Help with sprite scaling issue - GameCreators Forum

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Ratty Rat

23

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Joined: 24th Sep 2002

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Posted: 2nd Feb 2011 11:10

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Hi all,
I have got an odd problem when scaling sprites and hope you can help.

In the program I am writing the sprites need to act as wall sections and butt up against each other, scaling can occur and they need to stay right next to each other with no gaps. When scaling up I noticed some gaps appearing, so I wrote the following little program to investigate this:

+ Code Snippet

REM test sprite scaling

sync on

rem build 2 sprites, bas size of 100x100
cls 0x301010
get image 1,0,0,100,100
sprite 1,100,100,1
cls 0x103010
get image 2,0,0,100,100
sprite 2,200,125,2

sync

SCALE# = 1 : lastscale# = 1

do
    cls 0x2020ff
    print SCALE#
    rem scale 
    SCALE# = CLAMP(SCALE# + (MOUSEMOVEZ() / 1000.0),0.16,3.04)
    if SCALE# <> lastscale# 
        sprite 1,100 * SCALE#,100 * SCALE#,1
        sprite 2,200 * SCALE#,125 * SCALE#,2
        size sprite 1,100 * SCALE#,100 * SCALE#
        size sprite 2,100 * SCALE#,100 * SCALE#
        lastscale# = SCALE#
    endif
    if MOUSECLICK() = 1 then delete sprite 1: delete sprite 2 : lastscale# = 0
    sync
loop

Use the scroll wheel to scale up and down, you can click the LMB to delete the sprites.

Notice that at some point while scaling up a gap appears, this is not altogether unexpected and I was working on fixing it when I noticed something odd - when scaling back down again the gap remains, even at scales where no gap appeared before and often even at scale 1 which is back where we started from (and even if the sprites are deleted and recreated).

So I think I have two problems :-
1) can anyone explain why a gap sometimes remains at scale 1?
2) Does anyone have some way of making the sprites continue to show no gap when scaled up?

Thanks for reading,
RR.

"Don`t try to engage my enthusiasm, I don`t have one"

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Quel

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Joined: 13th Mar 2009

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Posted: 2nd Feb 2011 12:39

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Use integer numbers when scaling sprites because floats will pop between two round numbers quite undeterminably...

It's not a limitation you need to do that, because sprites are already limited by pixels, they are not antialiased. At least that i know of.

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Ratty Rat

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Joined: 24th Sep 2002

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Posted: 2nd Feb 2011 13:12

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Thanks Quel, that pushed me in the right direction, below is a revised version that scales using integers, the disturbing thing is what values end up in those integers:

+ Code Snippet

REM test sprite scaling

sync on

rem build 2 sprites, bas size of 100x100
cls 0x301010
get image 1,0,0,100,100
sprite 1,100,100,1
cls 0x103010
get image 2,0,0,100,100
sprite 2,200,125,2

sync

SCALE# = 1 : lastscale# = 0

do
    cls 0x2020ff
    print "Scale = " ,SCALE#," int(Scale) = ",int(SCALE#)
    print "xp1,yp1 = " ,xp1,",",yp1," : xs1,ys1 = ", xs1,",",ys1
    print "xp2,yp2 = " ,xp2,",",yp2," : xs2,ys2 = ", xs2,",",ys2
    rem scale 
    SCALE# = INT(SCALE# * 100.0) / 100.0
    if SCALE# <> lastscale# 
        xp1 = 100 * SCALE# : yp1 = 100 * SCALE#
        xs1 = 100 * SCALE# : ys1 = 100 * SCALE#
        xp2 = 200 * SCALE# : yp2 = 125 * SCALE#
        xs2 = 100 * SCALE# : ys2 = 100 * SCALE#
        sprite 1,xp1,yp1,1
        sprite 2,xp2,yp2,2
        size sprite 1,xs1,ys1
        size sprite 2,xs2,ys2
        lastscale# = SCALE#
    endif
    if MOUSECLICK() = 1 then delete sprite 1: delete sprite 2 : lastscale# = 0
    sync
loop

I noticed here that, when the gap appears at scale 1, although the printed scale shows as 1, doing an int on it gives zero, suggesting it is actually 0.9999999999....

