====== Shadows: Rule 5 - The Contrast Wall  ======

This is a visibility rule ... **"If a shadow isn't seen ... there is a //contrast wall//!"**

In the Android rendering engine, shadows are not solid objects; but instead are mathematical blurs applied to the background. For a shadow to be visible, there must be a significant difference in brightness (Value) between the shadow and the wallpaper.

==== The Luminance Floor ====
The "eye" recognizes brightness as the subjective value of a measure of luminance. 
On dark backgrounds (a luminance value < 20%, such as OLED black), low-alpha shadows effectively "sink" into the darkness and disappear. The "eye" does not register them.
  * **The Problem:** When a light color is spread over a large radius, the "Luminance Density" drops. A 20% white shadow spread over a 50px radius becomes so thin it is invisible to the human eye.
{{  :section:section-shadow-rule5-luminance_floor.webp?direct&400  }}
  * **The Solution:** To stay visible on dark themes, use a **Higher Alpha** (80%+) or **Solid Colors**. 

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==== Alpha Visualized ====
Shown here are reference characters of the Alpha's for "AA"RRGGBB:
{{  :section:section-shadow-alpha-80_100.webp?direct&500  }}
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{{:ui:ui-color-hex-alpha_values.webp?200}}
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^  Alpha cheat sheet\\ (most useful values)  ^^^
^  Color Picker\\ Hex: FB00FA37\\ {{:ui:ui-color-hex-alpha_values-base_fb00fa37.webp?50}}  ^^^
|  Alpha  |  Transparency  |  Glass Effect  |
|  FF  |  100% opaque  |  Solid  |
|  E6  |  90%  |   ::: |
|  CC  |  80%  |  Almost solid  |
|  B3  |  70%  |  :::  |
|  99  |  60%  |  :::  |
|  80  |  50%  |  Heavy glass  |
|  66  |  40%  |  :::  |
|  4D  |  30%  |  Medium glass  |
|  33  |  20%  |  Light glass  |
|  1A  |  10%  |  Very light glass  |
|  00  |  0% transparent  |
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</WRAP>
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==== Alpha Test Results ====
The images below show shadows (or lack of a shadow) when using the noted shadow options in the launcher's shadow dialog:
{{:section:section-shadow_controlled_tests_1_-_7.webp?direct&200  }}
{{:section:section-shadow_test_parameters.webp?direct&700  }}
\\ \\ \\ 
\\ 
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==== Shadow Contrast Summary ====
{{tablelayout?colwidth="150px,150px,150px,150"&rowsHeaderSource=auto&float=center}}
^  **Summary:**  ^^^^
^ Background Type ^ Shadow Strategy ^ Recommended Alpha ^ Result ^
| **Light Wallpaper** | Dark/Black Shadow | 20% – 50% (`40` to `80`) | **Success:** Soft, realistic depth. |
| **Dark Wallpaper** | White/Light Glow | 80% – 100% (`CC` to `FF`) | **Success:** A visible "Halo" or "Ambient Lift." |
| **Dark Wallpaper** | Any Shadow Color | Below 50% (`80`) | **FAILURE:** Shadow vanishes into the background noise. See [[:howto:howto-shadows-dark_background|this hack]] to overcome the failure. |
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