Nonsense - the routine pointer with detailed explanations.

<b>Nonsense</b> - the routine pointer with detailed explanations.

                          in basic ...

(C) Pix / BrC Izhevsk



      you once again main coder of
Brutal Creators (forgive me Noviset).
Today, I will fail to theme building
cursor. Of course, I did not spec in this area, and if you need 
a cool and fast pointer, it is that you read the counter. If 
you poboku escarpment, then read on.


   Behold, now there were only those who are not
find articles on a cursor, or those who are guided by the 
principle of "if only to sing, and also those who are not very 
steep in the codes and wants to understand how the STE it, damn 
it, it works. For the latter, and wrote this article. 

   I'll start with the problems arising from the most
beginerskih coders. Often the first handwritten cursor 
disappears top of the Scrin, or begins to flicker.

I'll try to explain what is happening.
For this we consider the principle of construction
images on the screen. As we know, there is a wonderful event
50 times per second, immediately after the arrival
interrupts. The cursor is usually constructed to handle the 
interrupt, thus cursor and images are constructed 
simultaneously. The procedure for processing interrupt occurs 
approximately the following:


   a) restore the image under the old cursor (erase it);

   b) store the image in a new position;

   c) construct a new cursor;
Thus we must do all 3 points to
such time as the video controller builds
image above the cursor position (old and new). Typically, the 
braking procedure no time to draw up a new cursor

the point where its location
starts is displayed on the monitor, so we
it and do not see. Hence the rule: to build a new cursor, until 
the Border is drawn, and it requires a relatively fast 
procedure. <Much the same can be read the ZF # 3>.


   Well, pristipim:
BEGXP EQU 184; initial coordinates
BEGYP EQU 0; y = 184 x = 0
XY_KOOR DB BEGXP, BEGYP; current coordinates.

   Our procedures have to be quick,
For all the complex (brake) calculations
sdelaem once. For example, Sprite print up to a pixel can only
y-ku, and the x step discrete (8pix). But we
need to print both y, and the x with the same accuracy of 1 
pixel. To do this, move the sprite on the number of pixels 
equal to the remainder of the division by 8. ie if x = 10, p = 
x% 8 = 2, then you need to move sprite 2 piskela right, and 
then print it in the position x / 8 (char), y (pixel). This can 
be done in the printing process, but it will be slow, therefore 
we make to our original sprite another 7 obrazovnnyh from it by 
the shift. They are something we'll use in the process of 
withdrawal. This entire mutenyu will deal with initialization 
procedure: INIT_CUR; proper initialization procedure cursor.


        LD A, BEGXP

        LD (XY_KOOR), A

        LD A, BEGYP

        LD (XY_KOOR +1), A

   Create a table of addresses for quick screen printing Y. To 
do this, will go to all line from 0 to 192 and write the 
address of their beginnings in Tabl_adr. INT_TAB LD DE, # 4000; 
top display area 

        LD HL, TABL_ADR; HL = address of table

        LD B, 192; number of rows
INT_TB1 LD (HL), D; enters the address of the string, which

        INC HL; in DE.

        LD (HL), E; ..

        INC HL; ..

        CALL DOWN_DE; calculate the address of the next line

        DJNZ INT_TB1; will go to all the rows.
 Now create the sprites, as mentioned above. At the same time 
mixing it with mask.


        LD HL, SUR_CUR; original sprite

        LD DE, CURSPR; there will be slipping.

        LD BC, 32; length of a sprite with a mask

        LDIR; first - offset # 00
INT_SPR LD B, 8; like the number of new Sprite.

        LD DE, NEW_SPR; new sprite written.
INT_SP0 PUSH BC; for the cycle:)

        LD HL, CURSPR; beginning Sprite

        LD IX, CURSPR +16; top of the mask

        LD B, 16; length of Sprite or masks
INT_SP1 LD A, (IX); take the mask

        LD (DE), A; put where it is necessary

        INC DE; seq. ale.

        LD A, (HL); take Sprite

        LD (DE), A; Kalda.

        INC DE; seq.

        INC HL; sled.spr.

        INC IX; neht.mask.

