computational load must be performed separately for each of the six planes of the view-volume, and must also be considered to maintain the connectivity of the established polygons after the clipping.

Therefore, this conventional clipping method has a problem of causing high cost in terms of latency and hardware.

In order to solve the above problem, in the present invention, instead of clipping all six faces of the view-volume in the clipping block, only clipping is performed on near-far clipping planes, and polygon setting is performed. We propose a method and apparatus for reducing the amount of computation and the time required for clipping the entire view-volume by adding simple functions to blocks and scanning blocks.

Thus, the view-volume clipping method according to the present invention comprises the steps of: performing far-near clipping on the far-near plane of the view-voldume; Setting a polygon based on horizontal and vertical coordinate boundary values of the viewport in the one-far projected plane of the near-clipped view-volume and determining the polygon scanning start point (x _i , y _i ) ; Scanning vertices of the starting point and horizontal vertices to a horizontal boundary of the view port based on the determined starting point (x _i , y _i ); And scanning the vertices of the starting point and the vertical direction to the vertical boundary of the view port based on the determined starting point (x _i , y _i ).

In addition, the view-volume clipping apparatus 400 according to the present invention receives a vertex data group and performs clipping for far-near clipping on the far-near plane of the view-volume. Way; Means for viewport transforming a perspective-near-projected plane of the perspective-closed view-volume; Means for setting a polygon based on horizontal and vertical coordinate boundaries of the viewport and determining a polygon scanning start point (x _i , y _i ); And means for determining a scanning progress direction in the horizontal or vertical direction of the viewport relative to the determined starting point (x _i , y _i ) and scanning the polygon vertices to a horizontal or vertical coordinate boundary of the viewport. Characterized in that it comprises a.

According to the view-volume clipping method according to the present invention, by determining the starting point in the polygon setting step and the next scanning position in the scanning step, by considering the view port boundary, the view-volume only with the clipping operation for the near-far plane Clipping is now possible.

According to the view-volume clipping method according to the present invention, it is possible to reduce the amount of computation required for the conventional clipping process, and also to implement clipping which causes high cost in terms of latency and hardware.

1 is a diagram schematically showing a part of a three-dimensional graphics rendering process.

2A and 2B are diagrams illustrating the view-volume.

3 is a block diagram of a view-volume clipping apparatus according to an embodiment of the present invention.

4 is a diagram illustrating a view port.

5 is a diagram illustrating the flow of operation of the scanning means of FIG. 4.

Explanation of symbols on the main parts of the drawings

400: clipping device 410: clipping means

420: normalized conversion means 430: view port mapping means

440: polygon setting means 450: scanning means

Hereinafter, a view-volume clipping method and a view-volume clipping apparatus using the same will be described in detail with reference to the accompanying drawings of FIGS. 3 to 5.

3 shows a schematic configuration diagram of a clipping apparatus 300 according to the present invention.

The graphic apparatus 300 according to the present invention includes a clipping means 310, a normalization transformation means 320 for normalizing vector data, and a viewport mapping means for setting coordinate values of final vertices at a corresponding time point. 330, polygon setting means 340 for defining a scanline of each polygon, and scanning means 350 for pixelating the polygons.

Here, the input of the clipping means 310 is vertex data represented by clip coordinates after the projection transform as shown in FIG. 3. The view-volume in this clip coordinate can be defined as follows.

-w _c ≤ x _c ≤ w _c

-w _c ≤ y _c ≤ w _c

-w _c ≤ z _c ≤ w _c

(Where x _c , y _c , z _c , w _c are real numbers, and x _c , y _c , z _c , w _c are vertex coordinates after the projection transformation)

Therefore, the equations of the six planes of the view-volume can each be defined as follows.

x _c = -w _c , x _c = w _c

y _c = -w _c , y _c = w _c

z _c = -w _c , z _c = w _c

(Where x _c , y _c , z _c , w _c are real numbers, and x _c , y _c , z _c , w _c are vertex coordinates after the projection transformation)

Of these, z _c = w _c corresponds to the near plane and z _c = -w _c corresponds to the far plane of the view-volume. Perspective-plane in the view-volume of the orthogonal projection (202a, 204a) and perspective projection in the view-volume of Fig. 2 (a) and (b) respectively. 202b and 204b are shown.

