Difference between revisions of "Homebrew:Scrolling Mountains"
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| − | Curtdawg figured out a nice way to make scrolling mountains like in the game Scramble. The variations can be set as data to control the various peaks and valleys, example code below. Could be used as a graphics engine for various types of games, none that has been made yet. Add a ship or helicopter and a few enemies and it's a game! | + | Curtdawg figured out a nice way to make scrolling mountains like in the game Scramble. A lot of bios calls are used which saves a lot of programming space. The variations can be set as data to control the various peaks and valleys, example code below. Could be used as a graphics engine for various types of games, none that has been made yet. Add a ship or helicopter and a few enemies and it's a game! |
Revision as of 16:43, 18 November 2012
Scrolling mountains in action.
Curtdawg figured out a nice way to make scrolling mountains like in the game Scramble. A lot of bios calls are used which saves a lot of programming space. The variations can be set as data to control the various peaks and valleys, example code below. Could be used as a graphics engine for various types of games, none that has been made yet. Add a ship or helicopter and a few enemies and it's a game!
; Scrolling Mountains
;
; written by Curtdawg
processor f8
;------------;
; BIOS Calls ;
;------------;
delay = $008f
prompt = $0099
clrscrn = $00D0
pushk = $0107
popk = $011e
RedVert12Line = $01F6
RedHoriz104Line = $020E
prompts = $0224
IncP1Score = $02AC
IncP2Score = $02B5
UpdateBall = $03D3
Clock = $0467
DetectCollision = $049C
unknown = $05FC
ResetFrameCounter = $065B
drawchar = $0679
drawcustomchar = $067C
eraseimageoldpos = $06EC
drawsquareimage = $0718
; Data Counter def
bitmaps = $767
;-------------------;
; Color Definitions ;
;-------------------;
red = $40
blue = $80
green = $00
bkg = $C0
clear = $FF
;--------------------;
; Register Reference ;
;--------------------;
; Reg8: Left edge where drawing begins: Initialized to SCREEN_WIDTH and decremented until 0
; Reg9: Flat pane index for column pointed to by Reg8
; RegB: Current height of Reg8 Column
; Reg4: Current Column
; Reg5: Current Flat pane index
; Reg7: Current Column Height
; Reg32: Op code byte for column pointed to by Reg8
; Reg1: Current Op code byte
;------------------;
; Object Variables ;
;------------------;
SCREEN_WIDTH = 101 ; 95
;===================;
; Main Program Code ;
;===================;
;---------------;
; Program Entry ;
;---------------;
org $800
LR $5,A ;
LR $A,A ;
cartridgeStart:
li $D0;
lr 3, A
pi clrscrn;
dci opcodes;
lr q,dc;
li SCREEN_WIDTH;
lr $8,A; ; actual left edge for drawing
clr;
lr $9,A; ; Flat plane index for column specified by $8
li $37
lr $B,A ; current height at column specified by $8
lisu 4;
lisl 0; ; reg 32 has current op code byte
lm;
oi $40
lr (IS), A;
DrawNextFrame:
bf $0,DrawScreen;
DrawScreenReturn:
ds $8;
bp DrawNextFrame;
clr;
lr $8,A; // Start column
bf $0,DrawNextFrame ;
DrawScreen:
lr dc,q;
lr A,$8 ; start column
lr $4,A ; reg4 stores current column
lr A,$B ; current column height
lr $7,A ; reg7 stores current column height
lr A,(IS) ; S has current op code
lr $1,A ; reg1 has current op code
lr A,$9 ; flat plane index
lr $5,A ; reg5 stores current flat plane index
DrawScreen.Loop:
oi $0; ; If we are drawing a flat plane, no need to update this column
bz SkipFlat;
ds $5;
bz NextColumn.NextOpcode ;
br NextColumn ;
SkipFlat:
lis $3 ; Get op code in low bits and transform to column height offset (0=-2,1=-1,2=1,3=2)
ns $1;
lr $0,A
ds $0
bz DecOffset;
bp skipDec;
DecOffset:
ds $0
skipDec:
pi UpdateColumnPixels ;
lr A,$0;
as $7 ; update currentColumn height
lr $7,A;
lr A,$1 ; advance to next 2-bit opcode in byte
sr 1
sr 1
lr $1,A
sr 1
bnz NextColumn;
NextColumn.NextOpcode:
lm ; Get next opcode
oi $0; // Is flat?
