Adds support for f16 surfaces to wide gamut unit tests. (#126712)

issue: flutter/flutter#126620

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Author: gaaclarke

dev/integration_tests/wide_gamut_test/integration_test/app_test.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:math' as math;
 import 'dart:typed_data';
 
 import 'package:flutter/services.dart';
@@ -19,12 +20,49 @@ double _decodeBGR10(int x) {
   return (x * slope) + intercept;
 }
 
+double _decodeHalf(int x) {
+  if (x == 0x7c00) {
+    return double.infinity;
+  }
+  if (x == 0xfc00) {
+    return -double.infinity;
+  }
+  final double sign = x & 0x8000 == 0 ? 1.0 : -1.0;
+  final int exponent = (x >> 10) & 0x1f;
+  final int fraction = x & 0x3ff;
+  if (exponent == 0) {
+    return sign * math.pow(2.0, -14) * (fraction / 1024.0);
+  } else {
+    return sign * math.pow(2.0, exponent - 15) * (1.0 + fraction / 1024.0);
+  }
+}
+
 bool _isAlmost(double x, double y, double epsilon) {
   return (x - y).abs() < epsilon;
 }
 
 List<double> _deepRed = <double>[1.0931, -0.2268, -0.1501];
 
+bool _findRGBAF16Color(
+    Uint8List bytes, int width, int height, List<double> color) {
+  final ByteData byteData = ByteData.sublistView(bytes);
+  expect(bytes.lengthInBytes, width * height * 8);
+  expect(bytes.lengthInBytes, byteData.lengthInBytes);
+  bool foundDeepRed = false;
+  for (int i = 0; i < bytes.lengthInBytes; i += 8) {
+    final int pixel = byteData.getUint64(i, Endian.host);
+    final double blue = _decodeHalf((pixel >> 32) & 0xffff);
+    final double green = _decodeHalf((pixel >> 16) & 0xffff);
+    final double red = _decodeHalf((pixel >> 0) & 0xffff);
+    if (_isAlmost(red, color[0], 0.01) &&
+        _isAlmost(green, color[1], 0.01) &&
+        _isAlmost(blue, color[2], 0.01)) {
+      foundDeepRed = true;
+    }
+  }
+  return foundDeepRed;
+}
+
 bool _findBGRA10Color(
     Uint8List bytes, int width, int height, List<double> color) {
   final ByteData byteData = ByteData.sublistView(bytes);
@@ -75,6 +113,8 @@ bool _findColor(List<Object?> result, List<double> color) {
     return _findBGR10Color((result[3] as Uint8List?)!, width, height, color);
   } else if (format == 'MTLPixelFormatBGRA10_XR') {
     return _findBGRA10Color((result[3] as Uint8List?)!, width, height, color);
+  } else if (format == 'MTLPixelFormatRGBA16Float') {
+    return _findRGBAF16Color((result[3] as Uint8List?)!, width, height, color);
   } else {
     fail('Unsupported pixel format: $format');
   }