From 24376e7759163ee80ff11065fe4a79ecb0796145 Mon Sep 17 00:00:00 2001
From: Gunnar Beutner <gbeutner@serenityos.org>
Date: Sat, 15 May 2021 15:01:38 +0200
Subject: [PATCH] LibGfx: Avoid copying ByteBuffers while loading PNG images

This wasn't much of a problem before because copying the ByteBuffer
merely copied the RefPtr but now that ByteBuffer behaves like Vector
this causes unnecessary allocations.
---
 Userland/Libraries/LibGfx/PNGLoader.cpp | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/Userland/Libraries/LibGfx/PNGLoader.cpp b/Userland/Libraries/LibGfx/PNGLoader.cpp
index 2e866ffb8b..31d62d9e5d 100644
--- a/Userland/Libraries/LibGfx/PNGLoader.cpp
+++ b/Userland/Libraries/LibGfx/PNGLoader.cpp
@@ -101,7 +101,7 @@ struct PNGLoadingContext {
     bool has_alpha() const { return color_type & 4 || palette_transparency_data.size() > 0; }
     Vector<Scanline> scanlines;
     RefPtr<Gfx::Bitmap> bitmap;
-    ByteBuffer decompression_buffer;
+    ByteBuffer* decompression_buffer { nullptr };
     Vector<u8> compressed_data;
     Vector<PaletteEntry> palette_data;
     Vector<u8> palette_transparency_data;
@@ -580,7 +580,7 @@ static bool decode_png_chunks(PNGLoadingContext& context)
 
 static bool decode_png_bitmap_simple(PNGLoadingContext& context)
 {
-    Streamer streamer(context.decompression_buffer.data(), context.decompression_buffer.size());
+    Streamer streamer(context.decompression_buffer->data(), context.decompression_buffer->size());
 
     for (int y = 0; y < context.height; ++y) {
         u8 filter;
@@ -726,7 +726,7 @@ static bool decode_adam7_pass(PNGLoadingContext& context, Streamer& streamer, in
 
 static bool decode_png_adam7(PNGLoadingContext& context)
 {
-    Streamer streamer(context.decompression_buffer.data(), context.decompression_buffer.size());
+    Streamer streamer(context.decompression_buffer->data(), context.decompression_buffer->size());
     context.bitmap = Bitmap::create_purgeable(context.has_alpha() ? BitmapFormat::BGRA8888 : BitmapFormat::BGRx8888, { context.width, context.height });
     if (!context.bitmap)
         return false;
@@ -759,7 +759,7 @@ static bool decode_png_bitmap(PNGLoadingContext& context)
         context.state = PNGLoadingContext::State::Error;
         return false;
     }
-    context.decompression_buffer = result.value();
+    context.decompression_buffer = &result.value();
     context.compressed_data.clear();
 
     context.scanlines.ensure_capacity(context.height);
@@ -777,7 +777,7 @@ static bool decode_png_bitmap(PNGLoadingContext& context)
         return false;
     }
 
-    context.decompression_buffer.clear();
+    context.decompression_buffer = nullptr;
 
     context.state = PNGLoadingContext::State::BitmapDecoded;
     return true;