        DJNZ INT_SP1; well, a cycle like that.

   That, mixed with sprite mask now
have a Sprite with a mask in the format mask
Sprite mask, Sprite ... offset # 00.Teper will move.

        LD HL, CURSPR; outcome for the displacements.

        LD B, 8; height, such as
INT_SP2 LD A, (HL); take

        OR A; cy = 0

        RRA; ->

        LD (HL), A; we put in place

        INC HL; seq.

        LD A, (HL); take the second byte of Sprite

        RRA; ->

        LD (HL), A; put

        INC HL; further

        DJNZ INT_SP2; and so on ...

        LD HL, CURMASK;

        LD B, 8;
INT_SP3 LD A, (HL); Tozha thing for masks

        SCF; cy = 1

        RRA; ->

        LD (HL), A;

        INC HL;

        LD A, (HL);

        RRA;

        LD (HL), A;

        INC HL;

        DJNZ INT_SP3; with masks all ...


        POP BC;

        DJNZ INT_SP0; seq. displacement trace. Sprite

        LD A, # 37;

        LD (CUR_PR), A; some presets

        JP PR_CUR_; well and everything installs completed, 
there will be                               ; Trolled first 
kurosr. 

DOWN_DE INC D; percent address calculation followed by a string

        LD A, D; from the previous address. Standard.

        AND 7

        RET NZ

        LD A, E

        ADD A, # 20

        LD E, A

        RET C

        LD A, D

        SUB 8

        LD D, A

        RET


  Now the routine cursor. Here,
like, it's simple: a little mathematics, very little. No stack 
output. Speed is reached no shift

spritov.Zdes same familiarity percent recovery under the old 
cursor. I think, figure it out, I'm lazy ... :) 

PR_CUR LD A, 0

        LD B, 0

        LD C, A

        SLA C

        RL B

        LD HL, TABL_ADR

        ADD HL, BC

        LD D, (HL)

        INC HL

        LD E, (HL)
PR_CUR0 LD A, 0

        SRL A

        SRL A

        SRL A

        ADD A, E

        LD E, A

        JR NC, PRCO

        INC D
PRCO LD HL, SPR_BUF

        LD B, 8
PRC__ LD A, (HL)

        INC HL

        LD (DE), A

        INC DE

        LD A, (HL)

        LD (DE), A

        DEC DE

        INC HL

        CALL DOWN_DE

        DJNZ PRC__
WOST_PR OR A

        RET C
PR_CUR_ LD A, (XY_KOOR)

        LD (PR_CUR +1), A

        LD B, 0

        LD C, A

        SLA C

        RL B

        LD HL, TABL_ADR

        ADD HL, BC

        LD D, (HL)

        INC HL

        LD E, (HL)

        LD A, (XY_KOOR +1)

        LD (PR_CUR0 +1), A

        SRL A

        SRL A

        SRL A

        ADD A, E

        LD E, A

        JR NC, PRC0

        INC D
PRC0 LD A, (XY_KOOR +1)

        AND 7

        LD BC, NEW_SPR

        LD H, 0

        LD L, A

        ADD HL, HL

        ADD HL, HL

        ADD HL, HL

        ADD HL, HL

        ADD HL, HL

        ADD HL, BC

        LD IX, SPR_BUF

        LD B, 8
PRC1 LD A, (DE)

        LD (IX), A

        INC IX

        AND (HL); MASK

        INC HL

        XOR (HL); CUR

        INC HL

        LD (DE), A

        INC DE

        LD A, (DE)

        LD (IX), A

        INC IX

        AND (HL); MASK

        INC HL

        OR (HL); CUR

        INC HL

        LD (DE), A

        DEC DE

        CALL DOWN_DE

        DJNZ PRC1

        RET


   Well, load spritik cursor and mask.

SUR_CUR LCODE "CurSpr22.C"; fixed line noatr (sm5.11)


   What?! Long time no see so miserable
code? Wait, is not a write! After
we do not mind? Well, okay, all puhnite and
write four-thread, any thread can Wikipedia
to nonsense, and it'll only read my people
delirium.