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<concept id="GUID-0EBE5733-A267-5F4A-85AD-87C3ECF80731" xml:lang="en"><title>Dynamic

Resolution Switching</title><shortdesc>ScreenPlay provides support for externally connected displays,

such as TV-out. Previous versions of Symbian and the non-ScreenPlay variant

consider the size of all displays to be fixed, assuming them to be built into

the phone. However, for High-Definition Multimedia Interface (HDMI) and composite

video connectors, there is a range of resolutions that can change dynamically.

ScreenPlay provides an optional feature that supports switching between resolutions

at runtime. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<p> <b>Variant</b>: <xref href="GUID-D93978BE-11A3-5CE3-B110-1DEAA5AD566C.dita">ScreenPlay</xref>. </p>

<section id="GUID-374864AA-3757-4BD9-A5EB-4AC0E6DDD198"><title>The pre-ScreenPlay background</title> <p>Early devices typically

had a screen size of 220 x 176 pixels. Over time, these were followed by higher

resolution screens, such as 440 x 252 pixels. Applications that were designed

for 220 x 176 pixel screens could run on 440 x 252 pixel screens because the

Window Server simply scaled the pixels by a factor of two. </p> <p>However,

this approach did not work when phones with 320 x 240 pixel screens were introduced,

because each axis required a different scaling factor. Symbian introduced

the <b>screen mode</b> feature to handle this and similar use cases. Device

creators define in the <xref href="GUID-1D529BDC-6665-58E2-AB3F-7023D8A84F69.dita">wsini.ini

file</xref> a number of screen modes for each physical screen on the device.

For each screen mode the device creator defines parameters to control the

offset from the top left corner of the screen, the height and width in both

pixels and twips, <i>X</i> and <i>Y</i> axis scaling factors and so on. The

Window Server uses these to position and scale old applications so that they

can run on new phones with higher resolutions, as shown in the following diagram

(which is not drawn to scale). The screen mode is still used in the same way

in the <xref href="GUID-F64E6551-670E-5E12-8103-DE504D3EC94F.dita">non-ScreenPlay

variant</xref>. </p> <fig id="GUID-FF86B974-1B1E-5EE1-A88A-9CD11B213A9B">

<title>The screen mode enables old applications to run on new            

 phones with higher resolutions            </title>

<image href="GUID-AFC49653-78E6-5639-911C-E02AEB08AFFC_d0e191929_href.png" placement="inline"/>

</fig> <p>There are several similar use cases, such as swapping between portrait

and landscape orientations and flip phones that have a flap that, when closed,

partially obscures the main screen. The Window Server uses the screen mode

parameters to display applications differently depending on whether the phone

is in portrait or landscape orientation and whether the flap is open or closed.

The screen mode represents the area that is presented to the application and

is available to application developers through <xref href="GUID-30479BE3-296E-3B4D-914D-B080ABD733E4.dita#GUID-30479BE3-296E-3B4D-914D-B080ABD733E4/GUID-8E1B5729-FD1C-3D4A-AC73-C6364E7D5BBF"><apiname>CWsScreenDevice::SizeInPixels()</apiname></xref>. </p> <p>Defining

the screen modes in the <xref href="GUID-1D529BDC-6665-58E2-AB3F-7023D8A84F69.dita">wsini.ini

file</xref> in this way means that all possible screen sizes and resolutions

must be fixed and known at ROM building time. This approach has limitations

when working with technologies such as HDMI and composite video connectors,

where there is a very wide range of possible resolutions that may not be known

until runtime. </p> </section>

<section id="GUID-139F6C69-85CD-4796-AE8D-A48EEAEB5294"><title>The ScreenPlay approach</title> <p>In ScreenPlay the actual

resolution of the full composition/display area can be determined at runtime.

The full UI area is mapped to fill this display area but may be a lower virtual

resolution, which is scaled. The render stage chain handles the

scaling and positioning of applications and any external surfaces within the

UI, and the composition engine performs the scaling of the pixel data to the

actual display area at physical resolution. This has the advantage that the

scaling can be handled by the graphics acceleration hardware, if it is available. </p> <p>Another

advantage of this approach is that it enables dynamic scaling of the pixels.

