Uplift — Material shadows on Android

In this session, we'll cover how elevation works on Android. From an overview of the available APIs, seeing what is new in Android P, and getting to the nitty gritty of how shadows are rendered on HWUI and Skia. Lastly, we'll learn how to take advantage of the existing APIs and work within their limitations to obtain original and unique results.

This talk follows the track of existing blog article(s) on the topic: https://blog.usejournal.com/playing-with-elevation-in-android-91af4f3be596 and its two follow-ups. There is also an open source app, Uplift, which will be used to showcase the effects as we talk about them: https://github.com/rock3r/uplift

—

Keynote file and PDF: https://www.dropbox.com/sh/8dwfli2yn8bghjb/AACgTQtOe3SWCDz6Lrb6ZDUia?dl=0
Screen recording available here: https://youtu.be/WQa8NWEeG5Y

Transcript

1. Uplift
   Material shadows
   on Android
   Sebastiano
   Poggi
   @seebrock3r
   JetBrains
   

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2. • Design system
   • Design system system
   • Material Theming
   • Physical metaphor
   • Paper and ink
   • Not skeuomorphism
   Material Design
   

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3. • Magical sheets of material
   • Metaphor of physical paper
   • Fixed shape
   • Any shape, any size
   • React to lights, cast shadows
   What is THE Material?
   

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4. • Material sheets can move around
   • E.g., bottom sheets, FABs, etc
   • They can sometimes change “parent”
   • E.g., shared element transitions
   Meaningful motion
   

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5. • Magical ink on magical paper
   • Content on the sheets is ink
   • Ink has a colour, material is generally white
   • Ink can animate freely on its sheet
   A colourful system
   Lorem ipsum
   Dolor sit amet, consectetur
   adipiscing elit.
   Lorem ipsum, dolor
   sit amet
   

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6. • Everything exists in a physical space
   • Sheets have X and Y coordinates
   • But also a Z
   • The screen “background” is Z = 0
   The environment
   x
   y
   z
   

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7. • Everything exists in a physical space
   • Sheets have X and Y coordinates
   • But also a Z
   • The screen “background” is Z = 0
   • Sheets have Z >= 0
   The environment
   x
   y
   z
   z = 5
   

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8. • The Z coordinate is called elevation
   • android:elevation
   • Elevation is measured in dp
   Elevation
   z
   z = 5dp
   • Animated with translationZ
   translationZ = 3dp
   +
   

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9. Elevation
   z
   z = 5dp
   translationZ = 3dp
   +
   • The Z coordinate is called elevation
   • android:elevation
   • Elevation is measured in dp
   • Animated with translationZ
   

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10. Let there be light
    • There are two lights
    • Positioned in screen coordinates
    • A point light
    • 600dp above the screen, 800dp wide
    

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11. Let there be light
    • There are two lights
    • Positioned in screen coordinates
    • A point light
    • 600dp above the screen, 800dp wide
    • An omnidirectional light
    • At infinite distance above the screen 420dp
    800dp
    

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12. Let there be light
    

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13. Let there be light
    umbra
    penumbra
    vs
    

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14. Let there be light
    umbra
    penumbra
    vs
    

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15. Let there be light
    umbra
    penumbra
    vs
    

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16. Ambient shadow
    Spot shadow
    

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17. Ambient shadow
    Spot shadow
    

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18. Ambient shadow
    Spot shadow
    

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19. Spot shadows movement
    

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20. Spot shadows movement
    

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21. Spot shadows movement
    

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22. Spot shadows movement
    

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23. Spot shadows movement
    The spot shadow “goes down”
    relative to its caster as the Y
    coordinate increases
    

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24. Spot shadows movement
    The spot shadow “goes down”
    relative to its caster as the Y
    coordinate increases
    

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25. • Shadows are always black #000000
    • Shadows are very subtle
    • Ambient shadow is 3.9% opaque
    • Spot shadow is 19% opaque
    • …except on TVs
    • 15% and 30% opaque respectively
    Shadows in Android
    normal
    TV
    

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26. • Android provides one obvious knob: elevation
    • Makes shadow smaller or larger
    • Elevation is the Z coordinate
    • Changes distance from sheet and spotlight
    • Impacts the Y parallax amount
    Controlling the shadow
    

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27. Spot shadows and elevation
    elevation: 2 dp
    *not on scale
    

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28. elevation: 2 dp
    delta:
    *not on scale
    Spot shadows and elevation
    

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29. elevation: 2 dp
    delta:
    elevation: 10 dp
    *not on scale
    Spot shadows and elevation
    

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30. elevation: 2 dp
    delta:
    elevation: 10 dp
    *not on scale
    delta:
    Spot shadows and elevation
    

