METHOD AND SYSTEM FOR SMOOTH-SCROLLING

Abstract: A display screen with a plurality of display lines contains a storage (34) that receives lateral offset values for each line to be displayed. When the corresponding line is to be displayed, the offset value is transferred from the storage (34) to an offset register (22), whose outputs control a multiplexer (26) to select an appropriately delayed output tap of a shift register, containing the signals to be displayed.

Description: The invention relates to a method and a system for smooth-scrolling or dotwise scrolling of a display screen which consists of a plurality of display lines, and more particularly to perform smooth-scrolling by each display line. As disclosed in Japanese Patent Laid-open Nos. 160984/83, 182690/83, 182691/83 and Japanese Patent Publication No. 36779/83, the smooth-scrolling of displayed image on a display screen has been attained by shift-controlling the displayed image dot by dot, which is to smooth-scroll the image of the entire display screen or the image of a display block. A similar prior art which is acknowledged in the preamble of present claims 1 and 3, is disclosed in EP-A-0 014 045. In this prior art, the scroll index latch is updated during the vertical blanking interval so that this single update in each vertical scan does not allow any different offset values for individual scan lines. This conventional smooth-scrolling technique for an image displayed on the display screen can not smooth-scroll the displayed image in each display line independently, selectively and dynamically. Therefore, it is not possible to realize a complicated and various image display for which the existence or nonexistence of smooth-scrolling or its speed is controlled for each display line. It is an object of the invention to provide a method for performing selective and dynamic smooth-scrolling of a displayed image in each display line independently, and a system therefore. This object is achieved by the invention of claims 1 and 3; embodiments of the invention are characterized in the dependent claims. The smooth-scrolling method according to the invention is constituted in such a manner that an offset value is set in a storage means, that, when an image is displayed for each display line, image information generated for each display line is shifted dotwise according to said offset value fetched from said storage means and then supplied to a display screen, and that said offset value for a display line to be smooth-scrolled is rewritten in synchronisation with the refreshing of said display screen. The method is characterised in that an offset value is set in the storage means for each display line. It is preferable that the rewriting of the offset value is attained in such a manner that, if the offset value exceeds a predetermined value, the offset value is set to zero and updated image information so as to shift the image by an amount one dot greater than the predetermined value is generated for the display line to be smooth-scrolled. The smooth-scrolling system according to the invention comprises a storage means for storing an offset value, a register means in which said offset value is loaded, a shifting means in which image information for each of the plurality of display lines is loaded and which shifts the image information dot by dot, and a selecting means for receiving the offset value from the register means and for selectively outputting the image information shifted in the shifting means according to the received offset value. The system is characterised in that the storage means includes an offset value for each display line of a display screen and that the register means is loaded at each occurrence of a display line. The shifting means may be realised by, for example, a shift register means. Also, the selecting means may be realised by, for example, a multiplexer means. Smooth-scrolling according to this invention can be performed for one display row as described in the embodiment; however, it is also possible to attain lateral smooth-scrolling in any screen configuration according to usage by controlling each display row with software. In addition, even if the display screen is constituted by a plurality of display areas, smooth-scrolling can be performed independently for each display row in each display area by providing a plurality of offset memories and offset registers. The invention allows to independently, selectively and dynamically smooth-scroll a display image in each display line. Thus, it is possible to realize complicated and various image display by controlling the existence or nonexistence of smooth-scrolling or its speed. An embodiment of the invention is now described in detail with reference to the drawings, in which: Figure 1 shows a block diagram of an embodiment of the invention; Figure 2 shows a diagram illustrating output data of the shift register; Figure 3 shows a diagram illustrating operation of an embodiment of the invention; and Figure 4 shows a diagram illustrating smooth-scrolling of a displayed image on a display screen. Figure 1 shows an embodiment of the method and the system for smooth-scrolling according to the invention. In the embodiment, the smooth-scrolling system is provided after a usual parallel-serial conversion means 10. It consists of a lateral offsetting means 20 provided with an offset register 22, a shift register 24 and a multiplexer 26, and a lateral offset memory 34 for storing an offset value for each display row. Parallel video signals PVS that are generated by a character generator or image buffer, not shown, are converted into serial video signals by the parallel-serial conversion means 10. The serial video signals are supplied to the shift register 24, and arranged to signals delayed by one dot clock by the shift register 24. The lateral offset memory 34 stores an offset value, which is written by software, determining how many dots each display row is laterally shifted. In displaying, the lateral offset memory 34 and the offset register 22 are controlled in such a manner that an offset value for a display row to be displayed is transferred to the offset register 22 during the flyback time of a display row just preceding to the display row to be displayed. Because of its functions, the lateral offset memory 34 may constitute a row information memory 30 together with a display start address memory 32 that stores a start address of each display row. The multiplexer 26 receives the offset value transferred to the offset register 22, selects and outputs serial video signals SVS shifted by the dot corresponding to the offset value. Figure 2 shows an example of it. The example shows how serial video signals of the sixth scanning line of characters A and B, respectively, are arranged to the offset values 0 to 7 inputted in the multiplexer 26. The characters A and B are displayed by using boxes consisting of 8 x 10 dots. Each dot patterns encircled by solid line at the top is at a display position at offset 0. The boundary of box is shown on the basis of the display position. The smooth-scrolling system with the above constitution allows to easily attain smooth-scrolling wherein the display image is laterally shifted by dot (dotwise) for each display row. In addition, it can be shown to the human eyes that the image moves smoothly to the lateral direction by varying the offset value and the display start address in synchronization with the refreshing of the display screen. Figure 3 shows an example of it. Also in this example, the character is displayed by using a box of 8 dots in the lateral direction. Now, n-th display row is referred. First, it is assumed that the display start address of the n-th display row is 1000, the offset value 0. In such case, the boundary of box for the character A coincides to the left end of display screen DL, so that displayed images "A, B, ..." in the n-th display row are displayed in a state with no lateral shifting (see Figure 4 (1)). Then, the offset value is set to 1 while maintaining the display start address at 1000. In such state, the multiplexer 26 in Figure 1 selects the connecting line 1. A video signal on this connecting line is advanced by one dot clock compared with that for offset value 0, so that the displayed image is shifted by one dot to the left on the display screen as shown in Figure 4 (2). Subsequently, the offset value is incremented one by one, and, when it reaches 7, the display start address is set to 1001 and the offset value to 0. The display screen becomes as shown in Figure 4 (9), which indicates smooth-scrolling by one character to the left. The timing to vary the value for offset is controlled by software according to feeling by the human eyes and amount of data.

