Programmers - IRIS: Description and analysis of the effect.

IRIS.ss            
                               
music by IRONMAN               
(C) Ivan Roshchin, Moscow, 1998    
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   For the first time seeing this beautiful effect on
PC in the Dos Navigator program (screen sa-
ver 'iris.ss') I transferred it to the Spectrum.
Here is the full text of the program with details
comments:                           
                               
M_X EQU 7  ;     X scale                        
M_Y EQU 7  ;     Y scale                        
                               
        ORG #6000                                         
                               
;Set attributes:                                      
                               
        HALT                                                  
        LD HL,#5800        LD      DE,#5801                                      
        LD      BC,#2FF                                       
        LD      (HL),L                                        
        LDIR                                                  
                               
;Рисуем сетку:                                                
                               
        LD      HL,#4000                                      
LP1     LD      A,%01010101                                   
        BIT     0,H                                           
        JR      NZ,NE_FF                                      
        CPL                                                   
NE_FF   LD      (HL),AINC HL                                            
        LD A,H                                           
        CP #58                                           
        JR NZ,LP1                                        
                               
;Main loop:                                                
                               
MAIN_LP LD IX,BUFER+#2FF                                 
                               
;The buffer is filled "from end to beginning",                       
and in the same order it will be displayed                         
;to the screen in the TO_SCR procedure.                                 
                               
        LD H,TAB/#100                                    
        LD DE,(M_3)                                      
        LD A,24        
LOOP_V  EX      AF,AF'                                        
        LD      BC,(M_1)                                      
        EXX                                                   
        LD      B,32                                          
                               
LOOP_H  EXX                                                   
        LD      A,(MEM_BP)                                    
        LD      L,C                                           
        ADD     A,(HL)                                        
        LD      L,B                                           
        ADD     A,(HL)                                        
        LD      L,E                                           
        ADD A,(HL)                                        
        LD L,D                                           
 ADD A,(HL)                                        
        AND #7F                                           
                               
;The most significant bit of the accumulator is cleared, and the buffer is filled with the value 
;niyami #00-#7F. This will be useful in the TO_SCR procedure.            
                               
        LD (IX),A                                        
        DEC IX                                            
                               
        INC C  ;     !                                 
ADR_MX LD A,M_X                                         
        ADD A,B                                           
        LD B,A                               
                               
        EXX                                                   
        DJNZ    LOOP_H                                        
                               
        EXX                                                   
                               
ADR_MY  LD      A,M_Y                                         
        ADD     A,E                                           
        LD      E,A                                           
        INC     D     ;     !                                 
                               
        EX      AF,AF'                                        
        DEC     A                                             
        JP      NZ,LOOP_V                                     
                               
        LD      HL,(MEM_BP)                                   
        DEC     HL          ;     !!                          
        LD      (MEM_BP),HL                                   
                               
        LD      A,L                                           
        XOR     H                                             
        LD      HL,BUFER+#2FF                                 
        XOR     (HL)                                          
        XOR     E                                             
        XOR     C                                             
        ADD     A,D                                           
        ADD     A,B                                           
        LD      B,A                                           
                               
        LD      HL,NAPR                                       
        AND     3                                             
        LD      D,0                                           
        LD      E,A                                           
        ADD     HL,DE                                         
        LD      A,(HL)                                        
                               
        BIT     3,B                                           
        JR      NZ,TO_DEC                                     
                               
        CP      3                                             
        JP      P,TO_END                                      
        INC     (HL)                                          
        JR      TO_END                                        
                               
TO_DEC  CP      #FD                                           
        JP      M,TO_END                                      
        DEC     (HL)                                          
                               
TO_END  LD      A,(NAPR)                                      
        LD      HL,M_1                                        
        ADD     A,(HL)                                        
        LD      (HL),A                                        
                               
        LD      A,(M_2)                                       
        LD      HL,NAPR+1                 SBC     A,(HL)                                        
        LD      (M_2),A                                       
                               
        LD      A,(NAPR+2)                                    
        LD      HL,M_3                                        
        ADD     A,(HL)                                        
        LD      (HL),A                                        
                               
        LD      A,(M_4)                                       
        LD      HL,NAPR+3                                     
        SBC     A,(HL)                                        
        LD      (M_4),A                                       
                               
