apple-pascal-1.3-manual

DRA WBLOCK treats each boolean element of SOURCE as a dot-TRUE forwhite and FALSE for black. It copies the array of dots (or a portion of it)from memory onto the screen to form a screen image. The first dimension ofthe array is the number of rows in the array; the second dimension is thenumber of elements in each row.You may choose to copy the entire SOURCE array, or you may choose tocopy any specified "window" from the array, using only those dots in thearray from XSKIP to XS KIP+ WIDTH and from YSKIP to YSKIP+ HEIGHT.Furthermore, you can specify the starting screen position for the copy, at(XSCREEN,YSCREEN).The other DRA WBLOCK parameters have these meanings:o ROWSIZE is the number of bytes (not dots) per row in the array. You cancalculate this from the formulabytes = 2 * ((X + 15) DIV 16)where Xis the number of dots in each row.o XSKIP tells how many horizontal dots in the array to skip over before thecopying process is started.o YSKIP tells how many vertical dots in the array to skip over beforebeginning the copying process. Note that copies are made starting fromthe bottom up-i.e. the first row copied from the array is the bottom rowof the screen copy.o WIDTH tells how many dots' width of the array, starting at XSKIP, willbe used.o HEIGHT tells how many dots' height of the array, starting at YSKIP, willbe used.o XSCREEN and YSCREEN are the coordinates of the lower left corner ofthe area to be copied into. WIDTH and HEIGHT determine the size of therectangular area.o MODE ranges from 0 through 15. It determines what appears on theportion of the screen specified by the other parameters. It can simplysend white or black to the screen, regardless of what is in the array, copythe array literally, or combine the contents of the array and the screenand send the result to the screen. The following table specifies whatoperation is performed on the data in the array and on the screen, andthus what appears on the screen (A refers to the array, S to the screen).Although these modes are expressed in terms of black and white, theycan be used to create images of any value of SCREENCOLOR. Just useFILLSCREEN to create an area of solid color and then manipulate itlogically to represent the pattern in the array.III-204Chapter 11: Screen Graphics