Variable size character display without loss of obscured character positions
First Claim
1. A data display apparatus for displaying on a screen of a raster scan display device data represented by digital codes, the displayed data being comprised of discrete characters arranged in character rows each comprising a number of character positions, in which said digital codes represent both character data which identifies character shape and attribute data which identifies character size, said apparatus comprising, means for selectively displaying in accordance with the received data a character either normal size in one character position or enlarged size in at least two corresponding character positions in adjacent character rows, characterized in that said means includes a twin row buffer comprising two buffers each of which can hold the character and attribute data for all of the positions of a row of characters and of which one functions as a "fill" row buffer for receiving character and attribute data for a character row and the other as a "display" row buffer for providing such previously received data for the display of the preceding character row, and vice versa alternately, means operable in respect of each character position of the current "fill" row buffer for examining the corresponding character position in the current "display" row buffer and to insert into the "fill" row buffer position the attribute data for the "display" row buffer position, if the latter position is for the top half of an enlarged size character.
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Accused Products
Abstract
A data display arrangement in which selected characters arranged in rows of characters which are displayed on the screen of a CRT can be enlarged selectively at the expense of obscuring other characters, or of preventing other characters from being displayed enlarged size. The character size for a displayed character is determined by a size attribute code which accompanies the character code for the character. If an attribute code for a character is changed, the change in the size of the character as displayed can reveal previously obscured characters, which in turn may be displayed different size if an accompanying attribute code of that effect can now be implemented. These changes can result in ripple effects through the whole display. The invention provides a register and buffer arrangement in which character data and size attribute data for each character position of each character row is examined and altered in accordance with an "obscured character algorithm" which allows ripple effects to occur and ensures that data for display at obscured positions is not lost.
32 Citations
9 Claims
- 1. A data display apparatus for displaying on a screen of a raster scan display device data represented by digital codes, the displayed data being comprised of discrete characters arranged in character rows each comprising a number of character positions, in which said digital codes represent both character data which identifies character shape and attribute data which identifies character size, said apparatus comprising, means for selectively displaying in accordance with the received data a character either normal size in one character position or enlarged size in at least two corresponding character positions in adjacent character rows, characterized in that said means includes a twin row buffer comprising two buffers each of which can hold the character and attribute data for all of the positions of a row of characters and of which one functions as a "fill" row buffer for receiving character and attribute data for a character row and the other as a "display" row buffer for providing such previously received data for the display of the preceding character row, and vice versa alternately, means operable in respect of each character position of the current "fill" row buffer for examining the corresponding character position in the current "display" row buffer and to insert into the "fill" row buffer position the attribute data for the "display" row buffer position, if the latter position is for the top half of an enlarged size character.
- 7. A data display apparatus for displaying digital data on a screen of a raster scan display device in the form of rows of characters each comprising a number of character positions, said digital data composed of character data and attribute data, said apparatus comprising, means responsive to the digital data for selectively displaying characters in normal size in one character position or enlarged size in at least two corresponding character positions in adjacent character rows, first and second buffer registers each of which can store character and attribute data for all positions of a row of characters, said first and second buffers being operative alternately with one buffer functioning as a fill row buffer for receiving character and attribute data for a character row and the other buffer functioning as a display row buffer providing previously received data for display of a preceding character row, and vice versa, and means operable for each character position of the current fill row buffer for examining the corresponding character position in the current display row buffer to selectively supply attribute data to the fill row buffer as determined by the data present in the display row buffer.
Specification