Below is a fix, for this example at least, it keeps the SCALE to 2 decimal places, and resets it to 1 exactly when the scale is passing 1:

REM test sprite scaling

sync on

rem build 2 sprites, bas size of 100x100
cls 0x301010
get image 1,0,0,100,100
sprite 1,100,100,1
cls 0x103010
get image 2,0,0,100,100
sprite 2,200,125,2

sync

SCALE# = 1 : lastscale# = 0

do
    cls 0x2020ff
    print "Scale = " ,SCALE#," int(Scale) = ",int(SCALE#)
    print "xp1,yp1 = " ,xp1,",",yp1," : xs1,ys1 = ", xs1,",",ys1
    print "xp2,yp2 = " ,xp2,",",yp2," : xs2,ys2 = ", xs2,",",ys2
    rem scale 
    SCALE# = CLAMP(SCALE# + (MOUSEMOVEZ() / 1000.0),0.16,3.04) 
    rem fix SCALE# to 2 decimal places
    SCALE# = INT(SCALE# * 100.0) / 100.0
    if SCALE# <> lastscale# 
        rem reset scale to be 1 when it passes the boundary of 1
        if (SCALE# > 1 and lastscale# < 1) or (SCALE# < 1 and lastscale# > 1) then SCALE# = 1
        xp1 = 100 * SCALE# : yp1 = 100 * SCALE#
        xs1 = 100 * SCALE# : ys1 = 100 * SCALE#
        xp2 = 200 * SCALE# : yp2 = 125 * SCALE#
        xs2 = 100 * SCALE# : ys2 = 100 * SCALE#
        sprite 1,xp1,yp1,1
        sprite 2,xp2,yp2,2
        size sprite 1,xs1,ys1
        size sprite 2,xs2,ys2
        lastscale# = SCALE#
    endif
    if MOUSECLICK() = 1 then delete sprite 1: delete sprite 2 : lastscale# = 0
    sync
loop

+ Code Snippet

REM test sprite scaling

sync on

rem build 2 sprites, bas size of 100x100
cls 0x301010
get image 1,0,0,100,100
sprite 1,100,100,1
cls 0x103010
get image 2,0,0,100,100
sprite 2,200,125,2

sync

SCALE# = 1 : lastscale# = 0

do
    cls 0x2020ff
    print "Scale = " ,SCALE#," int(Scale) = ",int(SCALE#)
    print "xp1,yp1 = " ,xp1,",",yp1," : xs1,ys1 = ", xs1,",",ys1
    print "xp2,yp2 = " ,xp2,",",yp2," : xs2,ys2 = ", xs2,",",ys2
    rem scale 
    SCALE# = CLAMP(SCALE# + (MOUSEMOVEZ() / 1000.0),0.16,3.04) 
    rem fix SCALE# to 2 decimal places
    SCALE# = INT(SCALE# * 100.0) / 100.0
    if SCALE# <> lastscale# 
        rem reset scale to be 1 when it passes the boundary of 1
        if (SCALE# > 1 and lastscale# < 1) or (SCALE# < 1 and lastscale# > 1) then SCALE# = 1
        xp1 = 100 * SCALE# : yp1 = 100 * SCALE#
        xs1 = 100 * SCALE# : ys1 = 100 * SCALE#
        xp2 = 200 * SCALE# : yp2 = 125 * SCALE#
        xs2 = 100 * SCALE# : ys2 = 100 * SCALE#
        sprite 1,xp1,yp1,1
        sprite 2,xp2,yp2,2
        size sprite 1,xs1,ys1
        size sprite 2,xs2,ys2
        lastscale# = SCALE#
    endif
    if MOUSECLICK() = 1 then delete sprite 1: delete sprite 2 : lastscale# = 0
    sync
loop

RR

"Don`t try to engage my enthusiasm, I don`t have one"

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