Sparse_Invaders_Source_ _BlockDrawer.txt - simondotm/stardot-wiki GitHub Wiki
Blocks are basically 8 pixel by 8 pixel graphics that are drawn to the screen. Plotting to the screen is done as with characters, in that drawing a block to 2,1 would draw it at pixel coords of 16,8. Hmm I'm sure I will be revisiting this and trying to explain it a little better.
;-------------------------------------------------------------------------------
; BlockDrawer
; Written by Neil Beresford.
;
; Copyright 2008,2009 Neil Beresford
;
; This file is part of Sparse Invaders.
; Sparse Invaders is free software: you can redistribute it and/or modify
; it under the terms of the GNU General Public License as published by
; the Free Software Foundation, either version 3 of the License, or
; (at your option) any later version.
;
; Sparse Invaders is distributed in the hope that it will be useful,
; but WITHOUT ANY WARRANTY; without even the implied warranty of
; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
; GNU General Public License for more details.
;
; You should have received a copy of the GNU General Public License
; along with Sparse Invaders. If not, see <http://www.gnu.org/licenses/>.
;
;
; Notes:
; Draws the block to the screen - using character positioning...
; The blocks are 8 by 8...
;-------------------------------------------------------------------------------
.require "Constands"
.require "Macros"
;-------------------------------------------------------------------------------
;-------------------------------------------------------------------------------
;
;
;
;-------------------------------------------------------------------------------
BlockInit:
RTS
BlockColorDraw draws a soild coloured block to the position passed in. This is commented out, as wasn't needed with Invaders. But I've left the function here for reference.
;-------------------------------------------------------------------------------
; BlockColourDraw
; a - block colour
; x - characters across
; y - characters down
;
; This is not used in Invaders, so commented out.
;
;-------------------------------------------------------------------------------
;BlockColourDraw:
;
; ; store the sprite number, x and y position
; STA SCRATCH1
; STX XPOS
; STY YPOS
;
; ; calculate the screen position...
; LDA #SCREENLOW
; STA SCREENADD
; LDA #SCREENHIGH
; STA SCREENADD+1
;
; ; muli x by 32 then add to screen address
; STX TEMPPTR
; LDA #0
; STA TEMPPTR+1
; `MUL32 TEMPPTR
; `ADD16BIT TEMPPTR,SCREENADD,SCREENADD
;
; TYA
; ASL
; TAY
; LDA LookUp640, Y
; ADC SCREENADD
;; STA SCREENADD
; INY
; LDA LookUp640,Y
; ADC SCREENADD+1
; STA SCREENADD+1
;
;
; ; lets do a coloured block for now...
; LDA SCREENADD
; STA BCD_ScrPtr+1
; LDA SCREENADD+1
; STA BCD_ScrPtr+2
;
; ; the draw ...
;
; LDX #4
;
;BCD_Height:
;
; LDY #7
;
;BCD_Draw:
;
; LDA SCRATCH1
;BCD_ScrPtr:
; STA $ffff,Y
; DEY
; BPL BCD_Draw
;
; LDA BCD_ScrPtr+1
; CLC
; ADC #8
; STA BCD_ScrPtr+1
; LDA BCD_ScrPtr+2
; ADC #0
; STA BCD_ScrPtr+2
;
; DEX
; BNE BCD_Height
;
; RTS
BlockDraw draws a block graphic to the passed in position on the screen. Block graphics include the font for the text, the score, the lifes etc. You will notice after this function the 'blocks' are incbin'ed along with the look up table to quickly calculated screen positions.
;-------------------------------------------------------------------------------
; BlockDraw - a - block number
; x - characters across
; y - characters down
;-------------------------------------------------------------------------------
BlockDraw:
; store the sprite number, x and y position
STA SCRATCH1
STX XPOS
STY YPOS
; calculate the screen position...
LDA #SCREENLOW
STA SCREENADD
LDA #SCREENHIGH
STA SCREENADD+1
; muli x by 32 then add to screen address
STX SCREENPTR
LDA #0
STA SCREENPTR+1
`MUL32 SCREENPTR
`ADD16BIT SCREENPTR,SCREENADD,SCREENADD
TYA
ASL
TAY
LDA LookUp640, Y
ADC SCREENADD
STA SCREENADD
INY
LDA LookUp640,Y
ADC SCREENADD+1
STA SCREENADD+1
; calculate the gfx for the block data...
LDA SCRATCH1
ASL
TAX
CLC
LDA BlockData,X
ADC #2
ADC #<BlockData
STA CURRENTSPRITEDATA
INX
LDA BlockData,X
ADC #>`BlockData`
STA CURRENTSPRITEDATA+1
; setup the screen position
LDA SCREENADD
STA BD_ScrPtr+1
LDA SCREENADD+1
STA BD_ScrPtr+2
LDA CURRENTSPRITEDATA
STA BD_GfxPtr+1
LDA CURRENTSPRITEDATA+1
STA BD_GfxPtr+2
; the draw ...
LDX #4
BD_Height:
LDY #7
BD_Draw:
BD_GfxPtr:
LDA $ffff,Y
BD_ScrPtr:
STA $ffff,Y
DEY
BPL BD_Draw
LDA BD_ScrPtr+1
CLC
ADC #8
STA BD_ScrPtr+1
LDA BD_ScrPtr+2
ADC #0
STA BD_ScrPtr+2
LDA BD_GfxPtr+1
CLC
ADC #8
STA BD_GfxPtr+1
LDA BD_GfxPtr+2
ADC #0
STA BD_GfxPtr+2
DEX
BNE BD_Height
RTS
;-------------------------------------------------------------------------------
BlockData:
.incbin "Blocks"
LookUp640:
.incbin "LookUpTable640"
;-------------------------------------------------------------------------------
; End of BlockDrawer
;-------------------------------------------------------------------------------