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First working linedraw
This commit is contained in:
Dave Plummer
parent
40eb17c86c
commit
9e34ee0509
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@ -75,13 +75,26 @@ scroll_dest_hi: .res 1
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.segment "DATA"
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; Arguments for graphics functions
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_x1cord: .res 2
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_x2cord: .res 2
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_y1cord: .res 2
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_y2cord: .res 2
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_cursorX: .res 1
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_cursorY: .res 1
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tempchar: .res 1
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; Linedraw
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dx: .res 2
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dy: .res 2
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e2: .res 2
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sx: .res 1
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sy: .res 1
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dltemp: .res 2
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; DrawCircle
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xval: .res 2 ; These could move to zeropage for perf, but presume we
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yval: .res 2 ; we want to minimize the amount we grow zero page use
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err: .res 2
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@ -107,58 +120,58 @@ y0: .res 2
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;-----------------------------------------------------------------------------------
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; Based on MTU PIXADR code
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;-----------------------------------------------------------------------------------
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; x - _x1cord (16-bit)
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; y - _y1cord (16-bit)
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; adp1 - address of pixel to set (16-bit)
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; In: _x1cord (16-bit)
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; _y1cord (16-bit)
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; Out: adp1 (16-bit) Address of pixel to set
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;-----------------------------------------------------------------------------------
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_GetPixelAddress:
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lda _x1cord ; compute bit address first
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sta adp1 ; also transfer _x1cord to adp1
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and #$07 ; + which is simply the low 3 bits of x
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lda _x1cord ; compute bit address first
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sta adp1 ; also transfer x1cord to adp1
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and #$07 ; + which is simply the low 3 bits of x
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sta btpt
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lda _x1cord+1 ; finish transferring _x1cord to adp1
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lda _x1cord+1 ; finish transferring x1cord to adp1
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sta adp1+1
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lsr adp1+1 ; double shift adp1 right 3 to get
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ror adp1 ; int(xcord/8 )
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lsr adp1+1 ; double shift adp1 right 3 to get
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ror adp1 ; int(xcord/8 )
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lsr adp1+1
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ror adp1
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lsr adp1+1
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ror adp1
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sec ; and temporary storage
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lda _y1cord
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sta adp2
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sta temp
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lda _y1cord+1
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lda #0
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sbc _y1cord+1
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sta adp2+1
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sta temp+1
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asl adp2 ; compute 40*(_y1cord)
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rol adp2+1 ; 2*(_y1cord)
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asl adp2 ; compute 40*(y1cord)
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rol adp2+1 ; 2*(y1cord)
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asl adp2
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rol adp2+1 ; 4*(_y1cord)
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lda adp2 ; add in temporary save of (_y1cord)
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clc ; to make 5*(_y1cord)
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rol adp2+1 ; 4*(y1cord)
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lda adp2 ; add in temporary save of (y1cord)
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clc ; to make 5*(y1cord)
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adc temp
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sta adp2
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lda adp2+1
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adc temp+1
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sta adp2+1 ; 5*(_y1cord)
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asl adp2 ; 10*(_y1cord)
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sta adp2+1 ; 5*(y1cord)
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asl adp2 ; 10*(1cord)
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rol adp2+1
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asl adp2 ; 20#(_y1cord)
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asl adp2 ; 20#(y1cord)
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rol adp2+1
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asl adp2 ; 40*(_y1cord)
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asl adp2 ; 40*(y1cord)
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rol adp2+1
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lda adp2 ; add in int(_x1cord/8) computed earlier
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lda adp2 ; add in int(x1cord/8) computed earlier
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clc
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adc adp1
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sta adp1
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lda adp2+1
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adc adp1+1
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adc #>SCREEN ; add in base vidscreen address
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sta adp1+1 ; final result
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rts ; return
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adc #>SCREEN ; add in vmorg*256
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sta adp1+1 ; final result
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rts ; return
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;-----------------------------------------------------------------------------------
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; Mask tables for individual pixel subroutines
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@ -814,8 +827,8 @@ loadChar: lda (adp1), y
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doneText: rts
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demoText1: .byte " *** COMMODORE KIM-1 SHELL V0.1 ***", $0A, $0A
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.byte " 60K RAM SYSTEM. 49152 BYTES FREE.", $0A, $0A
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.byte "READY.", $0A, 00
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.byte " 60K RAM SYSTEM. 49152 BYTES FREE.", $0A, $0A, $00
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readyText: .byte "READY.", $0A, 00
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alphabet: .byte "ABCDEFGHIJKLMNOPQRSTUVWXYZ", 00, "*****", 00
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@ -825,21 +838,22 @@ _Demo: lda #0
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ldx #<demoText1
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ldy #>demoText1
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jsr _DrawText
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: ldx #<alphabet
