Nowadays, all PocketPC’s support ClearType rendering. ClearType is Microsoft’s name for sub-pixel rendering, a technology that makes text appear “smoother” by using a specific property of LCD displays. However, ClearType usually works only in portrait mode – while a hack is available for enabling landscape mode, I think that this usually doesn’t pay out.

In order to understand why I’m skeptical, we need to take a deeper look at how LCD screens actually work. Feel free to follow me along(yes, the figures are hand-drawn; nope, they can’t be given away…they already have a new owner):

First of all, here, we see a LCD screen(2×2 pixel only). As you can see, it is made up of pixels(points), who are then made up of so-called sub-pixels. A sub-pixel is like a small red, green or blue bulb that can be dimmed in steps. Now, a pixel consists of one R, G and B subpixel; together, they can create every color:
0a ClearType and landscape mode   why it CANNOT work

Now, a regular LCD would render a line from left bottom to top right as shown below. If the pixels are big enough, a “step” effect will be visible:
1a ClearType and landscape mode   why it CANNOT work

And this is where ClearType locks in(explanation simplified). The program enables sub-pixels adjacent to the line(shown in blue) and possibly also dims corresponding sub-pixels at the other side in order to make the steps less prominent:
2a ClearType and landscape mode   why it CANNOT work

So, a line that goes mostly perpendicular to the sub-pixel grid(horizontal) and has just a light slant to the left or the right, benefits a lot from ClearType(look at the average font…most lines are vertical). A line that goes parallel to the sub-pixel grid doesn’t benefit at all.

As said before, most fonts are made up of entirely vertical lines. In portrait mode, the sub-pixel grid is horizontal. Thus, most lines do benefit. However, once your PocketPC is in landscape mode, the sub-pixel grid AND most of the lines are arranged. In landscape mode, ClearType can’t do much, as most of the lines can’t really be optimized. Thus, Microsoft chose to disable the feature…probably to save CPU performance…

Now that we have the physical and electronics background, please let me know what you think! Do you like ClearType’s output when in landscape mode?

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One Response to “ClearType and landscape mode – why it CANNOT work”

  1. You said:
    ClearType usually works only in portrait mode”

    I know this is an old post, but isnt it the OPPOSITE of that? In other words, it only works in Landscape mode?

    That’s what everyone else says.

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