JPH01154294A - Polygon drawing system - Google Patents

Abstract

PURPOSE:To make a polygon being free from an unnecessary line by suppressing unnecessary edge generated at the time of generating plural polygons by clipping process. CONSTITUTION:With regard to each of the respective apexes of plural polygons obtained by clipping, whether an intersection with each borderline of a clip frame exists of not is described by a boundary code Cp, and based on this boundary code Cp, a boundary code C of the intersection of each side of plural polygons and a scan line, and a boundary code Cs between each adjacent intersection on the scan line are derived successively, and when all bit codes in this obtained boundary code Cs are a code '0', a vector for face painting is generated between the intersections corresponding to its boundary code Cs. On the other hand, when a code '1' exists in a bit train of said boundary code Cs, the generation of a vector required for face painting is suppressed between the intersections corresponding to its boundary code Cs.

Description

[Detailed Description of the Invention] [Summary] Regarding a polygon drawing method that uses clipping processing and surface painting processing, the present invention aims to suppress the drawing of pseudo-image edges that occur when multiple polygons are generated by clipping processing. For each vertex of a plurality of polygons generated by clipping, determine whether or not that vertex intersects each boundary line of the clipping frame with a number of bits equal to the total number of boundaries of the clipping frame. And each bit is described by a boundary code consisting of a bit string in one-to-one correspondence with each boundary line of the clip frame, and each intersection of each side of the plurality of polygons and the scan line is Find the boundary code of each intersection by performing a logical AND operation for each corresponding bit between the boundary codes of the vertices at both ends of the edge, and calculate the correspondence of the boundary codes between adjacent intersections on the scan line. The boundary code between each intersection point is obtained by performing a logical AND operation for each bit, and the generation of a vector for filling in the area between the intersection points is controlled based on the code state of the obtained boundary code.

[Industrial application field]

This invention relates to a polygon drawing method in a drawing method that uses clipping processing and surface painting processing.

[Conventional technology]

Figure 4 shows a conventional polygon drawing method that uses clipping processing and fill processing. A polygon 3 as shown in the figure (b) is generated by clipping using a rectangular clipping frame 2, and then a vector 4 for filling the inside of the generated polygon 3 is generated by area painting processing. By performing rask scanning according to this vector sequence, a polygon 3 whose interior is painted as shown in FIG. 2C is displayed on a CRT display or the like.

[Problem that the invention seeks to solve]

When using the conventional drawing method described above, when a polygon to be processed 1 having sides A, B, and C as shown in FIG. 5(a) is clipped with a clip frame 2 to generate a plurality of polygons, As a result of this clipping, three polygons 5, 6.7 as shown in FIG. .

Conventionally, a horizontal pseudo edge parallel to the scan line 9
There was a way to suppress this when drawing, but
There is no means for suppressing the pseudo edges 8 in the direction perpendicular to or intersecting the scan line, and there is a problem in that the pseudo edges 9 are drawn as they are on the screen after the surface painting process, as shown in FIG. 3(C).

An object of the present invention is to suppress the drawing of pseudo edges that occur when a plurality of polygons are generated by clipping processing.

[Means for solving the problem] As shown in the processing flowchart in Figure 1, a plurality of polygons are generated by clipping the figure data of the polygon to be processed with a clip frame, and In a polygon drawing method in which the interior of the polygon is drawn by filling the inside of the polygon with fill processing, for each of the vertices of the plurality of polygons generated by the above clipping, the border between that vertex and the above clipping frame is The presence or absence of intersection with a line is described by a boundary code C2 consisting of a bit string having a number of bits equal to the total number of boundaries of the clip frame and each bit corresponding to each boundary line of the clip frame on a one-to-one basis, For each intersection between each side of the plurality of polygons and the scan line, a logical AND operation is performed for each corresponding bit between the boundary codes C9 of the vertices at both ends of the sides where the intersections intersect. Find the boundary code co of the intersection, and perform an AND operation for each corresponding bit of the boundary code Cc between adjacent intersections on the scan line to find the boundary code Cs between each intersection. The generation of a vector for filling in between the intersection points is controlled by the code state of the boundary code C8.

[For production]

For each vertex of a plurality of polygons obtained by clipping, the presence or absence of intersection with each boundary line of the clip frame is described by a boundary code C9, and based on this boundary code C2, each side of a plurality of polygons and The boundary code C at the intersection with the scan line and the boundary code C5 between adjacent intersections on the scan line are sequentially obtained, and when all bits in the obtained boundary code Cs are code 0°, generates a vector for filling between the intersection points corresponding to the boundary code Cs.

On the other hand, in the bit string of the boundary code Cs, the code "1°'"
If there is, the generation of vectors for surface painting is suppressed between the intersections corresponding to the boundary code C3.