The clipping means 310 of the clipping apparatus according to the present invention performs a clipping operation on the circular plane and the near plane as described above.

In addition, the normalization transforming means 320 and the viewport converting means 330 perform the same functions as general normalization converting means and the viewport converting means, by which the coordinates of the three-dimensional vertices are two-dimensional in the viewport. Mapping to the plane.

In FIG. 4, such view ports are (0, 0), (0, H _s -1), (W _s -1, H _s -1) and (W _s -1, 0)-where W _s is The horizontal width of the resolution of the display screen, H _s, is defined as a square consisting of four points-the vertical height of the resolution of the display screen, in which the polygon setting means 340 and the scanning means 350 according to the invention We will use the bounds of the viewport above.

Specifically, polygon setup means 340 performs the necessary operations to interpolate the vertex data. In this process, the polygon setup means 340 determines a scanning start point on screen coordinates based on an x-axis or y-axis coordinate value among the vertices of the polygon. In the conventional implementation, since the scanning start point is determined after clipping for all six view-volumes, there are no vertices outside the upper, lower, left, and right boundaries of the viewport, but the polygon setting according to the present invention is performed. Since the vertices input to the means 340 are input values where only clipping to the perspective plane is done, these vertices may exist outside the viewport. Accordingly, the polygon setup means 340 determines the scanning start point in consideration of the top, bottom, left and right boundaries of the viewport.

In more detail, when the polygon is described as an example of a 'triangle', three vertices forming a triangle are defined as V ₀ (x ₀ , y ₀ ), V ₁ (x ₁ , y ₁ ), and V ₂ (x ₂ , y ₂ ), and if y ₀ is greater than y ₁ and y ₂ , or equal to one of y ₁ or y ₂ and greater than the other, then the scanning start point (x _i , y _i ) is defined as

x _i = [x ₀ ], if 0 ≤ x ₀ <W _s

= 0, if x ₀ <0

= W _s -1, if x ₀ ≥ W _s

Where square brackets indicate fractional truncation where [x] = n for all x where n ≦ x <n + 1 when n is an integer, W _s represents the horizontal width of the display screen's resolution,

y _i = [y ₀ ], if 0 ≤ y ₀ <H _s

= 0, if y ₀ <0

= H _s -1, if y ₀ ≥ H _s

Where [y] = n for all y where n ≦ x <n + 1, and H _s represents the vertical height of the resolution of the display screen.

Next, the scanning means 350 performs a function of scanning, that is, generating pixel data by interpolating the vertex data. The scanning means 350 generates all the pixels present on the line containing the current scanning position and then starts the next line. In this case, it is assumed that scanning means maintains consistency with the polygon setting means 340 described above and scans while descending from the upper line to the lower line of the viewport. According to one embodiment of the invention, the flow of operation of such scanning means 350 is shown in FIG.

First, in step S1, pixel data corresponding to the initial start position is calculated and scanning is performed at the current position.

Next, in step S2, the horizontal movement direction is determined in consideration of the view port boundary. At this time,

1) if the current scanning position is on the left boundary or the right boundary of the view port, and the scanning of the current line is not completed, horizontal movement is performed in the opposite traveling direction;

2) If the current scanning position is inside the viewport and the scanning of the current line is not completed, the horizontal movement is performed in the current progress direction. And,

1) the current scanning position is on the left boundary or the right boundary of the viewport, and the scanning of the current line is completed;

2) If the current scanning position is inside the viewport and completes scanning of the current line, vertical movement is performed (S3).

Therefore, in step S3, it is determined whether the next scanning position is outside the lower boundary of the viewport or below the last line to which the polygon belongs (S4), and if it is true, the scanning for the corresponding polygon is completed. It moves to a position (S5) and continues scanning.

The present invention has been described in detail with reference to preferred embodiments. However, one of ordinary skill in the art appreciates that various modifications can be made without departing from the spirit of the invention as set forth in the claims below.

