<concept id="GUID-D34DB4A1-1B17-5FAF-A48B-E06D247B0A83" xml:lang="en"><title>Keyboard Mapping DLL Tutorial</title><shortdesc/><prolog><metadata><keywords/></metadata></prolog><conbody>

<p>A keyboard mapping DLL provides a set of lookup tables that the

generic <filepath>ektran.dll</filepath> uses to convert scancodes

to keycodes. A keyboard mapping DLL is implemented in a base port. </p>

to keycodes, so that, given a scancode, the corresponding keycode

can be found. The tables are organized so that there is, in effect,

one set of lookup tables for each likely combination of modifier key

states. <filepath>ektran.dll</filepath> compares the modifier keys

that have been pressed with the stored modifier key state combinations

to decide which set of lookup tables to use. </p>

<p>An outline set of tables is provided in the template port.</p>

<li id="GUID-0C32BD32-0EFD-5622-9C66-2610A3D7F660"><p>The tables are

organized in a hierarchical structure. The start of this hierarchy

is the root table, defined by a <xref href="GUID-F7DFE751-C534-36A8-9B57-9C8417B1BE06.dita"><apiname>SConvTable</apiname></xref> struct.

This contains: </p> <ul>

<li id="GUID-98675F02-D273-5C0D-8AF1-A9F93F8A5AC2"><p>an array of

pointers to nodes, where each node is defined by the <xref href="GUID-3D2F56DB-DD36-3787-8653-C5AC114D69A1.dita"><apiname>SConvTableNode</apiname></xref> struct. Each node corresponds to a specific combination of modifier

key states. </p> </li>

<li id="GUID-8321989A-20FE-58C3-90D0-2D3BE29E11F6"><p>a field containing

the total number of such nodes. </p> </li>

<title>Keyboard Mapping Table</title>

<image href="GUID-FB69F45C-2256-5F2D-8D2C-98C93B865962_d0e385988_href.png" placement="inline"/>

<li id="GUID-C232C328-190D-59F1-A1CB-BC9D736367B0"><p>The combination

of modifier key states that each node represents is encapsulated by

a <xref href="GUID-7D0DE872-AC17-3045-9F97-E25A13B5CFB0.dita"><apiname>TMaskedModifiers</apiname></xref> object. One of these objects

is embedded within each node. </p> <p>A <xref href="GUID-7D0DE872-AC17-3045-9F97-E25A13B5CFB0.dita"><apiname>TMaskedModifiers</apiname></xref> object consists of a mask, and a value for comparison. For example,

if an instance is set to the following: </p> <codeblock id="GUID-E53A8286-C304-50BD-9DB5-81777B48A2E3" xml:space="preserve">iMask = EModifierShift | EModifierCtrl | EModifierFunc

iValue = EModifierShift | EModifierFunc</codeblock> <p>then a match

occurs only for the following combination of modifier key states: </p> <p> <codeph>ctrl</codeph> + <codeph>shift</codeph> + <i>not</i> <codeph>Fn</codeph>  </p> <p>i.e. a match occurs only if <codeph>ctrl</codeph>  <i>and</i> <codeph>shift</codeph> are pressed, and only if <codeph>Fn</codeph> is <i>not</i> pressed. Other modifier keys are ignored,

i.e. it does not matter whether or not they are pressed. </p> <p>In

    }</codeblock> <p>where <codeph>aModifiers</codeph> contains the

modifier key combination to be tested. </p> </li>

<li id="GUID-C147C929-63EE-593B-8CB7-689E5E6E60C2"><p>In principle,

each node represents scancode-to-keycode mappings by associating one

or more <i>pairs</i> (or range) of scancodes with corresponding blocks

of keycodes. Each pair represents an inclusive and contiguous range

of scancodes. </p> <p>Each pair (or range) of scancodes may be "discontiguous"

from the next. </p> <p>The association is made through a table defined

by the <xref href="GUID-35A21F70-F080-364D-8655-5E1781B378EB.dita"><apiname>SConvSubTable</apiname></xref> struct. This has: </p> <ul>

<li id="GUID-9A023CDD-FADF-5641-8DD8-30C11F73E8BE"><p>a <xref href="GUID-DB86A3E5-D118-3A1D-8A76-BEC6111993E8.dita"><apiname>SScanCodeBlockList</apiname></xref> object that contains pointers to a number of <xref href="GUID-F18D6A71-122E-3202-927B-25DCEF1576A4.dita"><apiname>SScanCodeBlock</apiname></xref> objects, each of which contains the start and end values defining

a range of scancodes. </p> </li>

<li id="GUID-AC4820E0-F3D9-547A-9437-964D5A7FE540"><p>a pointer to

a table containing the target keycodes. The target keycodes are arranged

so that successive scancode pairs are associated with successive blocks

of keycodes as the following diagram shows. </p> </li>

<title>Target keycodes</title>

<image href="GUID-DFADEB44-4D57-564F-ABDF-A3CCD38ACABC_d0e386102_href.png" placement="inline"/>

</fig> <p>This means that successive scancodes, for example, from

"A1" through to "B1" are represented by the successive keycodes "keycode

for A1" through to "keycode for B1"; scancode "A2" is represented

by "keycode for A2", which follows "keycode for B1" in the keycode

table. </p> </li>

<li id="GUID-68C8A342-A3D2-5975-82F1-F635E366F741"><p>To allow for

possible reuse of keycode tables, a node can point to more than one <xref href="GUID-35A21F70-F080-364D-8655-5E1781B378EB.dita"><apiname>SConvSubTable</apiname></xref>. The following diagram shows an example of

this: </p> <fig id="GUID-3F5514B5-86E6-52BE-A4C2-38882A1CEACA">

<title>Reusing keycode tables</title>

<image href="GUID-5FDAF564-6BE1-544A-B5C0-E0D6E25D82E7_d0e386123_href.png" placement="inline"/>

<li id="GUID-C6001149-460A-57D4-A9FE-BCB050B49791"><p>If no keycode

can be found that matches the scancode, for a given modifier combination,

then the algorithm returns the <xref href="GUID-76B2E62E-EC09-3CA9-8B2D-EBAC6BF1FFDB.dita"><apiname>EKeyNull</apiname></xref> keycode. </p> </li>

<section id="GUID-A7823728-26DD-4C2F-A97F-91CC4D58B404"><title>See

also</title> <p> <xref href="GUID-EB76FAF8-CD4B-5CB6-9F23-C852ED91866F.dita">Concepts</xref>  </p> </section>