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Uplift Material shadows on Android Sebastiano Poggi @seebrock3r JetBrains

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

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• 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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• 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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• 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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• 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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• 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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• 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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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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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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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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Let there be light

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Let there be light umbra penumbra vs

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Let there be light umbra penumbra vs

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Let there be light umbra penumbra vs

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Ambient shadow Spot shadow

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Ambient shadow Spot shadow

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Ambient shadow Spot shadow

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Spot shadows movement

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Spot shadows movement

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Spot shadows movement

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Spot shadows movement

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

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

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• 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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• 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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Spot shadows and elevation elevation: 2 dp *not on scale

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

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

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

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

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

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

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

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

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

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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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• 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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#000000 [ ] Shadows opacity

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[ ] 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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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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Colour and opacity • “Right” alpha depends on colours • Both shadow and background

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

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

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

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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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• 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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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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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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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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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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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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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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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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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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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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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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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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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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• 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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What about pre-P?

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

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

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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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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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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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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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Tying it all together

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Tying it all together

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Tying it all together

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Tying it all together

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Tying it all together Search “uplift”

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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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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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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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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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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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THANK YOU

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