Method for scrolling images on a screen

Abstract: A screen is divided into plural character positions each having an equal area. In at least one of the character areas, characters (1-4, Fig.11) having position shifted patterns are displayed sequentially, so that a displayed pattern (100) is scrolled in a predetermined direction.

Description: This invention relates to a method for scrolling images on a screen, and, more particularly, to a method for displaying images to be scrolled to provide viewers with a sense of depth. In a conventional method for displaying images on a screen by use of a computer, the images are displayed by applying shadow to articles or by using the perspective representation method, so that pictures having depth are generated on the screen to provide viewers with cubic sense. In a computer having a memory of a sufficient capacity, a number of image frames can be defined in a VRAM of the memory, so that images having depths specified to each image frame are stored and are superimposed on the screen. In this method, when moving images are displayed on the screen, cubic sense is increased by moving articles near viewers at a slow speed and articles far from viewers at a fast speed. In a computer such as a home TV game machine having a memory of a small capacity which is low in cost, however, it is difficult to prepare a number of image frames having various depths. Such a computer has a CPU with a slow operation speed. Consequently, it is difficult for motion pictures to provide images having a perception of depth. Accordingly, it is an object of the invention to provide a method for scrolling images on a screen, in which a smooth scroll of images is realised by the character units. It is another object of the invention to provide a method for scrolling images on a screen, in which an artificial multi-scroll of images is realised even using a memory of a small capacity. According to the present invention as specified in claim 1, there is provided a method for scrolling images on a screen, each image having a plurality of image portions to be displayed at predetermined positions relative to one another, each of the image portions having a predetermined size in dots on the screen, the image contents of each image portion to be displayed being represented by a character code stored at a memory location determined by said relative position, and by the contents of a character generation memory whose location is determined by the value of said character code, the method comprising the step of: displaying sequentially at a screen position image portions whose image contents are displaced from one displayed portion to the next in a desired direction thereby achieving the effect of scrolling one or more of the image portions of the respective image in the desired direction. The invention will be explained in more detail in conjunction with the accompanying drawings, wherein: Fig. 1 is a diagram explaining a display screen; Fig. 2 is a diagram showing a virtual screen having addresses of characters in a background attribute table (BAT); Fig. 3 is a diagram showing a position and a content of the BAT in a VRAM; Fig. 4 is a diagram showing the BAT; Fig. 5 is a diagram showing a position and a content of a character generator (CG) in the VRAM; Figs. 6 to 9 are diagrams explaining a display control of a background; Figs. 10A and 10B are diagrams explaining a video output of the background; Figs. 11A to 11D are diagrams showing square character patterns in a method for scrolling images on a screen, in which a vertical scroll is realised, in a preferred embodiment according to the invention; Figs. 12A to 12D are explanatory diagrams showing square character patters in a method for scrolling images on a screen, in which an inclination scroll is realised, in the preferred embodiment; Figs. 13A and 13B are plan and side views explaining displays of a valley in the preferred embodiment; and, Figs. 14A and 14B are diagrams explaining superimposing of a smooth scroll and an artificial multi-scroll in the preferred embodiment. Before explaining a method for scrolling images on a screen of the preferred embodiment according to the invention, the aforementioned background of the invention will be explained again. In a computer system which is used in the invention, two kinds of image frames defined "background" and "sprite" are combined to provide one image frame, wherein the background image frame is composed of patterns defined "character". In the following explanation, a character is composed of 8 x 8 dots as one unit. Fig. 1 shows a display screen which is defined by values set in registers, in which the horizontal set values are defined by the number of characters, and the vertical set values are defined by the number of rasters. The registers are for HSW (horizontal sync pulse width) HDS (horizontal display start position), HDW (horizontal display width ), HDE (horizontal display end position), VSW (vertical sync pulse width), VCR (vertical display end position), VDW (vertical display period), and VDS (vertical display start position). Fig. 2 shows a virtual screen which is composed of 32 x 32 characters, to which addresses 0, 1, 2...are assigned. Fig. 3 shows a background attribute table (BAT) having a capacity equal to the addresses of the virtual screen which is a portion of a VRAM. The BAT stores, at addresses corresponding