Fix incorrect evaluation of resolution media queries

Source/core/css/MediaQueryEvaluator.cpp

 /*
  * CSS Media Query Evaluator
  *
  * Copyright (C) 2006 Kimmo Kinnunen <kimmo.t.kinnunen@nokia.com>.
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 177 matching lines @@
 static bool compareAspectRatioValue(CSSValue* value, int width, int height, MediaFeaturePrefix op)
 {
     if (value->isAspectRatioValue()) {
         CSSAspectRatioValue* aspectRatio = static_cast<CSSAspectRatioValue*>(value);
         return compareValue(width * static_cast<int>(aspectRatio->denominatorValue()), height * static_cast<int>(aspectRatio->numeratorValue()), op);
     }
 
     return false;
 }
 
-#if ENABLE(RESOLUTION_MEDIA_QUERY)
-static bool compareResolution(float min, float max, float value, MediaFeaturePrefix op)
-{
-    switch (op) {
-    case NoPrefix:
-        // A 'resolution' (without a "min-" or "max-" prefix) query
-        // never matches a device with non-square pixels.
-        return value == min && value == max;
-    case MinPrefix:
-        return min >= value;
-    case MaxPrefix:
-        return max <= value;
-    }
-    return false;
-}
-#endif
-
 static bool numberValue(CSSValue* value, float& result)
 {
     if (value->isPrimitiveValue()
         && static_cast<CSSPrimitiveValue*>(value)->isNumber()) {
         result = static_cast<CSSPrimitiveValue*>(value)->getFloatValue(CSSPrimitiveValue::CSS_NUMBER);
         return true;
     }
     return false;
 }
 
@@ skipping 53 matching lines @@
     if (value) {
         FloatRect sg = screenRect(frame->page()->mainFrame()->view());
         return compareAspectRatioValue(value, static_cast<int>(sg.width()), static_cast<int>(sg.height()), op);
     }
 
     // ({,min-,max-}device-aspect-ratio)
     // assume if we have a device, its aspect ratio is non-zero
     return true;
 }
 
-static bool device_pixel_ratioMediaFeatureEval(CSSValue *value, RenderStyle*, Frame* frame, MediaFeaturePrefix op)
+static bool evalResolution(CSSValue* value, Frame* frame, MediaFeaturePrefix op)
 {
     // FIXME: Possible handle other media types than 'screen' and 'print'.
     float deviceScaleFactor = 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".
     String mediaType = frame->view()->mediaType();
     if (equalIgnoringCase(mediaType, "screen"))
         deviceScaleFactor = frame->page()->deviceScaleFactor();
     else if (equalIgnoringCase(mediaType, "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.
         deviceScaleFactor = 3.125; // 300dpi / 96dpi;
     }
 
     if (!value)
         return !!deviceScaleFactor;
 
-    return value->isPrimitiveValue() && compareValue(deviceScaleFactor, static_cast<CSSPrimitiveValue*>(value)->getFloatValue(), op);
+    if (!value->isPrimitiveValue())
+        return false;
+
+    CSSPrimitiveValue* resolution = static_cast<CSSPrimitiveValue*>(value);
+
+    if (resolution->isNumber())
+        compareValue(deviceScaleFactor, resolution->getFloatValue(), op);
+
+    if (resolution->isResolution()) {
+        // To match DPCM and DPI integer values 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 * deviceScaleFactor) / 100,
+            floorf(0.5 + 100 * resolution->getFloatValue(CSSPrimitiveValue::CSS_DPPX)) / 100, op);

[johnme, 2013/04/23 18:16:23]

I don't understand this line. A resolution for which isResolution is true can be
of type DPCM or DPI in addition to DPPX. So how does
resolution->getFloatValue(CSSPrimitiveValue::CSS_DPPX) work? getFloatValue
doesn't seem to do any unit conversions, unless I'm missing something?

+    }
+
+    return false;
+}
+
+static bool device_pixel_ratioMediaFeatureEval(CSSValue *value, RenderStyle*, Frame* frame, MediaFeaturePrefix op)
+{
+    return (!value || static_cast<CSSPrimitiveValue*>(value)->isNumber()) && evalResolution(value, frame, op);
 }
 
