Add configuration to support compiling engine with SUPPORT_FRACTIONAL_TRANSLATION (#33393)

Author: Jonah Williams

common/config.gni

@@ -22,6 +22,9 @@ declare_args() {
 
   # Whether to use a prebuilt Dart SDK instead of building one.
   flutter_prebuilt_dart_sdk = false
+
+  # Whether layers can be drawn at half pixel boundaries.
+  support_fractional_translation = false
 }
 
 # feature_defines_list ---------------------------------------------------------
@@ -56,6 +59,10 @@ if (flutter_runtime_mode == "debug") {
   feature_defines_list += [ "FLUTTER_RUNTIME_MODE=0" ]
 }
 
+if (support_fractional_translation) {
+  feature_defines_list += [ "SUPPORT_FRACTIONAL_TRANSLATION=1" ]
+}
+
 if (is_ios || is_mac) {
   flutter_cflags_objc = [
     "-Werror=overriding-method-mismatch",

shell/testing/BUILD.gn

@@ -58,10 +58,7 @@ executable("testing_fractional_translation") {
     ]
   }
 
-  defines = [
-    "SUPPORT_FRACTIONAL_TRANSLATION=1",
-    "DISABLE_SOFTWARE_RASTER_CACHE=1",
-  ]
+  defines = []
 
   deps = [
     "//flutter/assets",

shell/testing/tester_main.cc

@@ -68,10 +68,10 @@ class TesterGPUSurfaceSoftware : public GPUSurfaceSoftware {
                            bool render_to_surface)
       : GPUSurfaceSoftware(delegate, render_to_surface) {}
 
-#if DISABLE_SOFTWARE_RASTER_CACHE
+#if SUPPORT_FRACTIONAL_TRANSLATION
   // |Surface|
   bool EnableRasterCache() const override { return false; }
-#endif  // DISABLE_SOFTWARE_RASTER_CACHE
+#endif  // SUPPORT_FRACTIONAL_TRANSLATION
 };
 
 class TesterPlatformView : public PlatformView,

tools/gn

@@ -55,6 +55,9 @@ def get_out_dir(args):
     if args.target_os == 'fuchsia' and args.fuchsia_cpu is not None:
       target_dir.append(args.fuchsia_cpu)
 
+    if args.support_fractional_translation:
+      target_dir.append('fractional')
+
     # This exists for backwards compatibility of tests that are being run
     # on LUCI. This can be removed in coordination with a LUCI change:
     # https://github.com/flutter/flutter/issues/76547
@@ -312,10 +315,10 @@ def to_gn_args(args):
       if runtime_mode == 'debug':
           gn_args['dart_runtime_mode'] = 'develop'
       elif runtime_mode == 'jit_release':
-          gn_args['dart_runtime_mode'] = 'release';
+          gn_args['dart_runtime_mode'] = 'release'
       else:
           gn_args['dart_runtime_mode'] = runtime_mode
-      
+
       # Desktop embeddings can have more dependencies than the engine library,
       # which can be problematic in some build environments (e.g., building on
       # Linux will bring in pkg-config dependencies at generation time). These
@@ -330,6 +333,9 @@ def to_gn_args(args):
     if args.allow_deprecated_api_calls:
       gn_args['allow_deprecated_api_calls'] = args.allow_deprecated_api_calls
 
+    if args.support_fractional_translation:
+      gn_args['support_fractional_translation'] = args.support_fractional_translation
+
     # DBC is not supported anymore.
     if args.interpreter:
       raise Exception('--interpreter is no longer needed on any supported platform.')
@@ -440,7 +446,7 @@ def to_gn_args(args):
       # dart_platform_sdk=True means exclude web-related files, e.g. dart2js,
       # dartdevc, web SDK kernel and source files.
       gn_args['dart_platform_sdk'] = not args.full_dart_sdk
-    
+
     if args.build_glfw_shell is not None:
       gn_args['build_glfw_shell'] = args.build_glfw_shell
 
@@ -613,6 +619,10 @@ def parse_args(args):
 
   parser.add_argument('--fuchsia-target-api-level', dest='fuchsia_target_api_level')
 
+  parser.add_argument('--support-fractional-translation', dest='support_fractional_translation', default=False,
+                      action='store_true', help='Whether to allow layers to render at fraction pixel '
+                      'boundaries.')
+
   # Flags for Dart features.
   parser.add_argument('--use-mallinfo2', dest='use_mallinfo2', default=False, action='store_true',
                       help='Use mallinfo2 to collect malloc stats.')