From b2a559ddb075fbdf75fe3642b5d296616a675665 Mon Sep 17 00:00:00 2001
From: Lucas CHOLLET <lucas.chollet@free.fr>
Date: Fri, 28 Jul 2023 22:09:55 -0400
Subject: [PATCH] LibGfx/JPEGXL: Create `Image` with the correct number of
 channel

As a quick and dirty implementation, we used to assume that the final
image was always composed of three channels of the same size. However,
JPEG XL has support for more than three channels and extra channels can
have a smaller size. With this patch, we now create the image with the
correct number of channel and with their respective sizes.
---
 .../LibGfx/ImageFormats/JPEGXLLoader.cpp      | 28 +++++++++++++++----
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/Userland/Libraries/LibGfx/ImageFormats/JPEGXLLoader.cpp b/Userland/Libraries/LibGfx/ImageFormats/JPEGXLLoader.cpp
index 52c514380d..a6864b58a2 100644
--- a/Userland/Libraries/LibGfx/ImageFormats/JPEGXLLoader.cpp
+++ b/Userland/Libraries/LibGfx/ImageFormats/JPEGXLLoader.cpp
@@ -398,6 +398,18 @@ struct ImageMetadata {
     Array<double, 15> up2_weight = s_d_up2;
     Array<double, 55> up4_weight = s_d_up4;
     Array<double, 210> up8_weight = s_d_up8;
+
+    u16 number_of_color_channels() const
+    {
+        if (!xyb_encoded && colour_encoding.colour_space == ColourEncoding::ColourSpace::kGrey)
+            return 1;
+        return 3;
+    }
+
+    u16 number_of_channels() const
+    {
+        return number_of_color_channels() + num_extra_channels;
+    }
 };
 
 static ErrorOr<ImageMetadata> read_metadata_header(LittleEndianInputBitStream& stream)
@@ -1169,14 +1181,18 @@ private:
 
 class Image {
 public:
-    static ErrorOr<Image> create(IntSize size)
+    static ErrorOr<Image> create(IntSize size, ImageMetadata const& metadata)
     {
         Image image {};
 
-        // FIXME: Don't assume three channels and a fixed size
-        TRY(image.m_channels.try_append(TRY(Channel::create(size.width(), size.height()))));
-        TRY(image.m_channels.try_append(TRY(Channel::create(size.width(), size.height()))));
-        TRY(image.m_channels.try_append(TRY(Channel::create(size.width(), size.height()))));
+        for (u16 i = 0; i < metadata.number_of_channels(); ++i) {
+            if (i < metadata.number_of_color_channels()) {
+                TRY(image.m_channels.try_append(TRY(Channel::create(size.width(), size.height()))));
+            } else {
+                auto const dim_shift = metadata.ec_info[i - metadata.number_of_color_channels()].dim_shift;
+                TRY(image.m_channels.try_append(TRY(Channel::create(size.width() >> dim_shift, size.height() >> dim_shift))));
+            }
+        }
 
         return image;
     }
@@ -1629,7 +1645,7 @@ static ErrorOr<Frame> read_frame(LittleEndianInputBitStream& stream,
 
     frame.toc = TRY(read_toc(stream, frame.frame_header, frame.num_groups, frame.num_lf_groups));
 
-    image = TRY(Image::create({ frame.width, frame.height }));
+    image = TRY(Image::create({ frame.width, frame.height }, metadata));
 
     frame.lf_global = TRY(read_lf_global(stream, image, frame.frame_header, metadata, entropy_decoder));