bp NotFlat;
ci $80
bnz Flat;
dci opcodes_repeat;
bf $0,NextColumn.NextOpcode;
Flat:
ni $3F;
lr $5,A;
bf $0,NextColumn ;
NotFlat:
oi $40
lr $1,A;
NextColumn:
lr A,$4
oi $0;
bnz IncColumn;
lr A,$7 ;
lr $B,A ;
lr A,$1 ;
lr (IS),A ;
lr A,$5 ;
lr $9,A ;
lr q,dc;
IncColumn:
lis $1;
as $4;
lr $4,A;
ci SCREEN_WIDTH + 1;
bz DrawScreenReturn;
lr A,$5 ; flat plane index
bf $0,DrawScreen.Loop ;
; Draws or erases 1 or 2 pixels in the current column
; Reg0: Code: $FE = Draw two pixels (Column, Row-1 and Column, Row-2)
; $FF = Draw one pixel (Column, Row-1)
; $01 = Erase one pixel (Column, Row)
; $02 = Erase two pixels (Column, Row and Column, Row + 1)
; Reg4: Column - We add 4 to this
; Reg7: Row - We add 4 to this
UpdateColumnPixels:
LI $40 ; Load Immediate $40
OUTS 0 ; Store in Port $0 (Why?)
lis $1
ns $7
li blue
bz SkipRed
li green
SkipRed:
outs 1; // Set color
lr A,$0;
ci $01;
bz EraseOnePixel;
bm EraseTwoPixels;
ci $FE;
bz DrawTwoPixels;
lis $4;
as $4;
com ;
outs 4;
lis $3;
as $7;
com;
ni $3F;
outs 5;
li $60
outs 0
li $50
outs 0
pop ; Don't delay - there will be a fair amount of processing before the next pixel is drawn
DrawTwoPixels:
li $4;
as $4;
com ;
outs 4;
lis $3;
as $7;
com;
ni $3F;
outs 5;
li $60
outs 0
li $50
outs 0
D2PDelay:
sr 1;
bnz D2PDelay; Delay for 31 cycles. Hopefully this is enough
lis $1
ns $7
li green
bz SkipRed2
li blue
SkipRed2:
outs 1; // Set color
lis $2;
as $7;
com;
ni $3F;
outs 5;
li $60
outs 0
li $50
outs 0
pop ; Don't delay - there will be a fair amount of processing before the next pixel is drawn
EraseOnePixel:
li $C0; // background
outs 1; // Set color
li $4;
as $4;
com ;
outs 4;
lis $4;
as $7;
com;
ni $3F;
outs 5;
li $60
outs 0
li $50
outs 0
pop ; Don't delay - there will be a fair amount of processing before the next pixel is drawn
EraseTwoPixels:
li $C0; // background
outs 1; // Set color
li $4;
as $4;
com ;
outs 4;
lis $4;
as $7;
com;
ni $3F;
outs 5;
li $60
outs 0
li $50
outs 0
E2PDelay:
sr 1;
bnz E2PDelay ; Delay for 31 cycles. Hopefully this is enough
lis $5;
as $7;
com;
ni $3F;
outs 5;
li $60
outs 0
li $50
outs 0
pop ; Don't delay - there will be a fair amount of processing before the next pixel is drawn
; high bit set means run of flat ground - count is in the lower bits if %1000000 then reset game data
; otherwise the three lower sets of two bots each encode an
; instruction: (00:up two), (01:up one), (10:down one), (11:down two),
; Warning comments for these opcodes are generally invalid as I've modified the opcodes without
; updating the comments. Sorry!
opcodes:
.byte %00000101 ; up 3 : 3
.byte %00010101 ; up 3 : 6
.byte %00010101 ; up 3 : 6
.byte %00010101 ; up 3 : 6
.byte %00010101 ; up 3 : 6
opcodes_repeat
.byte %00000000 ; up 3: 15
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00111111 ; down 3 : 12
.byte %10010000 ; flat 16
.byte %00000000 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %10000011 ; flat 3
.byte %00000000 ; up 3: 15
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00111111 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %10010000 ; flat 12
.byte %00000000 ; up 3: 15
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00111111 ; down 3 : 12
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00000000 ; up 6: 15
.byte %00000000 ; up 6: 15
.byte %10000100 ; flat 16
.byte %00000000 ; up 6: 15
.byte %00000000 ; up 6: 15
.byte %00111111 ; down 3 : 12
.byte %00000000 ; up 3: 15
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00111111 ; down 3 : 12
.byte %10010000 ; flat 16
.byte %00000000 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %10000011 ; flat 3
.byte %00000000 ; up 3: 15
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00111111 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %10010000 ; flat 12
.byte %00000000 ; up 3: 15
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00111111 ; down 3 : 12
.byte %00010101 ; up 3: 15
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00000000 ; up 6: 15
.byte %00000000 ; up 6: 15
.byte %10000100 ; flat 4
.byte %00000001 ; flat 16
.byte %00100110 ; flat 16
.byte %00011001 ; flat 16
.byte %00101111 ; up 6: 15
.byte %10000100 ; flat 4
.byte %00000000 ; up 6: 15
.byte %00000000 ; up 6: 15
.byte %00111111 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %00101010 ; down 3 : 12
.byte %10000000 ; restart
org $fff
.byte $ff
