Display Units

The core method getDisplayConfiguration will return numeric values representing various properties of the connected displays.

These values differ in their units between Windows and Mac. Windows will return pixel values. OS X uses the term "points" for logical display units. Readers with knowledge of print units be warned: "points" has a different meaning here.

See developer.apple.com for a detailed explanation on the topic of points and logical resolution.

Examples

On a 27" 4k display we receive the following output (edited for brevity).

Windows with scale set to 2.

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{
    "globalBounds": {
        "bottom": 2160,
        "left": 0,
        "right": 3840,
        "top": 0
    },
    "physicalResolution": {
        "horizontal": 163,
        "vertical": 163
    },
    "scaleFactor": 2,
}
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{
    "globalBounds": {
        "bottom": 2160,
        "left": 0,
        "right": 3840,
        "top": 0
    },
    "physicalResolution": {
        "horizontal": 163,
        "vertical": 163
    },
    "scaleFactor": 2,
}

Mac with Display Options > Use as: 1920x1080.

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{
    "globalBounds": {
        "bottom": 1080,
        "left": 0,
        "right": 1920,
        "top": 0
    },
    "physicalResolution": {
        "horizontal": 163.00000244801444,
        "vertical": 161.00000241797744
    },
    "scaleFactor": 2,
}
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{
    "globalBounds": {
        "bottom": 1080,
        "left": 0,
        "right": 1920,
        "top": 0
    },
    "physicalResolution": {
        "horizontal": 163.00000244801444,
        "vertical": 161.00000241797744
    },
    "scaleFactor": 2,
}

Note that on Windows we see the full pixel count and the pixels-per-inch (ppi) is 163 as expected. On Mac, we see the same values in globalBounds as was set in the OS Display Options.

Interestingly, when we change the option "Use as" to 3200x1800, we see:

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{
    "globalBounds": {
        "bottom": 1800,
        "left": 0,
        "right": 3200,
        "top": 0
    },
    "physicalResolution": {
        "horizontal": 271.0000040700117,
        "vertical": 269.0000040399747
    }
}
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{
    "globalBounds": {
        "bottom": 1800,
        "left": 0,
        "right": 3200,
        "top": 0
    },
    "physicalResolution": {
        "horizontal": 271.0000040700117,
        "vertical": 269.0000040399747
    }
}

We also see above that the "horizontal" value has changed to 271.

Dividing the horizontal point count by the "physicalResolution" value: 3200 / 271 ~= 11.8. This result matches that of the first block above 1920 / 163 ~= 11.8.