Trevor Merritt
e29ac45c84
scroll left and right work in stdef and hidef adds octo test roms adds schip fonts to memory
105 lines
2.4 KiB
Plaintext
105 lines
2.4 KiB
Plaintext
###########################################
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#
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# Vertical Clip
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#
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# Sprite drawing routines which are capable
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# of clipping a sprite along the top and
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# bottom edges of the screen.
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#
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# These routines are designed with 'lores'
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# 64x32 pixel graphics in mind.
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#
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# Sprite y coordinates must range between
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# 17 and 64- at either extreme the sprite
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# is completely invisible. If only a partial
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# clip along one edge is necessary or
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# other constraints can be added these
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# routines could be simplified.
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#
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###########################################
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:const HEIGHT 15 # sprite height
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:const N_EDGE 32
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:calc N_LIMIT { N_EDGE - HEIGHT }
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:const S_EDGE 64
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:calc S_LIMIT { S_EDGE - HEIGHT }
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:alias offset vd # could be a temp register
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:alias height vc # could be a temp register
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:alias y vb
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:alias x va
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: flower
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0x3C 0x66 0x57 0xB7 0xFB 0x7A 0x1A
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0xC4 0x64 0x79 0x12 0x26 0x2C 0x10 0x08
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: draw-sprite
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# If our sprite is below the north edge,
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# we don't need to perform top clipping:
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if y >= N_EDGE then jump clip-s
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# Calculate the number of pixels we should
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# draw and the corresponding offset into
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# the sprite data which should be used:
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offset := N_EDGE
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offset -= y
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height := HEIGHT
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height -= offset
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# If we're entirely off the top edge,
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# we don't need to draw anything:
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if height == 0 then return
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# Overwrite the lowest nybble of the 'sprite instruction
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# to reflect the desired height:
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v0 := height
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i := nrows
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save v0
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v0 := 0
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i := flower
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i += offset
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:next nrows sprite x v0 HEIGHT
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;
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: clip-s
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# Calculate the number of pixels we
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# should draw based on the height of the screen:
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height := S_EDGE
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height -= y
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# Drawing a 0-height sprite has the unintended
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# consequence of drawing a SuperChip 16x16 sprite,
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# so we must break if the sprite is fully offscreen:
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if height == 0 then return
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# On the other hand, if we're far enough away from the
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# bottom edge we should display the full sprite.
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# We could skip this step if the sprite was always
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# against the bottom edge:
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if y < S_LIMIT then height := HEIGHT
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# Overwrite the lowest nybble of the 'sprite' instruction
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# to parameterize the sprite height on the fly.
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# We must also preserve the y register setting, but
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# that is known statically:
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v0 := 0xB0
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v0 += height
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i := srows
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save v0
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i := flower
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:next srows sprite x y HEIGHT
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;
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: main
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x := 28
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y := 32
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loop
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clear
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draw-sprite
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v0 := key
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if v0 == 5 then y += -1
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if v0 == 8 then y += 1
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again
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