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31. • Android uses Outline since Lollipop
    • Outlines have a shape and an alpha
    • Outlines provide the shape
    • Shapes used for clipping, and light occlusion
    • …aka shadows
    • Views have ViewOutlineProviders
    Shadow shapes
    

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32. • A number of possible shapes
    • Empty, rounded rects, generic convex paths
    • Rects and ellipses are rounded rects
    • Views get outlines from their background
    Shadow shapes
    

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33. Drawable outlines
    Drawable
    ShapeDrawable
    BitmapDrawable
    • View backgrounds are Drawables
    • Different drawables handle outlines differently
    • The base Drawable has a zero-alpha rect
    • BitmapDrawables have a rect, too
    • Non-zero alpha only if fully opaque
    • ShapeDrawables match their shape
    

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34. Drawable outlines
    Drawable
    ShapeDrawable
    BitmapDrawable
    • LayerDrawable and TransitionDrawable use
    first wrapped bitmap with an outline, if any
    • StateListDrawable and LevelListDrawable
    use “current” outline
    • NinePatchDrawable uses user-defined optical
    bounds, or gets rounded rect from AAPT
    Transition/
    LayerDrawable
    NinePatch
    Drawable
    State/Level
    ListDrawable
    

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35. Drawable outlines
    • InsetDrawable uses the outline of the wrapped
    drawable
    • DrawableWrappers use wrapped drawable
    outline, or the default zero-alpha bounds
    • RotateDrawable, ClipDrawable,
    ScaleDrawable
    Drawable
    ShapeDrawable
    BitmapDrawable
    Transition/
    LayerDrawable
    NinePatch
    Drawable
    Inset
    Drawable
    State/Level
    ListDrawable
    Drawable

    Wrapper
    

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36. • You can swap and tweak outlines
    • Custom ViewOutlineProvider
    • Many possibilities
    • Change shadow shape
    • Shadow size and position
    Manipulating outlines
    

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37. Manipulating outlines
    • You can swap and tweak outlines
    • Custom ViewOutlineProvider
    • Many possibilities
    • Change shadow shape
    • Shadow size and position
    

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38. Manipulating outlines
    • You can swap and tweak outlines
    • Custom ViewOutlineProvider
    • Many possibilities
    • Change shadow shape
    • Shadow size and position
    

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39. Manipulating outlines
    • You can swap and tweak outlines
    • Custom ViewOutlineProvider
    • Many possibilities
    • Change shadow shape
    • Shadow size and position
    

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40. Manipulating outlines
    • You can swap and tweak outlines
    • Custom ViewOutlineProvider
    • Many possibilities
    • Change shadow shape
    • Shadow size and position
    • Look out for rendering artefacts
    

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41. • Material specs don’t impose a shadow colour
    • Shadows are always black in reality
    • There is no way to control the colour either
    • …or at least, not before Pie
    Coloured shadows
    #000000
    

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42. Coloured shadows
    #000000
    #FF0000
    • New APIs in Android Pie (API 28)
    • Set the spot and ambient shadow colours
    • outlineAmbientShadowColor &
    outlineSpotShadowColor
    

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43. Coloured shadows
    #000000
    #FF0000
    • New APIs in Android Pie (API 28)
    • Set the spot and ambient shadow colours
    • outlineAmbientShadowColor &
    outlineSpotShadowColor
    

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44. Coloured shadows
    #000000
    #FF0000
    • New APIs in Android Pie (API 28)
    • Set the spot and ambient shadow colours
    • outlineAmbientShadowColor &
    outlineSpotShadowColor
    • Colours should be opaque
    • But they still kinda look like crap
    

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45. • They look like crap because of low alpha
    • Alpha is controlled by the theme
    • Starting from Lollipop (API 21)
    • ambientShadowAlpha &
    spotShadowAlpha
    • Used to make shadows clearer in TV themes
    Normal TV
    Shadows opacity
    

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46. #000000
    [
    ]
    Shadows opacity
    

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47. [ ]
    600dp
    Light source
    distance
    Shadow colour
    (opaque)
    * =
    Shadow alpha
    (from theme)
    Final shadow
    colour
    (0, 0, 600) 0.19 #FF000000 #30000000
    #FF0000
    #000000
    Shadows opacity
    

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48. Coloured shadows
    [ ]
    600dp
    Light source
    distance
    Shadow colour
    (opaque)
    * =
    Shadow alpha
    (from theme)
    Final shadow
    colour
    (0, 0, 600) 0.19
    #FF0000
    #000000
    #FFFF0000 #30FF0000
    

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49. Colour and opacity
    • “Right” alpha depends on colours
    • Both shadow and background
    

