Display control apparatus

Abstract: A display control apparatus is composed of display device driver means for writing image information into a frame buffer, and display scanning means for sequentially displaying the image data stored in the frame buffer for each line of the display. The display control apparatus further is composed of partially rewritten line determination means for obtaining from the display device driver means information regarding lines to be written into the frame buffer, and generating in accordance therewith the lines for which the display is to be scanned, and display scan line control means for obtaining from the partially rewritten line determination means lines to be scanned to specify such lines for the display scanning means.

Description: The present invention relates to a raster scan display control apparatus. More particularly, the invention relates to a display control apparatus for controlling a display device, a system including the display control apparatus and the display device, and a host system therefor. Hitherto, in a raster scanning display control apparatus, the structure has been arranged to sequentially display image information accumulated in a frame buffer per line while keeping constant the displaying cycle for each of the scanning lines and the displaying cycle for one frame as well. Furthermore, if the frame frequency cannot be made high due to the material properties or electrical restraints of a display device, so-called interlace method is adopted to prevent flickers (screen flickering). In a display device using a ferroelectric liquid crystal, particularly in case of a device having many numbers of lines, the use of a high order interlace (multi-interlacing) is imperative in order to prevent flickers. However, if a display is performed by the use of the multi-interlacing, the object which is reproduced on a screen (for example, cursor, characters, icon, other graphics, or the like) is accompanied by dispersion when it is shifted or newly reproduced; hence spoiling the quality of display significantly. Particularly, a mouse cursor is directly operated by the user and its operational frequency is also high. Therefore, the dispersion attributable to the use of the mouse cursor may spoil the operational sensitivity of the entire system. As a means to prevent the dispersion of an object on a screen when multi-interlacing is applied, there is a method called "partial rewriting" such as proposed by Kanbe et al. (U.S. Patent No. 4,655,561). This method is such that in shifting an object on a screen or reproducing it thereon, only the line area where the screen representation changes is temporarily displayed by non-interlacing. There is also a method to implement this partial rewriting by means of software such as proposed by Inoue et al. (e.g. U.S. Patents US-A-5,058,994 and US-A-5,091,723). EP-A-0368117 discloses display control apparatus in which lines of an image that are to be rewritten, in a partially rewriting mode of operation, are determined by comparing incoming data with corresponding data stored in a buffer memory. It is in this case necessary to perform operations of accessing data in memory, operations which require significant processing time and thus delay since this is in addition to the time required for updating the buffer memory and accessing data in the memory for display writing. Particular mention also is made of EP-A-0416172 which discloses a control apparatus having the features set out in the preamble of claim 1 appended. As described therein, a graphic controller generates graphic image data in response to drawing instructions received from a host system, and stores this data in a video random access memory (a frame buffer). At the same time, the graphic controller stores line address and remaining line count data in a register for use in controlling switching between the refresh and partially rewriting modes of displaying an image on a FLCD. The present invention, as defined in the appended claims, is intended as a solution to the problem of dispersion mentioned above. In the accompanying drawings: Fig. 1 is a functional block diagram to illustrate a fundamental structure of an information display apparatus according to an embodiment of the present invention; Fig. 2 is a view showing the arrangement of hardware of the embodiment of figure 1; and Fig. 3 is a view showing an implementation of the respective functional blocks shown in Fig. 1 in conjunction with the arrangement of the hardware shown in Fig. 2. Hereinafter, a detailed description will be given of an embodiment of the present invention, referring to the accompanying drawings. Fig. 1 is a view showing a fundamental structure of a display control apparatus embodying the present invention. In Fig. 1, display driver means 12 up-dates image data in a frame buffer 13 as requested by application software 11 and at the same time, transfers information regarding up-dated lines to partially rewritten line determination means 16. The partially rewritten line determination means 16 determines the lines for which partial rewriting must be executed on the basis of the information transferred from the display driver means 12, and then delivers information to scan line control means 17. The scan line control means 17 specifies the scanning line transferred from the partially rewritten line determination means 16 for variable scan position raster scan display means 14. The variable scan position raster scan display means 14 transfers the data in the frame buffer corresponding to the line specified by the scan line control means 17 to an FLC display 15 for display. This variable scan position raster scan display means 14 transfers data corresponding to each line sequentially to the FLC display 15 for display from the image data in the frame buffer 13 in accordance with a given regulation unless any line to be scanned is specified by the scan line control means 17. Now, Fig. 2 will be explained. Fig. 2 is a view showing an example of hardware to implement the partially rewritten line determination means 16 and scan line control means 17 shown in fig. 1 by means of software. A central arithmetic processing unit (CPU) 21 executes operational system software and application software instructions. An SBus controller 22 (SBus - esbus - is a registered trade mark of Sun Microsystems Inc.) changes appropriately the addresses generated by the central arithmetic processing unit 21 to enable access to various peripheral devices. A main memory 23 holds instruction codes and data for and from the operational system, application software, or the like currently under execution. A hard disk 24 stores the software and data as files. A keyboard 25 receives inputs from a system operator. A frame buffer 13 stores image data. A graphic controller 27 has functions to allow the image data stored in the frame buffer 13 to be displayed on the FLC display 15 (hereinafter referred to as FLCD). The graphic controller 27 also has a function for the execution of instruction codes held in a local memory 28. The local memory 28 holds the instruction codes and data to be executed by the graphic controller 27. Of those mentioned above, the central arithmetic processing unit 21, SBus controller 22, main memory 23, hard disk 24 and key board 25 constitute a host system 34 (fig. 3) while the frame buffer 13, FLCD 15, graphic controller 27, and local memory 28 constitute graphic sub-system control module 37 (Fig.3). The graphic sub-system 37 is connected to the host system 34 through the SBus 26. Each means 12, 16, 17 and 14 shown in Fig. 1 can be implemented as software executable on the hardware shown in Fig. 2. In Fig. 3, an X client 30 (X or X Window System is a trade mark registered by Massachusetts Institute of Technology) executes application software 11 while an X server 31 issues image representation requests. The X server 31 functions in response to the display driver means 12 to write image data into the frame buffer 13 using the functions of a graphic device driver 33. Likewise, a partial rewriting library 32 functions in response to the partially rewritten line determination means 16 and remote firmware 35, and to the scan line control means 17. The partial rewriting library 32 obtains information regarding the image representation area (i.e. the area that is to be rewritten) from the X server 31 to determine the lines to which partial writing should be applied and transfers such information to the remote firmware 35 using the function of the graphic device driver 33. The remote firmware 35 specifies the scanning line for the display controller 36 on the basis of this information. The X client 30, X server 31, partial rewriting library 32, and graphic driver 33 are the softwares executed by the central arithmetic processing unit 21 in fig. 2. On the other hand, the remote firmware 35 is a software executed by the graphic controller 27. The display controller 36 can be implemented with the functions provided by the graphic controller 27 as hardware. As a graphic controller provided with such a function as this, TMS34020 (Registered Trade Mark: Texas Instruments Inc.) or the like can be named, for example. In the present invention, as represented by the embodiment shown in Fig. 3, both means 16, 17 may be realised by one software module. As described above, a process routine for determining a partial rewriting line is incorporated in a process routine with which to write into the frame buffer, and then further with this routine, the display scanning lines are actually controlled. Also, with the above-mentioned structure, when an object to be represented on a display is generated or shifted, the display device driver means can rewrite only the image information in a portion in the frame buffer, which is changed due to the generation or shifting of such an object. The partially rewritten line determination means can also generate the lines for which the display should be scanned on the basis of the information regarding the lines to be written into the frame buffer, which is obtained from display device driver means. Also, the display scan line control means can obtain the scanning line from the partially rewritten line determination means to specify such lines for the display scanning means. The display scanning means reads the image information of the scanning line from the frame buffer in accordance with the instruction from the display scan line control means so as to enable rewriting of the corresponding scanning line on the display. In this way, only the scanning lines including the image information which has been changed due to the generation or shifting of an object can be scanned, so that the object can be generated or shifted substantially on real time on the display. Further details of the X or X Window System referred to herein, are described in Volume One of Xlib Programming Manual for Version II of the X Window System, by Adrian Nye, published by O'Reilly & Associates Inc. The foregoing disclosure should be interpreted as illustrative only and not to be interpreted in a limiting sense. The present invention is limited only by the scope of the following claims.