        CALL    TO_SCR  ;     Вывод на экранXOR     A       ;     Что-то                          
        IN      A,(254) ;     нажато?                         
        CPL                                                   
        AND     31                                            
        JR      NZ,OBR_Z                                      
                               
;Если не нажато, восстанавливаем масштаб по X и Y:            
                               
        CALL    INC_M                                         
        JP      MAIN_LP                                       
                               
;Нажата клавиша Z (Zoom) ?                                    
                               
OBR_Z   LD      A,#FE                                         
        IN      A,(254) BIT     1,A                                           
        RET     NZ   ;     Если нет - выходим                 
                               
;Если нажата - изменяем масштаб:                              
                               
        CALL    DEC_M                                         
        JP      MAIN_LP                                       
                               
MEM_BP  DW  0                                                 
M_1     DB  0                                                 
M_2     DB  0                                                 
M_3     DB  0                                                 
M_4     DB  0                                                 
NAPR    DB  2,1,3,4                                           
                               
;Процедуры INC_M и DEC_M увеличивают и уменьшают масштаб:     
                               
INC_M   LD      HL,ADR_MX+1                                   
        LD      A,(HL)                                        
        CP      M_X                                           
        JR      NC,INC_Y                                      
        INC     (HL)                                          
INC_Y   LD      HL,ADR_MY+1                                   
        LD      A,(HL)                                        
        CP      M_Y                                           
        RET     NC                                            
        INC     (HL)                                          
        RET                                                   
                               
DEC_M   LD      HL,ADR_MX+1                                   
        LD      A,(HL)                                        
        AND     A                                             
        JR      Z,DEC_Y                                       
        DEC     (HL)                                          
DEC_Y   LD      HL,ADR_MY+1                                   
        LD      A,(HL)                                        
        AND     A                                             
        RET     Z                                             
        DEC     (HL)             RET                                                   
                               
;The TO_SCR procedure recodes bytes from the buffer using the pas-  
;liters and outputs the result to the attribute file:                  
                               
TO_SCR LD HL,PALETTE  ;     palette                   
        LD DE,#5800  ;     screen                     
        LD BC,BUFER+#2FF  ;     end of the buffet               
                               ;ra                            
                               
        HALT                                                  
LP_S LD A,(BC)                                        
        LD L,A                                           
        LDI                                                   
                               
;I.e.  take a byte from the buffer and place it in the L register. This will be;offset in the palette (that's why it should start with the address-
;sa, multiple #100). The LDI command will take a byte from the palette (HL)
;and will place it on the screen at address (DE), which will increase by 1.
;The position in the buffer (BC) will decrease by 1. That HL also
;increases by 1, does not play any role, because H does not change-
;is present (because the buffer contains values 0..#7F), and L is all
;will change equally in the next step.                           
                               
        LD A,(BC)                                        
        LD L,A                                           
        LDI                                                   
        LD A,(BC)                                        
        LD L,A                                           
        LDI                                                   
        LD A,(BC)                                        
        LD L,A                                    
        LDI                                                   
        LD      A,(BC)                                        
        LD      L,A                                           
        LDI                                                   
        LD      A,(BC)                                        
        LD      L,A                                           
        LDI                                                   
        LD      A,(BC)                                        
        LD      L,A                                           
        LDI                                                   
        LD      A,(BC)                                        
        LD      L,A                                           
        LDI                                                   
        LD      A,D                                           
        CP      #5B                                           
        JP      NZ,LP_S                                       
                               
        RET                                                   
                               
;Вспомогательные буферы и таблицы:                            
                               
        ORG     #C000                                         
                               
;Вспомогательная таблица, начинается с адреса, кратного #100: 
                               
