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LibWeb: Implement HTMLCanvasElement.toDataURL() closer to spec

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- Requesting an unsupported image type will now fallback to PNG
  (which is now always the case),
- Errors should return 'data:,' instead of empty string,
- Added spec comments
This commit is contained in:
Karol Kosek 2023-08-03 10:12:11 +02:00 • committed by Andreas Kling
parent 55af4addc8
commit 3239f0fb7b
1 changed files with 33 additions and 12 deletions
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45
Userland/Libraries/LibWeb/HTML/HTMLCanvasElement.cpp
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@ -179,23 +179,44 @@ bool HTMLCanvasElement::create_bitmap(size_t minimum_width, size_t minimum_heigh
return m_bitmap;
}
DeprecatedString HTMLCanvasElement::to_data_url(DeprecatedString const& type, [[maybe_unused]] Optional<double> quality) const
struct SerializeBitmapResult {
ByteBuffer buffer;
StringView mime_type;
};
// https://html.spec.whatwg.org/multipage/canvas.html#a-serialisation-of-the-bitmap-as-a-file
static ErrorOr<SerializeBitmapResult> serialize_bitmap(Gfx::Bitmap const& bitmap, [[maybe_unused]] StringView type, [[maybe_unused]] Optional<double> quality)
{
// User agents must support PNG ("image/png"). User agents may support other types.
// If the user agent does not support the requested type, then it must create the file using the PNG format. [PNG]
return SerializeBitmapResult { TRY(Gfx::PNGWriter::encode(bitmap)), "image/png"sv };
}
// https://html.spec.whatwg.org/multipage/canvas.html#dom-canvas-todataurl
DeprecatedString HTMLCanvasElement::to_data_url(DeprecatedString const& type, Optional<double> quality) const
{
// FIXME: 1. If this canvas element's bitmap's origin-clean flag is set to false, then throw a "SecurityError" DOMException.
// 2. If this canvas element's bitmap has no pixels (i.e. either its horizontal dimension or its vertical dimension is zero)
// then return the string "data:,". (This is the shortest data: URL; it represents the empty string in a text/plain resource.)
if (!m_bitmap)
return {};
if (type != "image/png")
return {};
auto encoded_bitmap_or_error = Gfx::PNGWriter::encode(*m_bitmap);
if (encoded_bitmap_or_error.is_error()) {
dbgln("Gfx::PNGWriter failed to encode the HTMLCanvasElement: {}", encoded_bitmap_or_error.error());
return {};
return "data:,";
// 3. Let file be a serialization of this canvas element's bitmap as a file, passing type and quality if given.
auto file = serialize_bitmap(*m_bitmap, type, move(quality));
// 4. If file is null then return "data:,".
if (file.is_error()) {
dbgln("HTMLCanvasElement: Failed to encode canvas bitmap to {}: {}", type, file.error());
return "data:,";
}
auto base64_encoded_or_error = encode_base64(encoded_bitmap_or_error.value());
// 5. Return a data: URL representing file. [RFC2397]
auto base64_encoded_or_error = encode_base64(file.value().buffer);
if (base64_encoded_or_error.is_error()) {
// FIXME: propagate error
return {};
return "data:,";
}
return AK::URL::create_with_data(type, base64_encoded_or_error.release_value(), true).to_deprecated_string();
return AK::URL::create_with_data(file.value().mime_type, base64_encoded_or_error.release_value(), true).to_deprecated_string();
}
void HTMLCanvasElement::present()