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Windows 7: More Follow up to discussion about High DPI

17 Sep 2008   #1

More Follow up to discussion about High DPI


Excellent! What a fun discussion we’ve been having on High DPI. It has been so enriching that Ryan wrote up a summary of even more of the discussion. Thanks so much! --Steven

There have been quite a few comments posted regarding high DPI, along with some lively discussion. Most of what has been said has been good anecdotal examples which are consistent with the data we have collected. For the areas where we didn’t have data, the comments have helped to validate many of our assumptions for this group. It is also clear that there are some areas of this feature which are confusing, and in some cases there is a bit of “myth” around what is ideal, what is possible, and what is there. This follow up post is mostly to summarize what we have heard, and to provide some details around the areas where there has been a bit of confusion.

Here is a list of our top “assumptions” which have been echoed by the comments posted:
  • Most people adjust the screen resolution either to get larger text, or because it was an accident
  • There is a core of people who know about high DPI and who use it
  • Some people prefer more screen real-estate while others people prefer larger UI
  • Discoverability of the DPI configuration is a concern for some
  • App compat is a common issue, even a “deal breaker” in some cases
  • IE Scaling is one of the top issues listed (see IE8 which fixes many of these!)
  • Lots of complexities/subtleties and it is pretty hard to explain this feature to most people
There have also been a number of areas where there has been a bit of confusion:
  • Is it true that if everything were vector-based, these problems would all go away?
  • Shouldn’t this just work without developers having to do anything?
  • How is this different from per-application scaling like IE zooming?
  • Should DPI be for calibration or for scaling?
Most of these topics have been covered to some degree in the comments, but since there has been so much interest, we decided to go into a bit more details around a few of the top issues/concerns.

Vector Graphics vs. Raster Graphics

With PCs, there is always the hope of a “silver bullet” technology which solves all problems making life easy for users, developers, and designers across the board. As an example, some of the comments to the original posting suggested that if we just made the OS fully vector based, these scaling problems would go away. It turns out that there are several issues with using vector graphics which are worth explaining.

The first issue is that oftentimes when an icon gets to be small in size, it is better to use an alternate representation so that the meaning is clearer. Notice the icons below. In this case, the designer has chosen a non-perspective view for the icon when it is rendered at it’s smallest size.

This is because the designer felt that the information expressed by the icon was clearer with a straight-on view at the smallest size. Here is another example illustrating this point:

Of course, this means that the designer must create multiple versions of the source image design, so there is additional complexity. The point here is that there is a tradeoff that must be made and the tradeoff is not always clear.

Even when one vector source is used, it is common to have size-dependent tweaking to make sure that the result is true to what the designer had in mind. Imagine a vector graphic which has a 1-pixel line at 128x128 that gets scaled down by 1/2 to 64x64. The display has no way of rendering a perfect 1/2 pixel line! In many cases the answer is that the renderer will “round” to a nearby pixel line. However, doing this inherently changes the layout of the sub-elements of the image. And there is the question of, “which pixel line to round to?” If the designer does not hand tune the source material, it will be up to the rendering engine to make this decision, and that can result in undesirable effects. One could say that this should therefore define rules about what elements should be use in a vector, but that only further restricts what concepts can be represented.

It turns out that even the TrueType fonts which we use in Windows are hand-tuned with size-dependant information in order to make the result as high quality as possible. Most of the TrueType rendering pipeline is based on algorithmic scaling of a vector source, but there are size-dependent, hand-coded “hints” in TrueType which the designer specifies to direct the system how to handle edge cases, such as lines falling between pixel boundaries. Here is a link describing this in more detail:

It is not even true that vector graphics are necessarily smaller in size (especially for small images). Most designers create graphics using an editor which builds up an image using many layers of drawings and effects. With bitmap based graphics, designers will “flatten” the layers before adding it to a piece of software. Most designers today pay little attention to the size of the layers because the flattening process essentially converts it to a fixed size based on the image resolution. With vector graphics, there is no such flattening technique so designers need to carefully consider the tools that they use and the effects that they add to make sure that their icon is not extremely large. I spent some time with one of our designers who had a vector graphic source for one of our bitmaps in Windows and the file was 622k! Of course that file size is fixed regardless of the resulting resolution, but that huge file flattens into this 23k PNG bitmap.