Claims: A raster scan display control apparatus for controlling the writing and rewriting of an image on a display device, said apparatus comprising: a host system (34) having: a central arithmetic processing unit (21); a main memory (23) to store currently executable instruction codes, and data for current use, respectively, for execution and use by said control arithmetic processing unit (21); a programme and data memory (24) containing programme instruction codes and data, transferable to said main memory (23) for current execution and use; and a bus controller (22) to control transfer of information and image data to and from said host system (34); a graphic subsystem (37) having: a graphic controller (27); a local memory (28) containing executable instruction codes and data for execution and use by said graphic controller (27); and a frame buffer (13) to store up-datable image data that is to be updated and transferred to the display device (15), and which represents an image to be displayed by the display device (15); and a bus (26) for transferring information between said host system (34) and said graphic controller (27) and for transferring image data from said host system (34) to said frame buffer (13), wherein said local memory (28) contains first instruction codes (36) executable by said graphic controller (27) to transfer image data stored in said frame buffer (13) to the display device (15), and second instruction codes (35) to specify each line of an image, displayed by the display device (15), which is to be rewritten using image data transferred from said frame buffer (13); which apparatus is characterised in that: said programme memory (24) of said host system (34) contains: third instruction codes (31), executable by said central arithmetic processing unit (21), to write image data in said frame buffer (13); fourth instruction codes (31), executable by said control arithmetic processing unit (21), to specify areas of the image which are to be rewritten; and fifth instruction codes (32), executable by said central arithmetic processing unit (21), to determine, for each specified area of the image, lines of the image which are to be rewritten and which are to be specified, as a result of this determination, by said graphic controller (27) in execution of said second instruction codes (35). A raster scan display system comprised of: the raster scan display control apparatus (34,26,37) of claim 1; and a ferroelectric liquid crystal display device (15) operable by said control apparatus (34,26,37) to rewrite the specified lines of an image displayed thereon. A host system for use in the raster scan display system of claim 2, said host system (34) having: a central arithmetic processing unit (21); a main memory (23) to store currently executable instruction codes, and data for current use, respectively, for execution and use by said control arithmetic processing unit (21); a programme and data memory (24) containing programme instruction codes and data, transferable to said main memory (23) for current execution and use; and a bus controller (22) to control transfer of information and image data to and from said host system (34); said programme memory (24) of said host system (34) contains: third instruction codes (31), executable by said central arithmetic processing unit (21), to write image data in said frame buffer (13); fourth instruction codes (31), executable by said control arithmetic processing unit (21), to specify areas of the image which are to be rewritten; and fifth instruction codes (32), executable by said central arithmetic processing unit (21), to determine, for each specified area of the image, lines of the image which are to be rewritten.

Inventors: OHSHIMA MASAMICHI, OHSHIMA, MASAMICHI, OHSHIMA, MASAMICHI, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G09G3
IPC codes: G09G3, G02F1