to each address of the virtual screen, a set of a character code and a CG colour, as explained next. Fig. 4 shows the set of the character codes (12 bits) for defining a pattern on a character, and the CG (4 bits) for defining a colour. Fig. 5 shows a character generator (CG) region which is also a portion of the VRAM. The CG region is composed of CGS each having four facets CH0, CH1, CH2 and CH3 designated in a group by the character code of the BAT. The first and second facets CH0 and CH1 provide the first 8 words CG0, and the third and fourth facets CH2 and CH3 provide the second 8 words CGl as shown therein. As shown, each of the four facets CH0 to CH3 is composed of 8 x 8 dots and is designated to provide one bit in order from 64 bits, so that a four bit signal is obtained to be combined with the four bit CG colour, thereby providing an address signal of 8 bits for a memory called "a colour pallet". The display control of the background is carried out in a horizontal display period, as explained below by use of Figs. 6 to 10A and 10B. In Fig. 6, a position of a raster is detected in an address unit 10 to generate an address signal on the virtual screen as shown in Fig. 2, by which the BAT 21 of the VRAM 20 is accessed to provide a character code and a CG colour as shown in Fig.4. The character code is supplied to the address unit 10 to generate an address signal for accessing the CG region 22 of the VRAM 20, and the CG colour is supplied to be stored in a CG colour shift register 31 of a background shift register 30. In Fig. 7, the CG region 22 is accessed by the address unit 10, so that the first two facets CH0 and CHl are supplied to be stored in first and second shift registers 32 and 33 of the background shift register 30. In Fig. 8, the second two facets CH2 and CH3 are read from the same address of the CG region 22 to be stored in third and fourth registers 34 and 35 of the background shift register 30. In Fig. 9, the four bit CG colour is supplied from the CG colour shift register 31, and one bit is supplied from each of the shift registers 32 to 35 to provide a four bit signal, so that an eight bit address signal VD0 to VD7 is generated to be supplied through a priority circuit 40 to a colour pallet (not shown). Fig.10A shows the eight bit address signal VD0 to VD7, to which a bit VD8 is combined, wherein the background is displayed by VD8 being "0", and a sprite is displayed by VD8 being "1". Fig.10B shows a display output during a period of retrace, in which the bit VD8 is "1", and the bits VD0 to VD7 are "0". For the display of sprites, a sprite shift register 50 is used to store sprite data. In a display as described above, vertical and horizontal smooth scrolls are carried out by use of registers called BGY and BGX scroll registers, in which scroll data are stored. The vertical scroll can be performed by a unit of rasters, and the horizontal scroll can be performed by a unit of dots. In the vertical scroll based on the unit of rasters, a scroll cannot be carried out character by character. On the other hand, a horizontal scroll can be done character by character, because the horizontal scroll is carried out dot by dot. In this case, however, a method of raster interruption must be adopted. As a result, the setting of timing becomes difficult. This is one of the disadvantages that is overcome by the present invention. Next, a method for scrolling images on a screen of the preferred embodiment according to the invention will be explained in Figs. 11A to 11D. Fig. 11A shows a character pattern No. 1 of 8 x 8 dots having a closed square belt shape 100 (referred to as "mark" hereinafter), and Figs. 11B to 11D show character patterns No. 2 to No. 4 of the same size having marks 100, each position of which is shifted in the vertical direction by two dots. In operation, the character patterns No. 1 to No. 4 are, in order, displayed at an addressed position(s) selected from the addresses 0, 1, 2, ... of the virtual screen (Fig. 2) in accordance with the process using the BAT 21 and the CG region 22 of the VRAM 20, the background shift register 30, the colour pallet, etc. as explained before, so that the vertically scrolling display of the mark is carried out at the selected address position on the screen, wherein the mark moves downwardly. On the other hand, the mark moves in the upper direction when the character patterns are displayed in the order of No. 4 to No. 1. This scroll is carried out by a program stored in a ROM (not shown), and is defined as "artificial scroll" which is discriminated from a smooth scroll which is carried out by a system (hardware). The smooth scroll must be carried out on a whole plane of the screen, while the artificial scroll can be carried out on a limited portion of the screen and on different portions thereof by using character patterns having different marks. The artificial scroll using different marks is defined as "artificial multiple scroll", in which scrolls may be carried out in any direction such as vertical, horizontal, and at an inclination by using character patterns having predetermined shifted marks. In realising an inclination scroll by using the smooth scroll, vertical and horizontal scrolls must be combined. However, this can be carried directly by using the artificial multiple scroll of the invention. Figs. 12A to 12D shows character patterns No. 1 to No. 4 of 8 x 8 dots having