Claims: A method for smooth-scrolling a displayed image on a display screen consisting of a plurality of display lines, the method comprising: setting an offset value in a storage means (34); shifting the image information generated for each display line dot by dot according to said offset value fetched from said storage means and then supplying said shifted image information to said display screen; and rewriting said offset value for a display line to be smooth-scrolled in synchronisation with refreshing of said display screen; characterised in that: an offset value is set in the storage means for each display line. The method of claim 1, wherein said rewriting of the offset value is attained in such a manner that, if said offset value exceeds a predetermined value, said offset value is set to zero and updated image information is generated, so as to shift the image by an amount one dot greater than said predetermined value, for said display line to be smooth-scrolled. A smooth-scrolling system for a display screen consisting of a plurality of display lines, the system comprising: storage means (34) for storing an offset value; a register means (22) in which said offset value is loaded; a shifting means (24) in which image information for each of the plurality of display lines is loaded and which shifts said image information dot by dot; and a selecting means (26) for receiving said offset value from said register means and for selectively outputting said image information shifted in said shifting means according to said received offset value; characterised in that the storage means (34) includes an offset value for each display line of a display screen; and the register means (22) is loaded at each occurrence of a display line. The system of claim 3, wherein said shifting means is a shift register (24). The system of claim 3 or 4, wherein said selecting means is a multiplexer (26). The system of one of the claims 3 to 5, wherein a display start address memory (32) is provided.

Inventors: AOKI, TAKAAKI, IIDA, HIROYASU, NOJIMA, KATSUYUKI
Applicants: INTERNATIONAL BUSINESS MACHINES CORPORATION
Application year: 1986
Main classification: G09G1
IPC codes: G09G5