ladybird/Libraries/LibWeb/HTML/Canvas/CanvasTextDrawingStyles.cpp

/*
 * Copyright (c) 2023, Bastiaan van der Plaat <bastiaan.v.d.plaat@gmail.com>
 * Copyright (c) 2023, Callum Law <callumlaw1709@outlook.com>
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include "CanvasTextDrawingStyles.h"
#include <LibWeb/CSS/ComputedProperties.h>
#include <LibWeb/CSS/StyleComputer.h>
#include <LibWeb/CSS/StyleValues/FontStyleStyleValue.h>
#include <LibWeb/CSS/StyleValues/LengthStyleValue.h>
#include <LibWeb/CSS/StyleValues/NumberStyleValue.h>
#include <LibWeb/CSS/StyleValues/PercentageStyleValue.h>
#include <LibWeb/CSS/StyleValues/ShorthandStyleValue.h>
#include <LibWeb/HTML/Canvas/CanvasState.h>
#include <LibWeb/HTML/CanvasRenderingContext2D.h>
#include <LibWeb/HTML/OffscreenCanvas.h>
#include <LibWeb/HTML/OffscreenCanvasRenderingContext2D.h>
#include <LibWeb/HTML/Window.h>
#include <LibWeb/HTML/WorkerGlobalScope.h>

namespace Web::HTML {

template<typename IncludingClass, typename CanvasType>
ByteString CanvasTextDrawingStyles<IncludingClass, CanvasType>::font() const
{
    // When font style value is empty return default string
    if (!my_drawing_state().font_style_value) {
        return "10px sans-serif";
    }

    // On getting, the font attribute must return the serialized form of the current font of the context (with no 'line-height' component).
    auto const& font_style_value = my_drawing_state().font_style_value->as_shorthand();
    auto font_style = font_style_value.longhand(CSS::PropertyID::FontStyle);
    auto font_weight = font_style_value.longhand(CSS::PropertyID::FontWeight);
    auto font_size = font_style_value.longhand(CSS::PropertyID::FontSize);
    auto font_family = font_style_value.longhand(CSS::PropertyID::FontFamily);
    return ByteString::formatted("{} {} {} {}",
        font_style->to_string(CSS::SerializationMode::Normal),
        font_weight->to_string(CSS::SerializationMode::Normal),
        font_size->to_string(CSS::SerializationMode::Normal),
        font_family->to_string(CSS::SerializationMode::Normal));
}

// https://html.spec.whatwg.org/multipage/canvas.html#font-style-source-object
template<typename IncludingClass, typename CanvasType>
Variant<DOM::Document*, HTML::WorkerGlobalScope*> CanvasTextDrawingStyles<IncludingClass, CanvasType>::get_font_source_for_font_style_source_object(CanvasType& font_style_source_object)
{
    // Font resolution for the font style source object requires a font source. This is determined for a given object implementing CanvasTextDrawingStyles by the following steps: [CSSFONTLOAD]

    if constexpr (SameAs<CanvasType, HTML::HTMLCanvasElement>) {
        // 1. If object's font style source object is a canvas element, return the element's node document.
        return &font_style_source_object.document();
    } else {
        // 2. Otherwise, object's font style source object is an OffscreenCanvas object:

        // 1. Let global be object's relevant global object.
        auto& global_object = HTML::relevant_global_object(font_style_source_object);

        // 2. If global is a Window object, then return global's associated Document.
        if (is<HTML::Window>(global_object)) {
            auto& window = as<HTML::Window>(global_object);
            return &(window.associated_document());
        }

        // 3. Assert: global implements WorkerGlobalScope.
        VERIFY(is<HTML::WorkerGlobalScope>(global_object));

        // 4. Return global.
        return &(as<HTML::WorkerGlobalScope>(global_object));
    };
}
template<typename IncludingClass, typename CanvasType>
void CanvasTextDrawingStyles<IncludingClass, CanvasType>::set_font(StringView font)
{
    // The font IDL attribute, on setting, must be parsed as a CSS <'font'> value (but without supporting property-independent style sheet syntax like 'inherit'),
    // and the resulting font must be assigned to the context, with the 'line-height' component forced to 'normal', with the 'font-size' component converted to CSS pixels,
    // and with system fonts being computed to explicit values.
    // FIXME: with the 'line-height' component forced to 'normal'
    // FIXME: with the 'font-size' component converted to CSS pixels
    // FIXME: Disallow tree counting functions if this is an offscreen canvas
    auto font_style_value_result = parse_css_value(CSS::Parser::ParsingParams {}, font, CSS::PropertyID::Font);