TAB     DB #40,#40,#40,#40,#40,#40,#40,#40                    
        DB #3F,#3F,#3F,#3F,#3F,#3E,#3E,#3EDB #3E,#3D,#3D,#3D,#3C,#3C,#3B,#3B                    
        DB #3B,#3A,#3A,#39,#39,#38,#38,#37                    
        DB #37,#3б,#35,#35,#34,#34,#33,#32                    
        DB #32,#31,#30,#30,#2F,#2E,#2E,#2D                    
        DB #2C,#2C,#2B,#2A,#29,#29,#28,#27                    
        DB #2б,#25,#25,#24,#23,#22,#22,#21                    
        DB #20,#1F,#1E,#1E,#1D,#1C,#1B,#1B                    
        DB #1A,#19,#18,#17,#17,#1б,#15,#14                    
        DB #14,#13,#12,#12,#11,#10,#10,#0F                    
        DB#0E,#0E,#0D,#0C,#0C,#0B,#0B,#0A                    
        DB #09,#09,#08,#08,#07,#07,#0б,#0б                    
        DB #05,#05,#05,#04,#04,#03,#03,#03                    
        DB #02,#02,#02,#02,#01,#01,#01,#01                    
        DB #01,#00,#00,#00,#00,#00,#00,#00                    
        DB #00,#00,#00,#00,#00,#00,#00,#00                    
        DB #01,#01,#01,#01,#01,#02,#02,#02                    
        DB #02,#03,#03,#03,#04,#04,#05,#05                    
        DB #05,#0б,#0б,#07,#07,#08,#08,#09                    
        DB #09,#0A,#0B,#0B,#0C,#0C,#0D,#0E                    
        DB #0E,#0F,#10,#10,#11,#12,#12,#13                    
        DB #14,#14,#15,#1б,#17,#17,#18,#19                    
        DB #1A,#1B,#1B,#1C,#1D,#1E,#1E,#1F                    
        DB #20,#21,#22,#22,#23,#24,#25,#25                    
        DB #2б,#27,#28,#29,#29,#2A,#2B,#2C                    
        DB #2C,#2D,#2E,#2E,#2F,#30,#30,#31                    
        DB #32,#32,#33,#34,#34,#35,#35,#3б                    
        DB #37,#37,#38,#38,#39,#39,#3A,#3A                    
        DB #3B,#3B,#3B,#3C,#3C,#3D,#3D,#3D                    
        DB#3E,#3E,#3E,#3E,#3F,#3F,#3F,#3F                    
        DB #3F,#40,#40,#40,#40,#40,#40,#40                    
                               
;Палитра, определяющая цвет эффекта, начинается с адреса,     
;кратного #100:                                               
                               
PALETTE DB #09,#09,#09,#09,#09,#09,#09,#09                    
        DB #09,#09,#09,#0B,#0B,#0B,#0B,#0B                    
        DB #0B,#0B,#0B,#0B,#0B,#0B,#1B,#1B                    
        DB #1B,#1B,#1B,#1B,#1B,#1B,#1B,#1B                    
        DB #1A,#1A,#1A,#1A,#1A,#1A,#1A,#1A                    
        DB #1A,#1A,#1A,#12,#12,#12,#12,#12                    
        DB#12,#12,#12,#12,#12,#12,#1б,#1б                    
        DB #1б,#1б,#1б,#1б,#1б,#1б,#1б,#1б                    
        DB #3б,#3б,#3б,#3б,#3б,#3б,#3б,#3б                    
        DB #3б,#3б,#3б,#34,#34,#34,#34,#34                    
        DB #34,#34,#34,#34,#34,#34,#24,#24                    
        DB #24,#24,#24,#24,#24,#24,#24,#24                    
        DB #25,#25,#25,#25,#25,#25,#25,#25                    
        DB #25,#25,#25,#2D,#2D,#2D,#2D,#2D                    
        DB #2D,#2D,#2D,#2D,#2D,#2D,#29,#29                    
        DB #29,#29,#29,#29,#29,#29,#29,#29;Intermediate buffer, can start at any address:       
                               
BUFER DS #300                                              
             _____             
                               
   How can you experiment with this
program:                              
   - change the scale (constants M_X and
M_Y). This can also be done directly
while the program is running by pressing the key
'Z'.                                     
   - instead of the commands INC C and INC D, place
enlarged "!", you can put commands that increase
reducing (or decreasing) C registers and
D not by 1, but by any other number.      
   - DEC HL command marked "!!",
can be replaced with several such commands
(or, for example, INC HL commands).          
   - change the contents of the TAB table.    
   - change the set of colors using pa-
liters (PALETTE array).                  
   You can change all the above parameters
parameters and directly during operation
program, if you make it self-modifying
swearing.                                
                               
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