 static bool resolutionMediaFeatureEval(CSSValue* value, RenderStyle*, Frame* frame, MediaFeaturePrefix op)
 {
 #if ENABLE(RESOLUTION_MEDIA_QUERY)
-    // The DPI below is dots per CSS inch and thus not device inch. The
-    // functions should respect this.
-    //
-    // For square pixels, it is simply the device scale factor (dppx) times 96,
-    // per definition.
-    //
-    // The device scale factor is a predefined value which is calculated per
-    // device given the preferred distance in arms length (considered one arms
-    // length for desktop computers and usually 0.6 arms length for phones).
-    //
-    // The value can be calculated as follows (rounded to quarters):
-    //     round((deviceDotsPerInch * distanceInArmsLength / 96) * 4) / 4.
-    // Example (mid-range resolution phone):
-    //     round((244 * 0.6 / 96) * 4) / 4 = 1.5
-    // Example (high-range resolution laptop):
-    //     round((220 * 1.0 / 96) * 4) / 4 = 2.0
-
-    float horiDPI;
-    float vertDPI;
-
-    // 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".
-    String mediaType = frame->view()->mediaType();
-    if (equalIgnoringCase(mediaType, "screen")) {
-        Screen* screen = frame->document()->domWindow()->screen();
-        horiDPI = screen->horizontalDPI();
-        vertDPI = screen->verticalDPI();
-    } else if (equalIgnoringCase(mediaType, "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.
-        horiDPI = vertDPI = 300;
-    } else {
-        // FIXME: Possible handle other media types than 'screen' and 'print'.
-        // For now, do not match.
-        return false;
-    }
-
-    float leastDenseDPI = std::min(horiDPI, vertDPI);
-    float mostDenseDPI = std::max(horiDPI, vertDPI);
-
-    // According to spec, (resolution) will evaluate to true if (resolution:x)
-    // will evaluate to true for a value x other than zero or zero followed by
-    // a valid unit identifier (i.e., other than 0, 0dpi, 0dpcm, or 0dppx.),
-    // which is always the case. But the spec special cases 'resolution' to
-    // never matches a device with non-square pixels.
-    if (!value) {
-        ASSERT(op == NoPrefix);
-        return leastDenseDPI == mostDenseDPI;
-    }
-
-    if (!value->isPrimitiveValue())
-        return false;
-
-    // http://dev.w3.org/csswg/css3-values/#resolution defines resolution as a
-    // dimension, which contains a number (decimal point allowed), not just an
-    // integer. Also, http://dev.w3.org/csswg/css3-values/#numeric-types says
-    // "CSS theoretically supports infinite precision and infinite ranges for
-    // all value types;
-    CSSPrimitiveValue* rawValue = static_cast<CSSPrimitiveValue*>(value);
-
-    if (rawValue->isDotsPerPixel()) {
-        // 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". We compare with 3 decimal
-        // points, which aligns with current device-pixel-ratio's in use.
-        float leastDenseDensity = floorf(leastDenseDPI * 1000 / 96) / 1000;
-        float mostDenseDensity = floorf(leastDenseDPI * 1000 / 96) / 1000;
-        float testedDensity = rawValue->getFloatValue(CSSPrimitiveValue::CSS_DPPX);
-        return compareResolution(leastDenseDensity, mostDenseDensity, testedDensity, op);
-    }
-
-    if (rawValue->isDotsPerInch()) {
-        unsigned testedDensity = rawValue->getFloatValue(CSSPrimitiveValue::CSS_DPI);
-        return compareResolution(leastDenseDPI, mostDenseDPI, testedDensity, op);
-    }
-
-    // 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".
-    float leastDenseDPCM = roundf(leastDenseDPI / 2.54); // (2.54 cm/in)
-    float mostDenseDPCM = roundf(mostDenseDPI / 2.54);
-
-    if (rawValue->isDotsPerCentimeter()) {
-        float testedDensity = rawValue->getFloatValue(CSSPrimitiveValue::CSS_DPCM);
-        return compareResolution(leastDenseDPCM, mostDenseDPCM, testedDensity, op);
-    }
+    return (!value || static_cast<CSSPrimitiveValue*>(value)->isResolution()) && evalResolution(value, frame, op);
 #else
     UNUSED_PARAM(value);
     UNUSED_PARAM(frame);
     UNUSED_PARAM(op);
-#endif
 
     return false;
+#endif
 }
 
 static bool gridMediaFeatureEval(CSSValue* value, RenderStyle*, Frame*, MediaFeaturePrefix op)
 {
     // if output device is bitmap, grid: 0 == true
     // assume we have bitmap device
     float number;
     if (value && numberValue(value, number))
         return compareValue(static_cast<int>(number), 0, op);
     return false;
@@ skipping 347 matching lines @@
     // and let trampoline functions override the prefix if prefix is
     // used
     EvalFunc func = gFunctionMap->get(expr->mediaFeature().impl());
     if (func)
         return func(expr->value(), m_style.get(), m_frame, NoPrefix);
 
     return false;
 }
 
 } // namespace