    // If the new value is syntactically incorrect (including using property-independent style sheet syntax like 'inherit' or 'initial'), then it must be ignored, without assigning a new font value.
    // NOTE: ShorthandStyleValue should be the only valid option here. We implicitly VERIFY this below.
    if (!font_style_value_result || !font_style_value_result->is_shorthand()) {
        return;
    }
    my_drawing_state().font_style_value = font_style_value_result.release_nonnull();

    // Load font with font style value properties
    auto const& font_style_value = my_drawing_state().font_style_value->as_shorthand();
    auto& canvas_element = reinterpret_cast<IncludingClass&>(*this).canvas_element();

    auto& font_style = *font_style_value.longhand(CSS::PropertyID::FontStyle);
    auto& font_weight = *font_style_value.longhand(CSS::PropertyID::FontWeight);
    auto& font_width = *font_style_value.longhand(CSS::PropertyID::FontWidth);
    auto& font_size = *font_style_value.longhand(CSS::PropertyID::FontSize);
    auto& font_family = *font_style_value.longhand(CSS::PropertyID::FontFamily);

    // https://drafts.csswg.org/css-font-loading/#font-source
    auto font_source = get_font_source_for_font_style_source_object(canvas_element);

    auto font_list = font_source.visit(
        [&](DOM::Document* document) -> RefPtr<Gfx::FontCascadeList const> {
            auto computed_math_depth = CSS::InitialValues::math_depth();
            auto inherited_math_depth = CSS::InitialValues::math_depth();

            // NOTE: The initial value here is non-standard as the default font is "10px sans-serif"
            auto inherited_font_size = CSSPixels { 10 };
            auto inherited_font_weight = CSS::InitialValues::font_weight();
            // FIXME: Investigate whether this is the correct resolution context (i.e. whether we should instead use
            //        a font-size of 10px) for OffscreenCanvas
            auto length_resolution_context = CSS::Length::ResolutionContext::for_window(*document->window());
            Optional<DOM::AbstractElement> abstract_element;

            if constexpr (SameAs<CanvasType, HTML::HTMLCanvasElement>) {
                // NOTE: The canvas itself is considered the inheritance parent
                if (canvas_element.computed_properties()) {
                    // NOTE: Since we can't set a math depth directly here we always use the inherited value for the computed value
                    computed_math_depth = canvas_element.computed_properties()->math_depth();
                    inherited_math_depth = canvas_element.computed_properties()->math_depth();
                    inherited_font_size = canvas_element.computed_properties()->font_size();
                    inherited_font_weight = canvas_element.computed_properties()->font_weight();

                    abstract_element = DOM::AbstractElement { canvas_element };

                    length_resolution_context = CSS::Length::ResolutionContext::for_element(abstract_element.value());
                }
            }

            CSS::ComputationContext computation_context {
                .length_resolution_context = length_resolution_context,
                .abstract_element = abstract_element
            };

            // FIXME: Should font be recomputed on canvas element style change?
            auto const& computed_font_size = CSS::StyleComputer::compute_font_size(font_size, computed_math_depth, inherited_font_size, inherited_math_depth, computation_context);
            auto const& computed_font_weight = CSS::StyleComputer::compute_font_weight(font_weight, inherited_font_weight, computation_context);
            auto const& computed_font_width = CSS::StyleComputer::compute_font_width(font_width, computation_context);
            auto const& computed_font_style = CSS::StyleComputer::compute_font_style(font_style, computation_context);

            return document->style_computer().compute_font_for_style_values(
                font_family,
                computed_font_size->as_length().length().absolute_length_to_px(),
                computed_font_style->as_font_style().to_font_slope(),
                computed_font_weight->as_number().number(),
                computed_font_width->as_percentage().percentage());
        },
        [](HTML::WorkerGlobalScope*) -> RefPtr<Gfx::FontCascadeList const> {
            // FIXME: implement computing the font for HTML::WorkerGlobalScope
            return {};
        });

    if (!font_list)
        return;

    my_drawing_state().current_font_cascade_list = font_list;
}

template class CanvasTextDrawingStyles<CanvasRenderingContext2D, HTMLCanvasElement>;
template class CanvasTextDrawingStyles<OffscreenCanvasRenderingContext2D, HTML::OffscreenCanvas>;

}