Routines
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35940: Fill a region of attribute file with specified attribute (e.g. background colour and colour of text within)
Used by the routines at 32158, 32252, 32602, 34990 and 35828.
35940 LD BC,(23493) Load BC with the coordinates of the top-left corner of the area to fill
35944 CALL 54148 Load HL with attribute file address for coordinates (C, B)
The operand of the instruction at 35947 is an attribute value. This is modified by the instructions at 32170, 32411, 32440, 32613, 35064, 35842, 35853 and 35868.
35947 LD A,0 Load attribute to place into A
35949 LD (HL),A Apply attribute data to attribute file address in HL
35950 LD A,(23495) Load A with x-coordinate of right side of area to fill
35953 CP C Check if left and right edges are at same x-coordinate (i.e. zero width)...
35954 JP Z,35970 ...and if so, skip to 35970
35957 INC C Increase C
35958 LD A,C Copy C into A
35959 AND 31 Ensure current x-coordinate doesn't exceed 31 (i.e. width of screen)
35961 LD C,A Place back into C
35962 LD A,L Get LSB of attribute file address
35963 AND 224 Decrease to nearest multiple of 32 (i.e. start of character row in attribute file)
35965 ADD A,C Add x-offset (i.e. current x-coordinate, C)
35966 LD L,A Update HL with x-offset
35967 JP 35947 Loop back to 35947 to print next attribute block
35970 LD A,(23493) Get x-coordinate of left of area to fill
35973 LD C,A Store in C
35974 LD A,(23496) Get y-coordinate of bottom of area to fill
35977 CP B Compare with y-coordinate of top of area to fill
35978 RET Z If no difference between current y-coordinate and y-coordinate of bottom of area to fill then exit function and return
35979 INC B Advance current y-coordinate down one unit
35980 LD A,B Copy current y-coordinate into A...
35981 CP 24 ...and ensure it doesn't exceed 24 (i.e. height of screen)...
35983 JP NZ,35988 ...if it doesn't then skip ahead to 35988...
35986 LD B,0 ...else set current y-coordinate to zero (top of screen)
35988 CALL 54148 Load HL with attribute file address for coordinates (C, B)
35991 JP 35947 Loop back to print next attribute block row
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