static bool evalResolution(const MediaQueryExpValue& value, MediaFeaturePrefix op, const MediaValues& mediaValues)
{
// According to MQ4, only 'screen', 'print' and 'speech' may match.
// FIXME: What should speech match? https://www.w3.org/Style/CSS/Tracker/issues/348
float actualResolution = 0;
// This checks the actual media type applied to the document, and we know
// this method only got called if this media type matches the one defined
// in the query. Thus, if if the document's media type is "print", the
// media type of the query will either be "print" or "all".
if (equalIgnoringCase(mediaValues.mediaType(), MediaTypeNames::screen)) {
actualResolution = clampTo<float>(mediaValues.devicePixelRatio());
} else if (equalIgnoringCase(mediaValues.mediaType(), MediaTypeNames::print)) {
// The resolution of images while printing should not depend on the DPI
// of the screen. Until we support proper ways of querying this info
// we use 300px which is considered minimum for current printers.
actualResolution = 300 / cssPixelsPerInch;
}
if (!value.isValid())
return !!actualResolution;
if (!value.isValue)
return false;
if (value.unit == CSSPrimitiveValue::CSS_NUMBER)
return compareValue(actualResolution, clampTo<float>(value.value), op);
if (!CSSPrimitiveValue::isResolution(value.unit))
return false;
double canonicalFactor = CSSPrimitiveValue::conversionToCanonicalUnitsScaleFactor(value.unit);
double dppxFactor = CSSPrimitiveValue::conversionToCanonicalUnitsScaleFactor(CSSPrimitiveValue::CSS_DPPX);
float valueInDppx = clampTo<float>(value.value * (canonicalFactor / dppxFactor));
if (CSSPrimitiveValue::isDotsPerCentimeter(value.unit)) {
// To match DPCM to DPPX values, we limit to 2 decimal points.
// The http://dev.w3.org/csswg/css3-values/#absolute-lengths recommends
// "that the pixel unit refer to the whole number of device pixels that best
// approximates the reference pixel". With that in mind, allowing 2 decimal
// point precision seems appropriate.
return compareValue(
floorf(0.5 + 100 * actualResolution) / 100,
floorf(0.5 + 100 * valueInDppx) / 100, op);
}
return compareValue(actualResolution, valueInDppx, op);
}
static bool scanMediaFeatureEval(const MediaQueryExpValue& value, MediaFeaturePrefix, const MediaValues& mediaValues)
{
// Scan only applies to 'tv' media.
if (!equalIgnoringCase(mediaValues.mediaType(), MediaTypeNames::tv))
return false;
if (!value.isValid())
return true;
if (!value.isID)
return false;
// If a platform interface supplies progressive/interlace info for TVs in the
// future, it needs to be handled here. For now, assume a modern TV with
// progressive display.
return (value.id == CSSValueProgressive);
}