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50. Colour and opacity
    • “Right” alpha depends on colours
    • Both shadow and background
    

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51. Colour and opacity
    • “Right” alpha depends on colours
    • Both shadow and background
    

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52. Colour and opacity
    • “Right” alpha depends on colours
    • Both shadow and background
    

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53. Colour and opacity
    • Theme attributes have a fixed value
    • Cannot change at runtime (no APIs)
    • Applied to all views
    • “Right” alpha depends on colours
    • Both shadow and background
    

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54. • Difficult to have only some coloured shadows
    • Settings for one may not work for others
    Colour and opacity
    Checkout
    Cart
    Shipping & payment
    PURCHASE
    PURCHASE
    123 Fake St, N1 2SA London, UK
    Amex ending in 1234
    $
    Express shipping — FREE
    Delivered the next day
    Broccoli
    In cart: 3
    £ 3.45
    £1.15 each
    Banana
    In cart: 7
    £ 2.59
    £0.37 each
    Total: £ 6.14
    

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55. Colour and opacity
    Checkout
    Cart
    Shipping & payment
    PURCHASE
    PURCHASE
    123 Fake St, N1 2SA London, UK
    Amex ending in 1234
    $
    Express shipping — FREE
    Delivered the next day
    Broccoli
    In cart: 3
    £ 3.45
    £1.15 each
    Banana
    In cart: 7
    £ 2.59
    £0.37 each
    Total: £ 6.14
    • Difficult to have only some coloured shadows
    • Settings for one may not work for others
    

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56. Colour and opacity
    • Difficult to have only some coloured shadows
    • Settings for one may not work for others
    Checkout
    Cart
    Shipping & payment
    PURCHASE
    PURCHASE
    123 Fake St, N1 2SA London, UK
    Amex ending in 1234
    $
    Express shipping — FREE
    Delivered the next day
    Broccoli
    In cart: 3
    £ 3.45
    £1.15 each
    Banana
    In cart: 7
    £ 2.59
    £0.37 each
    Total: £ 6.14
    

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57. Colour and opacity
    Checkout
    Cart
    Shipping & payment
    PURCHASE
    PURCHASE
    123 Fake St, N1 2SA London, UK
    Amex ending in 1234
    $
    Express shipping — FREE
    Delivered the next day
    Broccoli
    In cart: 3
    £ 3.45
    £1.15 each
    Banana
    In cart: 7
    £ 2.59
    £0.37 each
    Total: £ 6.14
    • Difficult to have only some coloured shadows
    • Settings for one may not work for others
    

    View Slide

58. Colour and opacity
    Checkout
    Cart
    Shipping & payment
    PURCHASE
    PURCHASE
    123 Fake St, N1 2SA London, UK
    Amex ending in 1234
    $
    Express shipping — FREE
    Delivered the next day
    Broccoli
    In cart: 3
    £ 3.45
    £1.15 each
    Banana
    In cart: 7
    £ 2.59
    £0.37 each
    Total: £ 6.14
    • Difficult to have only some coloured shadows
    • Settings for one may not work for others
    • You can hack around it
    • Theme overlays may help
    • Most likely not worth the pain
    • There is a Better WayTM
    

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59. Colour and opacity
    • Difficult to have only some coloured shadows
    • Settings for one may not work for others
    • You can hack around it
    • Theme overlays may help
    • Most likely not worth the pain
    • There is a Better WayTM
    

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60. A Better WayTM to do coloured shadows
    • Two factors define the final shadow colour
    • The alpha, set by the theme ambientShadowAlpha and spotShadowAlpha
    • The colour set by outlineAmbientShadowColor and outlineSpotShadowColor
    [ ]
    600dp
    Light source
    distance
    Shadow colour
    (opaque)
    * =
    Shadow alpha
    (from theme)
    Final shadow
    colour
    (0, 0, 600) 0.19 #FF000000 #30000000
    

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61. A Better WayTM to do coloured shadows
    • The theme affects everything
    • A pain to change per-view, no runtime control
    • Easy to get it wrong — themes can be confusing
    [ ]
    600dp
    Light source
    distance
    Shadow colour
    (opaque)
    * =
    Shadow alpha
    (from theme)
    Final shadow
    colour
    (0, 0, 600) 0.19 #FF000000 #30000000
    

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62. A Better WayTM to do coloured shadows
    • Shadow colours are easier to use
    • Only change shadow colours for some views
    • We can also change them at runtime
    [ ]
    600dp
    Light source
    distance
    Shadow colour
    (opaque)
    * =
    Shadow alpha
    (from theme)
    Final shadow
    colour
    (0, 0, 600) 0.19 #FF000000 #30000000
    

