LibDraw: Add ImageLoader, a simple abstraction for image loading

An ImageLoader is a generic interface for loading encoded image data of
any supported format. It has an ImageLoaderPlugin internally that does
all the work.

This patch adds an initial PNGImageLoaderPlugin that knows how to
retrieve the size of a PNG, and the bitmap. The API is divided into
size() and bitmap() to facilitate geometry-only decoding.
This will be useful in places like LibHTML where we need dimensions for
layout purposes but can wait with the bitmap until later.

Libraries/LibDraw/PNGLoader.cpp

@@ -61,6 +61,14 @@ struct [[gnu::packed]] Quad16
 };
 
 struct PNGLoadingContext {
+    enum class State {
+        NotDecoded,
+        ChunksDecoded,
+        BitmapDecoded,
+    };
+    State state { State::NotDecoded };
+    const u8* data { nullptr };
+    size_t data_size { 0 };
     int width { -1 };
     int height { -1 };
     u8 bit_depth { 0 };
@@ -382,23 +390,22 @@ template<bool has_alpha, u8 filter_type>
     }
 }
 
-static RefPtr<GraphicsBitmap> load_png_impl(const u8* data, int data_size)
+static bool decode_png_chunks(PNGLoadingContext& context)
 {
+    ASSERT(context.state == PNGLoadingContext::State::NotDecoded);
 #ifdef PNG_STOPWATCH_DEBUG
     Stopwatch sw("load_png_impl: total");
 #endif
-    const u8* data_ptr = data;
-    int data_remaining = data_size;
+    const u8* data_ptr = context.data;
+    int data_remaining = context.data_size;
 
     const u8 png_header[8] = { 0x89, 'P', 'N', 'G', 13, 10, 26, 10 };
-    if (memcmp(data, png_header, sizeof(png_header))) {
+    if (memcmp(context.data, png_header, sizeof(png_header))) {
         dbgprintf("Invalid PNG header\n");
-        return nullptr;
+        return false;
     }
 
-    PNGLoadingContext context;
-
-    context.compressed_data.ensure_capacity(data_size);
+    context.compressed_data.ensure_capacity(context.data_size);
 
     data_ptr += sizeof(png_header);
     data_remaining -= sizeof(png_header);
@@ -410,11 +417,18 @@ static RefPtr<GraphicsBitmap> load_png_impl(const u8* data, int data_size)
         Streamer streamer(data_ptr, data_remaining);
         while (!streamer.at_end()) {
             if (!process_chunk(streamer, context)) {
-                return nullptr;
+                return false;
             }
         }
     }
 
+    context.state = PNGLoadingContext::State::ChunksDecoded;
+    return true;
+}
+
+static bool decode_png_bitmap(PNGLoadingContext& context)
+{
+    ASSERT(context.state == PNGLoadingContext::State::ChunksDecoded);
     {
 #ifdef PNG_STOPWATCH_DEBUG
         Stopwatch sw("load_png_impl: uncompress");
@@ -423,7 +437,7 @@ static RefPtr<GraphicsBitmap> load_png_impl(const u8* data, int data_size)
         unsigned long destlen = context.decompression_buffer_size;
         int ret = puff(context.decompression_buffer, &destlen, context.compressed_data.data() + 2, &srclen);
         if (ret < 0)
-            return nullptr;
+            return false;
         context.compressed_data.clear();
     }
 
@@ -436,12 +450,12 @@ static RefPtr<GraphicsBitmap> load_png_impl(const u8* data, int data_size)
         for (int y = 0; y < context.height; ++y) {
             u8 filter;
             if (!streamer.read(filter))
-                return nullptr;
+                return false;
 
             context.scanlines.append({ filter });
             auto& scanline_buffer = context.scanlines.last().data;
             if (!streamer.wrap_bytes(scanline_buffer, context.width * context.bytes_per_pixel))
-                return nullptr;
+                return false;
         }
     }
 
@@ -458,6 +472,22 @@ static RefPtr<GraphicsBitmap> load_png_impl(const u8* data, int data_size)
     context.decompression_buffer = nullptr;
     context.decompression_buffer_size = 0;
 
+    context.state = PNGLoadingContext::State::BitmapDecoded;
+    return true;
+}
+
+static RefPtr<GraphicsBitmap> load_png_impl(const u8* data, int data_size)
+{
+    PNGLoadingContext context;
+    context.data = data;
+    context.data_size = data_size;
+
+    if (!decode_png_chunks(context))
+        return nullptr;
+
+    if (!decode_png_bitmap(context))
+        return nullptr;
+
     return context.bitmap;
 }
 
@@ -576,3 +606,37 @@ static bool process_chunk(Streamer& streamer, PNGLoadingContext& context)
         return process_tRNS(chunk_data, context);
     return true;
 }
+
+PNGImageLoaderPlugin::PNGImageLoaderPlugin(const u8* data, size_t size)
+{
+    m_context = make<PNGLoadingContext>();
+    m_context->data = data;
+    m_context->data_size = size;
+}
+
+PNGImageLoaderPlugin::~PNGImageLoaderPlugin()
+{
+}
+
+Size PNGImageLoaderPlugin::size()
+{
+    if (m_context->state == PNGLoadingContext::State::NotDecoded) {
+        bool success = decode_png_chunks(*m_context);
+        ASSERT(success);
+    }
+
+    return { m_context->width, m_context->height };
+}
+
+RefPtr<GraphicsBitmap> PNGImageLoaderPlugin::bitmap()
+{
+    if (m_context->state != PNGLoadingContext::State::BitmapDecoded) {
+        // NOTE: This forces the chunk decoding to happen.
+        size();
+        bool success = decode_png_bitmap(*m_context);
+        ASSERT(success);
+    }
+
+    ASSERT(m_context->bitmap);
+    return m_context->bitmap;
+}