Of course, a hand-tuned vector based representation of this could be probably made smaller if the size constraints were part of the design time process. But that would be an additional constraint put on the designer, and one which they would need to learn how to do well.

How do we help developers?

For applications that need to carefully control the layout and graphics, or scale the fidelity of the images based on the available resolution, having a way of specifying specific pixel locations for items is important to get the best result. This is as true on the Mac as it is on the PC (see There is often a belief that if we just provided the right tools or the right framework then all these problems would go away. We all know that each set of tools and each framework have their own set of tradeoffs (whether that is Win 32, .net, or HTML). While there is no silver bullet, there are things we can do to make writing DPI aware applications easier for developers. As an example, there are two important upcoming ecosystem events in which we will be talking in detail about High DPI. We will also have materials which we will be making available to developers which will help educate them on how to convert existing applications to be DPI aware. The first event is Microsoft Professional Developer Conference, where we will talk about High DPI as part of the talk “Writing your Application to Shine on Modern Graphics Hardware (link)”. The second is the Windows Hardware Engineering Conference, in which we will be discussing high DPI as part of the “High Fidelity Graphics and Media” track (link).

Help with App Compat Issues

There have been several posts on app compat and high DPI (for example bluvg’s comment). There have also been comments talking about the complexity and understandability of the High DPI configuration. In some cases the app compat issues can be mitigated by enabling or disabling the automatic scaling feature. This can be changed globally by going to the DPI UI, clicking the button labeled “Custom DPI” and changing the checkbox labeled, “Use Windows XP style DPI scaling”. When this checkbox is unchecked, applications which are not declared to be DPI aware are automatically scaled by the window manager. When it is checked, automatic scaling is disabled globally. It is interesting to note that for DPI settings < 144 DPI, this box is checked by default, and for DPI settings >= 144 it is unchecked by default. In some cases, changing the default settings can result in a better experience depending on the applications that you use and your DPI setting. It is also interesting to note that automatic scaling can be turned off on a per application basis using the Vista Program Compatibility properties. Here is a link for more info on how to do that: (Look at the section for “Disable Display Scaling on high DPI settings”.)

How is DPI scaling different from per-application scaling (like IE Zoom?)

A typical application UI is made up of a content window and a frame UI. The frame UI is where the menu items and toolbar buttons are. The content window is the “document view”. For example, in IE the content window is the actual webpage. It turns out the code required to support high DPI scaling for the content windows is the same code required to do the zooming feature. In fact, for the content window, IE8 simply uses the high DPI setting to configure the default zoom factor (see DPI Scaling and Internet Explorer 8 for more details). However, high DPI has the additional side effect of scaling the size of the frame UI. Since most people use the scaling feature to make text larger to be more readable, it makes sense to scale the frame UI as well, since the text in the menu items and toolbar tooltips will also scale. In a sense if there is per-application scaling that is really about the content area, and applications will support that as developers see the customer need. DPI scaling makes the UI elements of all applications render similarly.

Shouldn’t DPI really be used for calibrating the screen (so “an inch is an inch”)?

Some have suggested that we should just use high DPI as a way to calibrate the screen so that the physical size of an object is the same regardless of the display. This makes a ton of sense from a logical perspective. The idea would be to calibrate the display so “in inch is an inch”. We thought about doing this, but the problem is that it does not solve the end user need of wanting to have a way to configure the size of the text and the UI. If we then had a separate “global scale” variable, this would mean that application developers would need to pay attention to both metrics, which would add complexity to the developer story. Furthermore, if a user feels that the UI is too small, should it be up to the developer or the user to set the preference of how big the UI should be? In other words if the designer wants the button to be an inch, but the user wants the button to be 1.5 inches to make it easier to use, who should decide? The way the feature works today, it is up to the user to set their preference, but it is up to the application developer to make sure that the user preference is honored.

Once again, it is really great to see so much interest in high DPI. We certainly have some challenges ahead of us, but in many ways it seems like the ecosystem is ripe for this change. Hopefully this follow up post helped to consolidate some of feedback which we have heard on the previous post and explain some of the complexities of this feature in more detail.

--Ryan Haveson


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