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rts
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: ldx #<alphabet
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ldy #>alphabet
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jsr _DrawText
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jmp :-
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;-----------------------------------------------------------------------------------
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; DrawCircle - Draws a circle in video memory of a given radius at a given coord
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; DrawLine - Draws a line between two points
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;-----------------------------------------------------------------------------------
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; _x1cord (16-bit)
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; _y1cord (8-bit)
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; _y1cord ( 8-bit)
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; _x2cord (16-bit)
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; _y2cord (8-bit)
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; _y2cord ( 8-bit)
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;-----------------------------------------------------------------------------------
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; Implements something like Bresenham's algorithm for drawing a line
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; Implements something like Bresenham's algorithm for drawing a line:
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;-----------------------------------------------------------------------------------
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; void DrawLine(int x0, int y0, int x1, int y1, byte val)
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; {
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@ -870,181 +884,140 @@ _Demo: lda #0
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; }
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;-----------------------------------------------------------------------------------
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dx: .res 2
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dy: .res 2
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e2: .res 2
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sx: .res 1
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sy: .res 1
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dltemp: .res 2
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_DrawLine: lda _x2cord ; Calculate dx = (x2cord - X1cord)
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_DrawLine: ldx #$01 ; positive x-step for now
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stx sx
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lda _x2cord ; Calculate dx = (x2cord - X1cord)
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sec
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sbc _x1cord
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sta dx
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lda _x2cord+1
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sbc _x1cord+1
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sta dx+1
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bpl positivedx ; dx is positive, so we're good
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bpl calcdy ; dx is positive (dx >= 0), so we're good
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lda dx ; dx is negative, so compute absolute value
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clc ; by inverting bits and adding 1
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eor #$ff
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adc #1
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ldx #$FF ; negative x-step
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stx sx
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lda _x1cord ; Calculate dx = (x2cord - X1cord)
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sec
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sbc _x2cord
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sta dx
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lda dx+1
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eor #$ff
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adc #0
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lda _x1cord+1
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sbc _x2cord+1
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sta dx+1
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positivedx:
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lda _y2cord ; Calculate dy = (y2cord - y1cord)
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calcdy: ldx #$01 ; positive y-step for now
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stx sy
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lda _y2cord
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sec
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sbc _y1cord
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sta dy
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lda _y2cord+1
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sbc _y1cord+1
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sta dy+1
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bpl positivedy ; dy is positive, so we're good
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lda dy ; It's negative, so compute the absolute value
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clc ; by inverting bits and adding 1
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eor #$ff
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adc #1
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bcs positivedy ; If y2cord > y1cord, then dy is positive and we're good
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ldx #$FF ; negative y-step
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stx sy
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lda _y1cord
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sec
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sbc _y2cord
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sta dy
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lda dy+1
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eor #$ff
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adc #0
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sta dy+1
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positivedy: ; Check if dx > dy
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lda dy+1
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cmp dx+1
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bcc dxgt
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bne dygt
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positivedy: lda dx+1 ; Check if dx > dy (both are always positive now)
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bne dxgt ; If MSB of dx is greater than zero, then dx > dy since dy is 8-bits
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lda dy
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cmp dx
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bcs dygt
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bcs dygte
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dxgt: lda dx ; We found dx>dy so err = dx
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dxgt: lda dx ; We found dx>dy so set err = dx / 2
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sta err
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lda dx+1
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sta err+1
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jmp div2
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dygt: lda dy ; else err = -dy
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clc
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eor #$ff
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adc #1
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sta err
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lda dy+1
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eor #$ff
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adc #0
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sta err+1
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div2: clc
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lsr err+1 ; err /= 2
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lsr
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sta err+1 ; err = dx/2
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ror err
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jmp loop
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calcsx: lda _x1cord+1 ; if (x1cord < x2cord) then sx = 1
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cmp _x2cord+1
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bcc x1lt
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bne x1gt
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lda _x1cord
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cmp _x2cord