Claims (9)

Performing far-near clipping on the far-near plane of the view-volume; Setting a polygon based on a horizontal and vertical coordinate boundary of the viewport in the one-far projected plane of the near-clipped view-volume and determining a scanning start point (x _i , y _i ) of the polygon ; Scanning vertices of the starting point and horizontal vertices to a horizontal boundary of the view port based on the determined starting point (x _i , y _i ); And Scanning vertices in the vertical direction and the starting point to a vertical boundary of the viewport based on the determined starting point (x _i , y _i ); View-volume clipping method comprising a. The method of claim 1, The polygon scanning starting point (x _i , y _i ) is: x _i = [x ₀ ], if 0 ≤ x ₀ <W _s = 0, if x ₀ <0 = W _s -1, if x ₀ ≥ W _s (Where n is an integer, [x] = n for all x where n ≤ x <n + 1 and W _s represents the horizontal width of the display screen's resolution), and y _i = [y ₀ ], if 0 ≤ y ₀ <H _s = 0, if y ₀ <0 = H _s -1, if y ₀ ≥ H _s View-volume clipping, where n is an integer, where [y] = n for all y where n ≦ x <n + 1 and H _s represents the vertical height of the display screen's resolution Way. The method according to claim 1 or 2, The scanning of the vertex in the horizontal direction and the starting point to the horizontal boundary of the view port with respect to the starting point (x _i , y _i ), A) horizontally moving in a direction opposite to the current scanning progress direction when the current scanning position is on the left boundary or the right boundary of the viewport and the scanning of the current line is not completed; B) when the current scanning position is inside the viewport and the scanning of the current line is not completed, performing horizontal movement in the current scanning progress direction View-volume clipping method comprising a. The method according to claim 1 or 2, The scanning of the vertices in the vertical direction and the starting point to the vertical boundary of the view port based on the determined starting point (x _i , y _i ), If the current scanning position is on the left boundary or the right boundary of the viewport, and the scanning of the current line is completed, or the current scanning position is inside the viewport and the scanning of the current line is completed, the vertical shift is performed. Steps to do View-volume clipping method comprising a. The method of claim 4, wherein The vertical movement may be performed by determining whether the next scanning position is out of the lower boundary of the viewport or below the last line to which the polygon belongs. If true, the scanning of the corresponding polygon is completed. Moving to continue scanning; view-volume clipping method. Clipping means for receiving a group of vertex data and performing far-near clipping with respect to a far-near plane of a view-volume; Means for viewport transforming a perspective-near-projected plane of the perspective-closed view-volume; Means for setting a polygon based on horizontal and vertical coordinate boundaries of the viewport and determining a polygon scanning start point (x _i , y _i ); And Means for determining a scanning progress direction in the horizontal or vertical direction of the viewport relative to the determined starting point (x _i , y _i ) and scanning the polygon vertices to a horizontal or vertical coordinate boundary of the viewport; View-volume clipping device comprising a. The method of claim 6, The polygon scanning starting point (x _i , y _i ) is: x _i = [x ₀ ], if 0 ≤ x ₀ <W _s = 0, if x ₀ <0 = W _s -1, if x ₀ ≥ W _s (Where n is an integer, [x] = n for all x where n ≦ x <n + 1 and W _s represents the horizontal width of the display screen's resolution), and y _i = [y ₀ ], if 0 ≤ y ₀ <H _s = 0, if y ₀ <0 = H _s -1, if y ₀ ≥ H _s View-volume clipping, where n is an integer, where [y] = n for all y where n ≦ x <n + 1 and H _s represents the vertical height of the display screen's resolution Device. The method according to claim 6 or 7, Said scanning means is: If the current scanning position is on the left boundary or the right boundary of the view port, and the scanning of the current line is not completed, horizontal movement is performed in a direction opposite to the current scanning progress direction, When the current scanning position is inside the viewport and the scanning of the current line is not completed, horizontal movement is performed in the current scanning progress direction. If the current scanning position is on the left boundary or the right boundary of the view port and the scanning of the current line is completed, or the current scanning position is inside the view port and the scanning of the current line is completed, the vertical movement is performed. To determine the scanning progress direction. The method of claim 6, Vertices input to the means for setting a polygon based on horizontal and vertical coordinate boundaries of the viewport and determining a polygon scanning start point (x _i , y _i ) include vertices that exist outside the view port. View-volume clipping device.