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How do I skew a Sprite? [bug?] — Gideros Forum
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    How do I skew a Sprite? [bug?]

    piepie Member
    edited August 2015 in General questions
    I'd like to apply a transformation to a sprite like in the attached image: from 1 to 2.

    I tried using Sprite:setSkew from GiderosCodingEasy and using Matrix with the first example from the reference manual, but I couldn't skew my sprite.

    I'd say both methods give the same result:
    it seems that I can only rotate the sprite of the given angle using setSkewY, while setSkewX seems to apply just a slight scaling.

    http://docs.giderosmobile.com/reference/gideros/Matrix
    local angle = math.rad(30)
-- create skew matrix
local m = Matrix.new(1, math.tan(angle), math.tan(angle), 1, 0, 0)
--aply to Sprite
local sprite = Sprite.new()
sprite:setMatrix(m)

    Thank you
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    Comments

    • totebototebo Member
      I noticed skewing has changed in the latest updates. The skew still worked, but the skew itself was more pronounced than before in my tests. In my case it made sense to simply stop using it, but an explanation would be cool for future reference.
      My Gideros games: www.totebo.com
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    • piepie Member
      I don't know if I am doing something wrong or if there is some bug; I am almost sure I tried skew in the past and it was working. Can you still skew sprites?

      Thanks
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    • piepie Member
      edited August 2015
      I tried skewing sprites with both methods on 2014.10 and it works:

      @hgy29 could this be a bug coming from your matrix updates or do we have to use different parameters/approach? (if this is the case the reference manual needs to be updated too :) )

      Thank you

      [edit: 2015.06.30 is the latest release where matrix skew works, but GiderosCodingEasy Sprite:setSkew just rotates the sprite ]
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    • hgy29hgy29 Maintainer
      @pie, I will have a look. There have been a few versions between 2015.03.26 and some other release which had issues with user matrices. I thought it was fixed, but may be wrong..
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    • piepie Member
      Thank you @hgy29

      In 2015.06.30 matrix skew seems to be working, if this could help. :)
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    • hgy29hgy29 Maintainer
      In fact the fix we did was not enough to handle skew. I fixed it in a better way now: https://github.com/gideros/gideros/commit/4698c98c14ce6d60d03c4b7b30e17a579219534f

      It will be in next release.
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    • piepie Member
      Great! Thank you :)
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    • totebototebo Member
      edited April 2016
      Can I confirm that skewing a sprite is no longer working/supported? When skew a sprite in 2016-04 it's only rotated, like @pie mentioned above for an older version.

      This is the code I'm using:
      local shape = Shape.new()
shape:setFillStyle(Shape.SOLID, 0xff0000, 1)
shape:beginPath()
shape:moveTo(0,0)
shape:lineTo(100, 0)
shape:lineTo(100, 200)
shape:lineTo(0, 200)
shape:lineTo(0, 0)
shape:endPath()
shape:setPosition(150, 650)
shape:setSkewY(10)
stage:addChild(shape)
      Using these helper functions:
      https://github.com/ar2rsawseen/GiderosCodingEasy/blob/master/GiderosCodingEasy.lua#L627

      Test project is attached.
      zip
      zip
      Skew.zip
      11K
      Screen Shot 2016-04-20 at 13.42.00.png
      660 x 1202 - 45K
      My Gideros games: www.totebo.com
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    • piepie Member
      edited April 2016
      @totebo as a workaround skewing with Matrix works for me :)
      Matrix.new(1, math.tan(skewangleY), math.tan(skewangleX), 1, 0, 0)
      try
      local angle = math.rad(30)
-- create skew matrix
local m = Matrix.new(1, 0, math.tan(angle), 1, 0, 0) 
--apply to Sprite
shape:setMatrix(m)
      I agree that gideroscodingeasy needs some cleaning/updating, but most of the helper functions still works :)
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    • totebototebo Member
      I am trying to skew a game world, containing hundreds of sprites. So Matrix probably won't work for me in this case.
      My Gideros games: www.totebo.com
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    • hgy29hgy29 Maintainer
      @totebo, why wouldn't it work ? The Matrix will get applied to children Sprites as well...

      Likes: pie

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    • piepie Member
      @totebo I just tried on my game world: as long as you apply the matrix to a sprite (ie. "scene") it works :)
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    • tkhnomantkhnoman Member
      edited April 2016
      I think i remembered this case, since 3D introduced, matrix for skew somehow won't work anymore.
      Probably it would work if frustum is 0.
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    • totebototebo Member
      @hgy29, did you try out the example project I attached? I can't get it to work for some reason.
      My Gideros games: www.totebo.com
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    • hgy29hgy29 Maintainer
      @totebo, just tried and it doesn't work because GCE calls setRotation after calling setMatrix, ruining the setMatrix.

      Let me explain what happens under the hood: gideros sprites use position, scale, rotation and anchorPosition coordinates internally to build a transform matrix, which means that when you give the matrix directly, gideros has to compute position, rotation and translation from it, in case you'd like to query one of these parameters afterwise. If you do setRotation or setScale afterwise, the matrix previously set will be replaced by a new scale,rotate,translate matrix, thus you lose skew or other effects.

      Notre that you can do setPosition freely, because when just translating only the translate part of the matrix is updated.
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