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bcc x1lt
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x1gt: lda #$FF
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sta sx
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bne calcsy
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x1lt: lda #1 ; otherwise sx = 1
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sta sx
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calcsy: lda _y1cord+1 ; if (y1cord < y2cord) then sy = 1
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cmp _y2cord+1
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bcc y1lt
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bne y1gt
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lda _y1cord
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cmp _y2cord
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bcc y1lt
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y1gt: lda _y1cord ; if (_y1cord > _y2cord) then sy = -1
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dygte: lda #0 ; we found dx <= dy so set err = -dy / 2
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sec
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sbc dy ; else err = -dy / 2
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ror
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ora #$80
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sta err
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lda #$FF
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sta sy
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bne loop
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y1lt: lda #1 ; otherwise sy = 1
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sta sy
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sta err+1
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loop: jsr _SetPixel ; Plot the current _x1cord, _y1cord
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lda _x1cord ; if (_x1cord == _x2cord && _y1cord == _y2cord) then we rts
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cmp _x2cord
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bne noteq
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lda _x1cord+1
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cmp _x2cord+1
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bne noteq
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lda _y1cord
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cmp _y2cord
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bne noteq
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lda _y1cord+1
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cmp _y2cord+1
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lda _x1cord+1
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cmp _x2cord+1
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bne noteq
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rts
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noteq: lda err
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noteq: lda err ; e2 = err
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sta e2
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lda err+1
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sta e2+1
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lda e2 ; if (e2 > -dx) is the same as if (e2 + dx > 0), so we test that.
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clc ; If its true then we dec err and inc _x1cord
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lda e2 ; if (e2 > -dx) is the same as if (e2 + dx > 0), so we test that because its easier
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clc ; If its true then we dec err and inc _x1cord
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adc dx
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sta temp
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lda e2+1
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adc dx+1
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bmi noincx
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bmi doneupdatex ; If result is negative, then e2 + dx < 0, so we don't dec err or inc _x1cord
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bne stepx ; If MSB is non-zero, then e2 + dx > 0, so we DO dec err and inc _x1cord
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lda temp ; If result is zero in MSB, then we check the LSB here
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beq doneupdatex ; If LSB is zero, then we don't dec err or inc _x1cord
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; We already know e2 + dx > 0, so LSB can't be negative
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stepx: lda sx
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bmi decx
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incxval: inc _x1cord ; _x1cord += 1 because sx == 1
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bne updatexerr
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inc _x1cord+1
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jmp updatexerr
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incx: lda err ; err -= dy
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decx: lda _x1cord ; _x1cord += 1 because sx == 1
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sec
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sbc #1
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sta _x1cord
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lda _x1cord+1
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sbc #0
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sta _x1cord+1
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updatexerr: lda err ; err -= dy
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sec
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sbc dy
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sta err
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lda err+1
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sbc dy+1
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sbc #0
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sta err+1
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lda _x1cord ; _x1cord += sx
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clc
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adc sx
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sta _x1cord
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lda _x1cord+1
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adc #0
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sta _x1cord+1
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noincx: lda e2+1 ; if (e2 < dy) then we inc err and inc _y1cord
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cmp dy+1
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bcc noincy
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bne incy
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lda e2
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cmp dy
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bcc noincy
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incy: lda err ; err += dx
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doneupdatex:lda e2+1 ; if (e2 < dy) then we inc err and inc _y1cord
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bmi updateerry ; If MSB is negative, then e2 < dy, so we inc err and inc _y1cord
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bne noupdatey ; If the MSB of e2 is set and positive, then we know e2 > dy, so we don't inc err or inc _y1cord
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lda e2
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sec
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sbc dy
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beq noupdatey ; e2 - dy == 0 so we don't inc err or inc _y1cord
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bcs noupdatey ; if e2 was large enough that carry never cleared, then e2 > dy do no update
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updateerry: lda err ; err += dx
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clc
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adc dx
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sta err
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lda err+1
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adc dx+1
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sta err+1
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lda _y1cord ; _y1cord += sy
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stepy: lda _y1cord
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clc
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adc sy
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sta _y1cord
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lda _y1cord+1
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adc #0
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sta _y1cord+1
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noincy:
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jmp loop
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noupdatey: jmp loop
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