[aapt2] Add a compression control option to 'compile'

aapt2 recompresses all PNGs it compiles, and by default it
uses the best (and slowest) zlib compression level, 9.

This change adds a command line option --png-compression-level
to control that, so it's possible to set it to something faster
e.g. 6 which is usually 5x faster and around 101% of the size
of level 9 PNGs

Test: manual, compile Framework
Flag: EXEMPT tool
Change-Id: Ibe5f47b82e1c13be0a4ffff0e07e675871abc956

4 files changed, 24 insertions, 4 deletions

diff --git a/libs/androidfw/PngCrunch.cpp b/libs/androidfw/PngCrunch.cpp
index cf3c0eeff402..e94540544cf5 100644
--- a/libs/androidfw/PngCrunch.cpp
+++ b/libs/androidfw/PngCrunch.cpp
@@ -506,8 +506,7 @@ bool WritePng(const Image* image, const NinePatch* nine_patch, OutputStream* out
   // Set up the write functions which write to our custom data sources.
   png_set_write_fn(write_ptr, (png_voidp)out, WriteDataToStream, nullptr);
 
-  // We want small files and can take the performance hit to achieve this goal.
-  png_set_compression_level(write_ptr, Z_BEST_COMPRESSION);
+  png_set_compression_level(write_ptr, options.compression_level);
 
   // Begin analysis of the image data.
   // Scan the entire image and determine if:
diff --git a/libs/androidfw/include/androidfw/Png.h b/libs/androidfw/include/androidfw/Png.h
index 2ece43e08110..72be59b8f313 100644
--- a/libs/androidfw/include/androidfw/Png.h
+++ b/libs/androidfw/include/androidfw/Png.h
@@ -31,6 +31,8 @@ constexpr size_t kPngSignatureSize = 8u;
 
 struct PngOptions {
   int grayscale_tolerance = 0;
+  // By default we want small files and can take the performance hit to achieve this goal.
+  int compression_level = 9;
 };
 
 /**
diff --git a/tools/aapt2/cmd/Compile.cpp b/tools/aapt2/cmd/Compile.cpp
index 52372fa38525..a5e18d35a256 100644
--- a/tools/aapt2/cmd/Compile.cpp
+++ b/tools/aapt2/cmd/Compile.cpp
@@ -605,8 +605,9 @@ static bool CompilePng(IAaptContext* context, const CompileOptions& options,
     }
 
     // Write the crunched PNG.
-    if (!android::WritePng(image.get(), nine_patch.get(), &crunched_png_buffer_out, {},
-                           &source_diag, context->IsVerbose())) {
+    if (!android::WritePng(image.get(), nine_patch.get(), &crunched_png_buffer_out,
+                           {.compression_level = options.png_compression_level_int}, &source_diag,
+                           context->IsVerbose())) {
       return false;
     }
 
@@ -924,6 +925,19 @@ int CompileCommand::Action(const std::vector<std::string>& args) {
     }
   }
 
+  if (!options_.png_compression_level) {
+    options_.png_compression_level_int = 9;
+  } else {
+    if (options_.png_compression_level->size() != 1 ||
+        options_.png_compression_level->front() < '0' ||
+        options_.png_compression_level->front() > '9') {
+      context.GetDiagnostics()->Error(
+          android::DiagMessage() << "PNG compression level should be a number in [0..9] range");
+      return 1;
+    }
+    options_.png_compression_level_int = options_.png_compression_level->front() - '0';
+  }
+
   return Compile(&context, file_collection.get(), archive_writer.get(), options_);
 }
 
diff --git a/tools/aapt2/cmd/Compile.h b/tools/aapt2/cmd/Compile.h
index 70c8791524c8..e244546476b0 100644
--- a/tools/aapt2/cmd/Compile.h
+++ b/tools/aapt2/cmd/Compile.h
@@ -47,6 +47,8 @@ struct CompileOptions {
   bool verbose = false;
   std::optional<std::string> product_;
   FeatureFlagValues feature_flag_values;
+  std::optional<std::string> png_compression_level;
+  int png_compression_level_int = 9;
 };
 
 /** Parses flags and compiles resources to be used in linking.  */
@@ -65,6 +67,9 @@ class CompileCommand : public Command {
     AddOptionalSwitch("--pseudo-localize", "Generate resources for pseudo-locales "
         "(en-XA and ar-XB)", &options_.pseudolocalize);
     AddOptionalSwitch("--no-crunch", "Disables PNG processing", &options_.no_png_crunch);
+    AddOptionalFlag("--png-compression-level",
+                    "Set the zlib compression level for crunched PNG images, [0-9], 9 by default.",
+                    &options_.png_compression_level);
     AddOptionalSwitch("--legacy", "Treat errors that used to be valid in AAPT as warnings",
         &options_.legacy_mode);
     AddOptionalSwitch("--preserve-visibility-of-styleables",