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63. A Better WayTM to do coloured shadows
    [ ]
    600dp
    Light source
    distance
    Shadow colour
    (opaque)
    *
    0.19
    1.00
    Shadow alpha
    (from theme)
    =
    #FF000000
    #FFFF0000
    #30000000
    #FFFF0000
    Final shadow
    colour
    (0, 0, 600)
    • Final alpha now fully controlled by colours’ alpha
    • The trick: set the alphas to 1.0
    

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64. A Better WayTM to do coloured shadows
    [ ]
    600dp
    (0, 0, 600)
    Light source
    distance
    Shadow colour
    (opaque)
    *
    1.00
    0.19
    Shadow alpha
    (from theme)
    =
    #FF000000
    #FFFF0000
    #60FF0000
    #30000000
    #FFFF0000
    #60FF0000
    Final shadow
    colour
    • Final alpha now fully controlled by colours’ alpha
    • The trick: set the alphas to 1.0
    

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65. A Better WayTM to do coloured shadows
    [ ]
    600dp
    (0, 0, 600)
    Light source
    distance
    Shadow colour
    (opaque)
    *
    1.00
    Shadow alpha
    (from theme)
    =
    #FFFF0000
    #60FF0000
    #FFFF0000
    #60FF0000
    Final shadow
    colour
    • Final alpha now fully controlled by colours’ alpha
    • The trick: set the alphas to 1.0
    

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66. A Better WayTM to do coloured shadows
    [ ]
    600dp
    (0, 0, 600)
    Light source
    distance
    Shadow colour
    (opaque)
    *
    1.00
    Shadow alpha
    (from theme)
    =
    #FFFF0000
    #60FF0000
    #FFFF0000
    #60FF0000
    Final shadow
    colour
    • Set black with alpha colours as shadow colour in theme
    • #0A000000 for outlineAmbientShadowColor (black, 3.9% alpha)
    • #30000000 for outlineSpotShadowColor (black, 19% alpha)
    

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67. • We only consider API 21+
    • The only knobs are shadow alphas
    • Changing those alone is not useful
    • Things really look weird if you do
    What about pre-P?
    

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68. What about pre-P?
    

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69. What about pre-P?
    • Use resource overrides for theme
    

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70. What about pre-P?
    • Use resource overrides for theme
    • Base theme in res/values
    

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71. What about pre-P?
    • Use resource overrides for theme
    • Base theme in res/values
    • Theme for API 21–27 in res/values
    

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72. What about pre-P?
    • Use resource overrides for theme
    • Base theme in res/values
    • Theme for API 21–27 in res/values
    • Theme for API 28+ in res/values-v28
    

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73. What about pre-P?
    • Use resource overrides for theme
    • Base theme in res/values
    • Theme for API 21–27 in res/values
    • Theme for API 28+ in res/values-v28
    • Only change shadows in API 28+
    

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74. res/values
    res/values-v28
    What about pre-P?
    • Use resource overrides for theme
    • Base theme in res/values
    • Theme for API 21–27 in res/values
    • Theme for API 28+ in res/values-v28
    • Only change shadows in API 28+
    

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75. Tying it all together
    

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76. Tying it all together
    

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77. Tying it all together
    

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78. Tying it all together
    

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79. Tying it all together
    Search “uplift”
    

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80. One more thing…
    • Now we control all elevation shadows
    • [Insert maniacal laughter]
    • Can colour just some shadows
    • Or you can animate them
    • Animate translationZ (elevation)
    • Animate the colour/alpha
    

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81. Don’t try this at home
    • The ultimate hack: move the spotlight
    • Cannot move the ambient light
    • LITERALLY no good reason to move them
    • But we like having fun!
    

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82. Don’t try this at home
    • The ultimate hack: move the spotlight
    • Cannot move the ambient light
    • LITERALLY no good reason to move them
    • But we like having fun!
    

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83. Don’t try this at home
    • Use private theme attributes
    • Set *android:lightY
    • Asterisk bypasses AAPT validation
    • SERIOUSLY THOUGH — do not do this, ever!
    • It can break at any time
    • You cannot get anything good out of this
    

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84. Don’t try this at home
    • Use private theme attributes
    • Set *android:lightY
    • Asterisk bypasses AAPT validation
    • SERIOUSLY THOUGH — do not do this, ever!
    • It can break at any time
    • You cannot get anything good out of this
    DO NOT TRY
    THIS AT HOME
    

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85. THANK
    YOU
    

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86. Uplift
    Material shadows
    on Android
    Sebastiano Poggi
    @seebrock3r JetBrains
    Slides at: bit.ly/uplift-slides
    

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