Therefore, generation of vectors for fill-in is suppressed in the pseudo edge portion generated by clipping, and pseudo edges are no longer drawn on the screen.

〔Example〕

FIG. 2 shows an embodiment of a drawing device configured according to the present invention, in which a segment management unit 21 sends and receives graphic data such as polygons to be processed and necessary information to and from a host computer, and segments The segment buffer 22 is a circuit that manages the buffer 22. The segment buffer 22 is a memory that holds and stores graphic data sent from the host computer and its attribute data.The coordinate conversion unit 23 converts data based on the coordinate conversion matrix sent from the segment management unit 21. The clipping processing unit 24, which is a circuit that converts the coordinates of graphic data from the world coordinate system to the screen coordinate system, converts the polygon 1 to be processed given as graphic data as shown in FIG. Circuit clipping at position,
The fill processing unit 25 is a circuit that generates a vector sequence for filling the inside of a polygon generated by clipping processing, and the circuit 26 is a circuit for drawing the vector sequence sent from the fill processing unit 25 by rask scanning. The frame buffer 27 is a memory that temporarily stores the dot pattern data to be displayed on the CRT display 28.

FIG. 3 shows an example of drawing according to the above embodiment, in which a polygon l having the same shape as shown in FIG. This is shown as an example.

The segment management section 21 reads the graphic data sent from the host computer from the segment buffer 22 and sends it to the coordinate conversion section 23, which converts the coordinates of this graphic data from the world coordinate system to the screen coordinate system and performs clipping. It is sent to the processing section 24.

The clipping processing unit 24 converts the processed polygon 1 shown in FIG. 3(a) given by the graphic data into a clip frame 2.
Clip at the positions of sides A, B, and C using Figure 3 (
Generate the three polygons 5.6.7 shown in b).

The clipping processing unit 24 consists of four bits B, ~B4 equal to the number of the four boundary lines Boundary codes C--(Bl, BZ, B3°B,) are prepared in advance in a one-to-one correspondence with each other, and the three polygons 5 and 6 generated as described above are
．． The above boundary code C is applied to each of the vertices P1 to P of 7.
Give P.

Then, the clipping processing unit 24
For each of = P 9, it is determined whether or not the vertex intersects with which border line X1-x4 of the clip frame 2, and the crossing state is determined using the above border code C, = (B,,B
,,B,,B,).

That is, as shown in FIG. 3(a), since the vertex P1 does not intersect with any of the boundary lines XI-Xa of the clip frame 2, the peak corresponding to the boundary line X+ in the boundary code C2 is "'0", which corresponds to the boundary line X2)Bz=
“0” B corresponding to boundary line X3 = “O”, bit Ba = “°0” corresponding to boundary line Become.

Also, since the vertex P2 intersects only the boundary line X3 of the clip frame 2, only the bit B3 corresponding to this boundary line , its boundary code CP is (0,0°1.0).

Similarly, for each vertex P3 to P, the bit corresponding to the boundary line that intersects with that vertex is set to "l", and the bit corresponding to the boundary line that does not intersect is set to i' foot "'0", and all The vertex P of

The boundary code CI for ~P9 is determined.

The boundary code cp of each vertex P, -P of the plurality of polygons 5, 6°7 thus obtained is as follows.

Boundary of P:] −toC,= (0,0,0,0>P2
(7) Boundary near-1”Cp= (0,0,1,0)P3
boundary code CP = (0,0,1,0') boundary code C of P4, = (0,1,0,0) boundary code C of P5
P= (0,1,0,0) P6 boundary code Cp= (
0,0,0,O) P7 boundary code Cp= (0,1,
0,0) P8 boundary code C,= (0,1,1,0)
Boundary of P] (Cp=(0,0,t,0) The above boundary code C2 is sent to the fill processing section 25 along with the graphic data for polygons 5, 6.7,
Next, perform the processing described below to generate a vector sequence for surface painting.

First, as shown in Figure 3 (C), scan lines for surface painting! and the intersections a and b with each polygon 5, 6.7
, c, and d, a logical product (AND) operation is performed for each corresponding bit between the boundary codes C9 of the two vertices at both ends of the polygon side where the intersection points intersect, and each intersection point a, b ,c.

Find the boundary code C0 of d. Note that the intersection C in the same figure (C) is the intersection of the scan line 2 and the side connecting the vertices P4 and P, and the intersection d is the intersection of the scan line 1 and the side connecting the vertices P7 and PI1, It is assumed that these two intersection points C and d overlap.

Since the intersection a intersects the side connecting the vertices P and P of polygon 5, the boundary code C,= (0,0,0,0) of the vertex P located at both ends of this side and the vertex P9 The boundary code C, = (0, 0, 1, 0) of the intersection point a is calculated by performing an AND operation for each corresponding bit.
Find = (0, 0, 0, 0).

