LibGfx: Correctly decode webp lossless with small palette and odd width

WebP lossless files that use a color indexing transform with <= 16
colors use pixel bundling to pack 2, 4, or 8 pixels into a single pixel.

If the image's width doesn't happen to be an exact multiple of the
bundling factor, we need to:

1. Use ceil_div() instead of just dividing the width by the bundling
   factor

2. Remember the original width and use it instead of computing
   reduced width times bundling factor

This does these changes, and adds a simple test for it -- it at least
checks that the decoded images have the right size.

(I created these images myself in Photoshop, and used the same
technique as for Tests/LibGfx/test-inputs/catdog-alert-*.webp
to create images with a certain number of colors.)

4 files changed, 21 insertions, 0 deletions

diff --git a/Tests/LibGfx/TestImageDecoder.cpp b/Tests/LibGfx/TestImageDecoder.cpp
index c8e2ced9a3..4a843d37e0 100644
--- a/Tests/LibGfx/TestImageDecoder.cpp
+++ b/Tests/LibGfx/TestImageDecoder.cpp
@@ -420,6 +420,27 @@ TEST_CASE(test_webp_simple_lossless_color_index_transform_pixel_bundling)
     }
 }
 
+TEST_CASE(test_webp_simple_lossless_color_index_transform_pixel_bundling_odd_width)
+{
+    StringView file_names[] = {
+        "width11-height11-colors2.webp"sv,
+        "width11-height11-colors3.webp"sv,
+        "width11-height11-colors15.webp"sv,
+    };
+
+    for (auto file_name : file_names) {
+        auto file = MUST(Core::MappedFile::map(MUST(String::formatted("{}{}", TEST_INPUT(""), file_name))));
+        auto plugin_decoder = MUST(Gfx::WebPImageDecoderPlugin::create(file->bytes()));
+        EXPECT(plugin_decoder->initialize());
+
+        EXPECT_EQ(plugin_decoder->frame_count(), 1u);
+        EXPECT_EQ(plugin_decoder->size(), Gfx::IntSize(11, 11));
+
+        auto frame = MUST(plugin_decoder->frame(0));
+        EXPECT_EQ(frame.image->size(), Gfx::IntSize(11, 11));
+    }
+}
+
 TEST_CASE(test_webp_extended_lossless_animated)
 {
     auto file = MUST(Core::MappedFile::map(TEST_INPUT("extended-lossless-animated.webp"sv)));
diff --git a/Tests/LibGfx/test-inputs/width11-height11-colors15.webp b/Tests/LibGfx/test-inputs/width11-height11-colors15.webp
new file mode 100644
index 0000000000..cfb395d11a
--- /dev/null
+++ b/Tests/LibGfx/test-inputs/width11-height11-colors15.webp
diff --git a/Tests/LibGfx/test-inputs/width11-height11-colors2.webp b/Tests/LibGfx/test-inputs/width11-height11-colors2.webp
new file mode 100644
index 0000000000..8e213bda95
--- /dev/null
+++ b/Tests/LibGfx/test-inputs/width11-height11-colors2.webp
diff --git a/Tests/LibGfx/test-inputs/width11-height11-colors3.webp b/Tests/LibGfx/test-inputs/width11-height11-colors3.webp
new file mode 100644
index 0000000000..c11285c401
--- /dev/null
+++ b/Tests/LibGfx/test-inputs/width11-height11-colors3.webp