LibGfx: Fix incorrect colors in ICO-embedded BMPs

Author: https://github.com/aplefull
Commit: e0ceb66580
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4447
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibGfx/ImageFormats/BMPLoader.cpp

@@ -1379,12 +1379,18 @@ static ErrorOr<void> decode_bmp_pixel_data(BMPLoadingContext& context)
                     return Error::from_string_literal("Cannot read 24 bits");
 
                 u32 pixel = streamer.read_u24();
-                u8 b = (pixel & 0xFF0000) >> 16;
-                u8 g = (pixel & 0x00FF00) >> 8;
-                u8 r = (pixel & 0x0000FF);
 
-                u32 rgbx_pixel = (r << 16) | (g << 8) | b;
-                context.bitmap->scanline(row)[column++] = rgbx_pixel;
+                if (context.is_included_in_ico) {
+                    // 24-bit ICO files already use BGRA8888 format
+                    context.bitmap->scanline(row)[column++] = pixel;
+                } else {
+                    u8 b = (pixel & 0x0000FF);
+                    u8 g = (pixel & 0x00FF00) >> 8;
+                    u8 r = (pixel & 0xFF0000) >> 16;
+
+                    context.bitmap->scanline(row)[column++] = (b << 16) | (g << 8) | r;
+                }
+
                 break;
             }
             case 32:

Tests/LibGfx/TestImageDecoder.cpp

@@ -192,6 +192,17 @@ TEST_CASE(test_bmp_embedded_in_ico)
     EXPECT_EQ(frame.image->get_pixel(7, 4), Gfx::Color(161, 0, 0));
 }
 
+TEST_CASE(test_24bit_bmp_embedded_in_ico)
+{
+    auto file = TRY_OR_FAIL(Core::MappedFile::map(TEST_INPUT("ico/yt-favicon.ico"sv)));
+    EXPECT(Gfx::ICOImageDecoderPlugin::sniff(file->bytes()));
+    auto plugin_decoder = TRY_OR_FAIL(Gfx::ICOImageDecoderPlugin::create(file->bytes()));
+
+    auto frame = TRY_OR_FAIL(expect_single_frame_of_size(*plugin_decoder, { 16, 16 }));
+    EXPECT_EQ(frame.image->get_pixel(14, 14), Gfx::Color(234, 0, 0));
+    EXPECT_EQ(frame.image->get_pixel(13, 15), Gfx::Color(255, 10, 15));
+}
+
 TEST_CASE(test_malformed_maskless_ico)
 {
     auto file = TRY_OR_FAIL(Core::MappedFile::map(TEST_INPUT("ico/malformed_maskless.ico"sv)));