Similarly, the boundary code CP between vertices P+ and P2 is used for the intersection point , the boundary code CI between the vertices P4 and P5 is used for the intersection point C, and the boundary code CI is used for the intersection point d.

Using the boundary code C2 of and Pll, find the intersection point of each
Find the boundary code C6 of c and d.

The boundary code Cc of each intersection point a%d thus obtained is as follows.

Boundary code of intersection a Cc = (0,0,0,0) Boundary code of intersection Cc = (0,O,O,O) Boundary code of intersection C Cc = (0,1,O,O) Intersection d Boundary code C, = (0,1,0,0) Next, the surface painting processing unit 25 scans the scan line! based on the boundary code Cc of the intersection a-yd. An AND operation is performed for each corresponding bit of the boundary code C6 between the adjacent intersections a and b, and the intersections C and d, to obtain a boundary code C8 between the intersections as shown below.

Boundary between intersection (a-b): 2-)' Cs = (0,0
,0,0) Boundary code C,=(0,0) between the intersection (c-d)
1, 0, 0) Then, the filling processing unit 25 examines the sign state of each bit in each of the obtained boundary codes C3, and determines that all bits in the boundary code Cs are “0”. For the intersections (a-b) where
d) Suppress the generation of vectors for filling the space between spaces.

The surface painting processing unit 25 executes the above-mentioned processing for all scan lines on the screen, obtains vectors 4 for surface painting between all intersection points, and sends the obtained vector sequence to the DDA 26.

The DDA 26 develops the vector sequence sent from the surface painting processing unit 25 into a dot pattern, stores the obtained dot pattern data in the frame buffer 27, and outputs the data to the CRT.
The display 28 uses this dot pattern data to display the polygons 5, 6, and 7 by rask scanning.

As a result, only the three polygons 5, 6, and 7 are drawn on the screen of the CRT display 28 as shown in FIG. )
will no longer be drawn.

In addition, if you want to display the outer periphery of the polygon as a border in a different color from the inside, set the boundary code 09 of the vertices located at both ends of each side of the polygon 5, 6゜7 for each focus. It is sufficient to perform a logical product operation and draw an outer peripheral line only for the side where all bits in the obtained code are "0". As a result, vertices P1-P2, P3-Pa, Ps-P
6.P6~P? , P9 to P3 are displayed with an outline.

Although the above embodiment has been explained using a two-dimensional figure as an example, the present invention can be extended to a three-dimensional figure, and in the case of drawing a three-dimensional figure, the clip frame for clipping described above is It is formed by surfaces rather than line segments. Therefore, the concept of the term "boundary line" in the present invention naturally includes both a boundary line and a boundary surface.

Furthermore, although the above embodiment has been described with reference to the case where the most -i rectangular frame is used as the clip frame 2, it goes without saying that the clip frame 2 is not limited to the rectangular frame and any polygonal frame can be used.

〔Effect of the invention〕

According to the present invention, it is possible to suppress the drawing of pseudo edges that occur when a plurality of polygons are generated by clipping processing, and it is possible to suppress the drawing of pseudo edges during filling processing, and it is possible to obtain the special effect of being able to draw polygonal figures without unnecessary lines. can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the principle of processing of the present invention, FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 3 is a diagram showing an example of drawing according to the present invention, FIG. 4 is an explanatory diagram of the conventional method, 'FIG. 5 is an explanatory diagram of the problems of the conventional method. 1...Polygon to be processed, 2...Clip frame, 5-6.
...Polygon, X l"
Boundary code of intersection of scan line and polygon side, C3
...Boundary code between intersection points,! ...This is a scan line.

Claims (1)

[Claims] A polygon drawing method in which multiple polygons are generated by clipping the graphic data of the polygon to be processed with a clip frame, and the interior of the multiple polygons is drawn by filling the inside of the multiple polygons with fill processing. , for each of the vertices of the plurality of polygons generated by the clipping, the presence or absence of intersection between the vertex and each border line of the clip frame is determined using a number of bits equal to the total number of borders of the clip frame. and set each bit to 1 on each border of the clipping frame.
Boundary code (C_p
), and for each intersection between each side of the plurality of polygons and the scan line, logic is written for each corresponding bit between the boundary code (C_p) of the vertices at both ends of the side where the intersection intersects. The boundary code (C_c) of each intersection is obtained by performing a product operation, and the boundary code (C_c) between each intersection is calculated by performing an AND operation for each corresponding bit of the boundary code (C_c) between adjacent intersections on the scan line. A polygon drawing method characterized in that the boundary code (C_s) of the boundary code (C_s) obtained is determined, and the generation of a vector for filling in between the intersection points is controlled based on the code state of the obtained boundary code (C_s).