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embedder: fix bit-order in software pixel format description (flutter/engine#57156)

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The order of the components for packed software pixel formats is incorrectly documented as being the order in the native type, least-significant-bit first. In reality it's the other way around. For example, for `RGB565`, the `R` is the 5 most significant bits in the 2-byte pixel value, rather than the least significant bits. The test even verify it is that way:

https://github.com/flutter/engine/blob/main/shell/platform/embedder/tests/embedder_unittests.cc#L2782-L2785

I assume noone used the software pixel formats until @sodiboo did, that's why it's gone unnoticed for so long.

Also contains some other minor documentation improvements.

- Issue: https://github.com/flutter/flutter/issues/160149

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style
This commit is contained in:
Hannes Winkler 2024-12-17 19:09:06 +01:00 committed by GitHub
parent fe7d6f3917
commit 7f8da94c21
1 changed files with 25 additions and 1 deletions
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26
engine/src/flutter/shell/platform/embedder/embedder.h
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@ -352,6 +352,9 @@ typedef enum {
/// r = (p >> 11) & 0x1F;
/// g = (p >> 5) & 0x3F;
/// b = p & 0x1F;
///
/// On most (== little-endian) systems, this is equivalent to wayland format
/// RGB565 (WL_DRM_FORMAT_RGB565, WL_SHM_FORMAT_RGB565).
kFlutterSoftwarePixelFormatRGB565,
/// Pixel with 4 bits each for alpha, red, green, blue; in 16-bit word.
@ -359,6 +362,9 @@ typedef enum {
/// g = (p >> 4) & 0xF;
/// b = p & 0xF;
/// a = (p >> 12) & 0xF;
///
/// On most (== little-endian) systems, this is equivalent to wayland format
/// RGBA4444 (WL_DRM_FORMAT_RGBA4444, WL_SHM_FORMAT_RGBA4444).
kFlutterSoftwarePixelFormatRGBA4444,
/// Pixel with 8 bits each for red, green, blue, alpha.
@ -366,12 +372,18 @@ typedef enum {
/// g = p[1];
/// b = p[2];
/// a = p[3];
///
/// This is equivalent to wayland format ABGR8888 (WL_DRM_FORMAT_ABGR8888,
/// WL_SHM_FORMAT_ABGR8888).
kFlutterSoftwarePixelFormatRGBA8888,
/// Pixel with 8 bits each for red, green and blue and 8 unused bits.
/// r = p[0];
/// g = p[1];
/// b = p[2];
///
/// This is equivalent to wayland format XBGR8888 (WL_DRM_FORMAT_XBGR8888,
/// WL_SHM_FORMAT_XBGR8888).
kFlutterSoftwarePixelFormatRGBX8888,
/// Pixel with 8 bits each for blue, green, red and alpha.
@ -379,6 +391,9 @@ typedef enum {
/// g = p[1];
/// b = p[0];
/// a = p[3];
///
/// This is equivalent to wayland format ARGB8888 (WL_DRM_FORMAT_ARGB8888,
/// WL_SHM_FORMAT_ARGB8888).
kFlutterSoftwarePixelFormatBGRA8888,
/// Either kFlutterSoftwarePixelFormatBGRA8888 or
@ -1741,7 +1756,8 @@ typedef struct {
/// store.
VoidCallback destruction_callback;
/// The pixel format that the engine should use to render into the allocation.
/// In most cases, kR
///
/// On Linux, kFlutterSoftwarePixelFormatBGRA8888 is most commonly used.
FlutterSoftwarePixelFormat pixel_format;
} FlutterSoftwareBackingStore2;
@ -2011,6 +2027,14 @@ typedef struct {
/// The callback should return true if the operation was successful.
FlutterLayersPresentCallback present_layers_callback;
/// Avoid caching backing stores provided by this compositor.
///
/// The engine has an internal backing store cache. Instead of
/// creating & destroying backing stores for every frame, created
/// backing stores are automatically reused for subsequent frames.
///
/// If you wish to change this behavior and destroy backing stores after
/// they've been used once, and create new backing stores for every frame,
/// you can set this bool to true.
bool avoid_backing_store_cache;
/// Callback invoked by the engine to composite the contents of each layer
/// onto the specified view.