51 lines
1.6 KiB
ArmAsm
51 lines
1.6 KiB
ArmAsm
; Animation helpers
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;
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; These provide animation sequencing and pathing support for animations. Some function are
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; sprite-specific, but the functions are generally applicable to any kind of animation support
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; by the engine, such as swapping tiles or even just having an asynchronous method of updating
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; game data.
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;
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; Depends on the Timers and Script sub-systems
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; AnimatePath
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;
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; Moves a sprite between two keyframe point over a specificed number of steps
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;
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; X = YYXX ; start position
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; A = YYXX ; end position
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; Y = duration ; number of steps from start to end (must be > 0)
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AnimatePath
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pha ; Store the starting point
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and #$00FF
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sta AnimX0
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pla
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xba
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and #$00FF
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sta AnimY0
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txa ; Store the ending point
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and #$00FF
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sta AnimX1
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txa
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xba
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and #$00FF
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sta AnimY1
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sty AnimDuration
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; Calculate the steps for the X and Y positions. This is line drawing two lines
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; at a time . The slope of the lines are (X1 - X0) / Duration and (Y1 - Y0) / Duration.
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;
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; The tricky bit is that we *always* single-step in the "Y" direction (duration), so we
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; actually need to use two differenct algorithms.
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;
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; If |X1 - X0| <= Duration, use a standard Bresenham's
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; If |X1 - X0| > Duration, use the Run-Length Slice algorithm (https://www.phatcode.net/res/224/files/html/ch36/36-02.html)
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lda AnimX1
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lda AnimY
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cmp AnimDuration ; Handle the two cases
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