Usually pixels are square on a mobile phone display, but not square on many

external displays. When the square pixels from the device are displayed on

such a display, they may need to be scaled by different arbitrary factors

on each axis. This is called <b>anisotropic scaling</b>. In contrast, <b>isotropic

scaling</b> means that both pixel axes are scaled by the same arbitrary factor. </p> <p>The

following diagram illustrates how the full UI area is mapped to fill the display/composition

area. The application's area (which corresponds to the screen mode) is referred

to as the <b>application extent</b> in ScreenPlay. </p> <fig id="GUID-724DB4EE-1F45-58D9-889C-B42ECEE7208D">

<title>Coordinate spaces in ScreenPlay            </title>

<image href="GUID-A719FDFA-903B-5340-AA47-9E5B22DBB253_d0e191975_href.png" placement="inline"/>

</fig> <p>ScreenPlay handles application sizing and positioning in a fundamentally

different way from the non-ScreenPlay variant. Using a fixed offset to position

the application within the screen is inadequate when connecting to an external

HDMI display, for example, when the resolution may not be known until runtime.

For example, the offset designed for a QVGA display does not position the

application correctly in a higher resolution display, as shown in the following

diagram, where the red cross indicates the offset for a QVGA display. </p> <fig id="GUID-A2816D08-B61F-5605-B6AF-A9D186F6BED5">

<title>A fixed offset and several display resolutions (not drawn         

    to scale)            </title>

<image href="GUID-B2E63B13-7B72-5CBF-ACD0-1F2D2E1EEF19_d0e191986_href.png" placement="inline"/>

</fig> <p>In ScreenPlay there is no scaling of the application extent relative

to the full UI area—there is always a 1:1 pixel correspondence between them.

In addition, although supported, the screen mode offset is not necessarily

used. Instead, the render stage chain selects an appropriate virtual resolution

and handles the positioning—for example, centering it and using a best fit

algorithm so that it takes up as much of the screen as possible or using the

offset as a minimum margin size. The device creator can choose how to implement

this in the render stages. In order to position the application correctly

within the UI area, the Window Server gets the positioning information from

the first render stage in the chain when the configuration or screen mode

changes. </p> <p>ScreenPlay supports fixed screen modes in the <xref href="GUID-1D529BDC-6665-58E2-AB3F-7023D8A84F69.dita">wsini.ini

file</xref>, although the scaling parameters are not used. However, the screen

mode width and height in pixels and twips when specified and used together,

provide the pixel aspect ratio. In order to maintain backwards compatibility,

render stages should respect this aspect ratio whenever possible. </p> <p>It

is possible for applications to determine and draw to the UI area outside

the application extent using the APIs described below. However, <b>dynamic

screen modes</b> provide an alternative mechanism for existing applications

to access the full UI area. This is particularly suitable for HDMI and similar

technologies where the resolution may not be known until runtime. To use this

approach, the device creator must define one or two screen modes in the <xref href="GUID-1D529BDC-6665-58E2-AB3F-7023D8A84F69.dita">wsini.ini file</xref> and

set their height and width in pixels to -1. One dynamic screen mode then represents

the current display configuration and the other one, if present, represents

the configuration when the screen is rotated by 90º or 270º. Using dynamic

screen modes means that the display configuration can be changed at runtime

according to the hardware that is available and detected by the composition

engine. </p> <p>When a dynamic screen mode is used, the application extent

always fills the full UI space and the area returned by <xref href="GUID-30479BE3-296E-3B4D-914D-B080ABD733E4.dita#GUID-30479BE3-296E-3B4D-914D-B080ABD733E4/GUID-8E1B5729-FD1C-3D4A-AC73-C6364E7D5BBF"><apiname>CWsScreenDevice::SizeInPixels()</apiname></xref> always

matches the actual resolution that is in use. </p>  </section>

</conbody><related-links>

<link href="GUID-99BC101A-9466-59EE-B5C9-7622BAF6E6FF.dita"><linktext>Graphics

Concepts</linktext></link>

</related-links></concept>