marks 100, on which the inclination scroll can be carried out. The mark moves in the upper left to lower right direction by displaying the character patterns in the order of No. 1 to No. 4, while the marks moves in the lower right to upper left direction by displaying them in the order of No. 4 to No. 1. Figs. 13A and 13B shows a display of a valley 200 of V shape having stones 210A on the bottom and 210B and 210C on the outside. In order to provide viewers with cubic sense on this display, the bottom stones 210A are controlled to move slowly as compared to the outside stones 210B and 210C, if it is assumed that the viewer is looking down the valley 200 from an airplane. In addition, the stones 210A are preferably displayed to be smaller than the outside stones 210B and 210C. Fig. 14A shows the bottom and outside stones 210A, 210A', 210B, 210B' and 210C displayed on a right half portion of the screen having a dotted line A or an original position in accordance with the method as explained in Figs. 13A and 13B. As can be understood from the illustration in Fig. 14A, the bottom stone 210A occupies one character (8 x 8 dots), and the stones 210A', 210B, 210B' and 210C occupy 4 characters, 9 characters, 16 characters, and 36 characters respectively in terms of area. That is, the stones 210A to 210C occupy 16 characters in the horizontal direction on the right half portion of the screen. In the vertical direction, a predetermined number of the bottom stones 210A are arranged to contact with upper and lower ones. Other stones 210A' to 210C are arranged in the vertical direction in the same manner as the stones 210A. In this assumption, the vertical smooth scroll is carried out in the lower direction in accordance with a rate of 6 dots during a period of lV which is a unit of the detection number in a vertical retrace period. In this preferred embodiment, the period of lV is 1/60 sec. In addition to the vertical smooth scroll, the artificial multiple scroll is applied to the display of the valley in accordance with the invention. That is, four dots artificial vertical scroll is carried out for the bottom stones 210A, three dot artificial vertical scroll for the stones 210A', two dot artificial vertical scroll for the stones 210B, one dot artificial vertical scroll for the stones 210B', and no artificial vertical scroll for the stones 210C, respectively, in the upward direction, as shown in Fig. 14A by arrows. The resultant scroll values obtained shown in the table below. STONES SMOOTH SCROLL ARTIFICIAL SCROLL RESULTANT SCROLL 210A +6 -4 +2 210A' +6 -3 +3 210B +6 -2 +4 210B' +6 -1 +5 210C +6 0 +6 In accordance with the resultant vertical scroll, the stones 210A to 210C move downwardly by dots as shown in Fig. 14B, after a time period 3V(=3/60 sec). In Fig. 14, the dot amounts are indicated by three times the resultant scroll values. Consequently, the display of the valley provides viewers with cubic sense, the images having depth and power. In accordance with a smooth scroll conducted by a system, operation is required to comply with the algorithm of the system. On the other hand, an artificial multiple scroll of the invention is carried out by a user program, so that flexibility is obtained in operation. As explained above, a vertical scroll can be carried out character by character. This has significance when used in combination with the vertical smooth scroll which is carried out raster by raster. Consequently, there is a significant advantage when providing motion pictures having depth. In an ordinary display of a background, few characters are used in order to decrease the required memory capacity. The artificial multiple scroll of the invention complies with the requirements of the limited memory capacity of a home TV game system.

Claims: A method for scrolling (1-4) images on a screen, each image having a plurality of image portions to be displayed at predetermined positions relative to one another, each of the image portions having a predetermined size in dots on the screen, the image contents of each image portion to be displayed being represented by a character code stored at a memory location determined by said relative position, and by the contents of a character generation memory whose location is determined by the value of said character code, the method comprising the step of: displaying sequentially at a screen position image portions whose image contents are displaced from one displayed portion to the next in a desired direction thereby achieving the effect of scrolling one or more of the image portions of the respective image in the desired direction. The method for scrolling images on a screen according to claim 1, wherein: said character generation memory is a VRAM, and has a background attribute table (21) for storing the address of said memory location; and said image portion is displayed in colours designated in a colour pallet by said contents of said VRAM. The method for scrolling images on a screen according to claim 1 or claim 2, wherein: each image portion is represented by at least two image patterns which are displayed to have small and large sizes in accordance with a perspective representation.

Inventors: AOYAMA KOJI, AOYAMA, KOJI, Aoyama, Koji, c/o Hudson Soft Co. Ltd.
Applicants: HUDSON SOFT CO LTD, HUDSON SOFT CO., LTD.
Application year: 1992
Main classification: G06T15
IPC codes: G06F3, G06T15, G09G5