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Fix incorrect view flattening when using a specific not fully transparent color (facebook#51379)
Summary:
Changelog: [General][Fixed] Fix incorrect flattening / non-rendering of views with backgroundColor set to `rgba(255, 255, 255, 127/256)`
Fixesfacebook#51378.
## Context
When testing some unrelated things with Fantom is realized that the color for some text that I wasn't explicitly defining was being set to `rgba(255, 255, 255, 127)`, like here:
https://github.com/facebook/react-native/blob/249a24ac756275eadbe3b4df1ff9c974af1671d2/packages/react-native-fantom/src/__tests__/Fantom-itest.js#L540-L542
When digging a bit more about why, I realized that was actually the value for `UndefinedColor`. When looking a bit deeper, I saw that the value for that constant was being set like this:
```
using Color = int32_t;
namespace HostPlatformColor {
static const facebook::react::Color UndefinedColor =
std::numeric_limits<facebook::react::Color>::max();
}
```
I'm not sure what the logic could've been here:
- Defining it as a value out of bounds for all valid colors? In this case, it's a 32 bit value so all the range of values are actually valid RGBA colors.
- Defining it as a fully opaque white? Seems dangerous for a default because you wouldn't be able to distinguish a explicitly set white color from a non-set color, relevant if you're seeing a white background color in a view on top of another view with any other background color.
The result of this existing logic was actually setting `UndefinedColor` to `rgba(255, 255, 255, 127)` because the alpha channel is defined in the first bits of the value, and `Color` being a signed int with 32 bits, the largest value is `01111....1`, so extracting the first 8 bits, you get 127.
## Changes
This changes the value set for the `UndefinedColor` constant (which is used, among other things, to determine if a view sets a background color, or otherwise could potentially be flattened).
The new value, instead of white with a 127/256 opacity, is back with 0% opacity (or simply the number 0 in `int32_t`).
Differential Revision: D74869311
Copy file name to clipboardExpand all lines: packages/react-native/ReactCommon/react/renderer/graphics/platform/cxx/react/renderer/graphics/HostPlatformColor.h
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