User Tools

Site Tools


base:sprite_x-coordinate_calculus

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

base:sprite_x-coordinate_calculus [2015-04-17 04:34] (current)
Line 1: Line 1:
 +===== Signed Sprite X-Coordinate calculus: by delta table =====
 +
 +This piece of code adds a signed byte (from the delta table) to an unsigned byte (the sprite x-coordinate) and returns a unsigned 9-bit number, storing the lower 8-bits on the sprite x-coordinate register and 9th bit on the sprite x-coordinate MSB register.
 +
 +<code>
 + ;Calc new sprite 0 X-coordinate by delta table
 +        ;by The_WOZ/soft154i
 +
 +        ; XDELTA = delta table for X
 +        ; y register = XDELTA index
 + clc
 + clv
 + lda $D000           ;Load first operand: sprite0 x-coordinate
 + bmi .pxa0           ;Test sign of first operand
 + adc XDELTA,y ;First operand is positive (in 2's complement)
 + sta $D000
 + bpl .cnt
 + bvs .cnt
 + lda #$fe ;Reset MSB
 + and $D010
 + jmp .pxm0
 +.pxa0
 + adc XDELTA,y ;First operand is negative
 + sta $D000
 + bvs .cnt
 + bcc .cnt
 + bmi .cnt
 + lda #$01 ;Set MSB
 + ora $D010
 +.pxm0 sta $D010
 +
 +.cnt    ;--- Rest of the program ---
 +
 +; X Delta table, ACME format
 +XDELTA !byte 5,6,5,6,5,6
 +      !byte 5,5,5,5,5,4
 +      !byte 4,4,4,4,3,4
 +      !byte 3,2,3,2,2,2
 +      !byte 1,1,1,1,0,0
 +      !byte 0,0,0,-1,-1,-1
 +      !byte -1,-1,-1,-2,-2,-1
 +      !byte -2,-2,-2,-2,-1,-2
 +      !byte -2,-2,-1,-2,-2,-1
 +      !byte -2,-1,-1,-1,-1,0
 +      !byte -1,0,-1,0,0,1
 +      !byte 0,1,0,1,1,1
 +      !byte 1,2,1,2,2,1
 +      !byte 2,2,2,1,2,2
 +      !byte 2,2,1,2,2,1
 +      !byte 1,1,1,1,1,0
 +      !byte 0,0,0,0,-1,-1
 +      !byte -1,-1,-2,-2,-2,-3
 +      !byte -2,-3,-4,-3,-4,-4
 +      !byte -4,-4,-4,-5,-5,-5
 +      !byte -5,-5,-6,-5,-6,-5
 +      !byte -6,-6,-5,-6,-5,-6
 +      !byte -5,-6,-5,-5,-5,-5
 +      !byte -5,-4,-4,-4,-4,-4
 +      !byte -3,-4,-3,-2,-3,-2
 +      !byte -2,-2,-1,-1,-1,-1
 +      !byte 0,0,0,0,0,1
 +      !byte 1,1,1,1,1,2
 +      !byte 2,1,2,2,2,2
 +      !byte 1,2,2,2,1,2
 +      !byte 2,1,2,1,1,1
 +      !byte 1,0,1,0,1,0
 +      !byte 0,-1,0,-1,0,-1
 +      !byte -1,-1,-1,-2,-1,-2
 +      !byte -2,-1,-2,-2,-2,-1
 +      !byte -2,-2,-2,-2,-1,-2
 +      !byte -2,-1,-1,-1,-1,-1
 +      !byte -1,0,0,0,0,0
 +      !byte 1,1,1,1,2,2
 +      !byte 2,3,2,3,4,3
 +      !byte 4,4,4,4,4,5
 +      !byte 5,5,5,5,6,5
 +      !byte 6,5,6,6
 +
 +</code>
  
base/sprite_x-coordinate_calculus.txt ยท Last modified: 2015-04-17 04:34 (external edit)