SizesAttributeParser.cpp   [plain text]

// Copyright 2014 The Chromium Authors. All rights reserved.
// Copyright (C) 2016 Apple Inc. All rights reserved.
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#include "config.h"
#include "SizesAttributeParser.h"

#include "CSSPrimitiveValue.h"
#include "CSSToLengthConversionData.h"
#include "CSSTokenizer.h"
#include "FontCascade.h"
#include "MediaList.h"
#include "MediaQueryEvaluator.h"
#include "MediaQueryParser.h"
#include "MediaQueryParserContext.h"
#include "RenderView.h"
#include "SizesCalcParser.h"
#include "StyleScope.h"

namespace WebCore {

float SizesAttributeParser::computeLength(double value, CSSPrimitiveValue::UnitType type, const Document& document)
{
    auto* renderer = document.renderView();
    if (!renderer)
        return 0;
    auto& style = renderer->style();

    CSSToLengthConversionData conversionData(&style, &style, renderer);
    
    // Because we evaluate "sizes" at parse time (before style has been resolved), the font metrics used for these specific units
    // are not available. The font selector's internal consistency isn't guaranteed just yet, so we can just temporarily clear
    // the pointer to it for the duration of the unit evaluation. This is acceptible because the style always comes from the
    // RenderView, which has its font information hardcoded in resolveForDocument() to be -webkit-standard, whose operations
    // don't require a font selector.
    if (type == CSSPrimitiveValue::CSS_EXS || type == CSSPrimitiveValue::CSS_CHS) {
        RefPtr<FontSelector> fontSelector = style.fontCascade().fontSelector();
        style.fontCascade().update(nullptr);
        float result = CSSPrimitiveValue::computeNonCalcLengthDouble(conversionData, type, value);
        style.fontCascade().update(fontSelector.get());
        return result;
    }
    
    return clampTo<float>(CSSPrimitiveValue::computeNonCalcLengthDouble(conversionData, type, value));
}
    
SizesAttributeParser::SizesAttributeParser(const String& attribute, const Document& document)
    : m_document(document)
    , m_length(0)
    , m_lengthWasSet(false)
{
    m_isValid = parse(CSSTokenizer(attribute).tokenRange());
}

float SizesAttributeParser::length()
{
    if (m_isValid)
        return effectiveSize();
    return effectiveSizeDefaultValue();
}

bool SizesAttributeParser::calculateLengthInPixels(CSSParserTokenRange range, float& result)
{
    const CSSParserToken& startToken = range.peek();
    CSSParserTokenType type = startToken.type();
    if (type == DimensionToken) {
        if (!CSSPrimitiveValue::isLength(startToken.unitType()))
            return false;
        result = computeLength(startToken.numericValue(), startToken.unitType(), m_document);
        if (result >= 0)
            return true;
    } else if (type == FunctionToken) {
        SizesCalcParser calcParser(range, m_document);
        if (!calcParser.isValid())
            return false;
        result = calcParser.result();
        return true;
    } else if (type == NumberToken && !startToken.numericValue()) {
        result = 0;
        return true;
    }

    return false;
}

bool SizesAttributeParser::mediaConditionMatches(const MediaQuerySet& mediaCondition)
{
    // A Media Condition cannot have a media type other than screen.
    auto* renderer = m_document.renderView();
    if (!renderer)
        return false;
    auto& style = renderer->style();
    return MediaQueryEvaluator { "screen", m_document, &style }.evaluate(mediaCondition, const_cast<Style::Scope&>(m_document.styleScope()).resolverIfExists());
}

bool SizesAttributeParser::parse(CSSParserTokenRange range)
{
    // Split on a comma token and parse the result tokens as (media-condition, length) pairs
    while (!range.atEnd()) {
        const CSSParserToken* mediaConditionStart = &range.peek();
        // The length is the last component value before the comma which isn't whitespace or a comment
        const CSSParserToken* lengthTokenStart = &range.peek();
        const CSSParserToken* lengthTokenEnd = &range.peek();
        while (!range.atEnd() && range.peek().type() != CommaToken) {
            lengthTokenStart = &range.peek();
            range.consumeComponentValue();
            lengthTokenEnd = &range.peek();
            range.consumeWhitespace();
        }
        range.consume();

        float length;
        if (!calculateLengthInPixels(range.makeSubRange(lengthTokenStart, lengthTokenEnd), length))
            continue;
        RefPtr<MediaQuerySet> mediaCondition = MediaQueryParser::parseMediaCondition(range.makeSubRange(mediaConditionStart, lengthTokenStart), MediaQueryParserContext(m_document));
        if (!mediaCondition || !mediaConditionMatches(*mediaCondition))
            continue;
        m_length = length;
        m_lengthWasSet = true;
        return true;
    }
    return false;
}

float SizesAttributeParser::effectiveSize()
{
    if (m_lengthWasSet)
        return m_length;
    return effectiveSizeDefaultValue();
}

unsigned SizesAttributeParser::effectiveSizeDefaultValue()
{
    auto* renderer = m_document.renderView();
    if (!renderer)
        return 0;
    auto& style = renderer->style();
    return clampTo<float>(CSSPrimitiveValue::computeNonCalcLengthDouble({ &style, &style, renderer }, CSSPrimitiveValue::CSS_VW, 100.0));
}

} // namespace WebCore