A Game in XForms

Steven Pemberton, CWI Amsterdam

Contents

Youngest: How do you program a game?

Me: What sort of game?

Youngest:

Take some data

Four rows of four cells

<instance>
  <game xmlns="">
    <row><cell>1</cell><cell>5</cell><cell>8</cell><cell>12</cell></row>
    <row><cell>2</cell><cell>6</cell><cell>9</cell><cell>13</cell></row>
    <row><cell>3</cell><cell>7</cell><cell>10</cell><cell>14</cell></row>
    <row><cell>4</cell><cell>.</cell><cell>11</cell><cell>15</cell></row>
  </game>
</instance>

Display it

Four rows of four cells

<instance>
  <game xmlns="">
    <row><cell>1</cell><cell>5</cell><cell>8</cell><cell>12</cell></row>
    <row><cell>2</cell><cell>6</cell><cell>9</cell><cell>13</cell></row>
    <row><cell>3</cell><cell>7</cell><cell>10</cell><cell>14</cell></row>
    <row><cell>4</cell><cell>.</cell><cell>11</cell><cell>15</cell></row>
  </game>
</instance>

<repeat ref="row"> 
    <repeat ref="cell" >
        <output value="."/>
    </repeat>
</repeat>

Display it

Four rows of four cells

<instance>
  <game xmlns="">
    <row><cell>1</cell><cell>5</cell><cell>8</cell><cell>12</cell></row>
    <row><cell>2</cell><cell>6</cell><cell>9</cell><cell>13</cell></row>
    <row><cell>3</cell><cell>7</cell><cell>10</cell><cell>14</cell></row>
    <row><cell>4</cell><cell>.</cell><cell>11</cell><cell>15</cell></row>
  </game>
</instance>

<repeat ref="row"> 
    <repeat ref="cell" >
        <output value="."/>
    </repeat>
</repeat>

Add a dash of CSS.

Result

Of course, this doesn't do anything yet.

Add interaction

<repeat ref="row"> 
    <repeat ref="cell" >
        <trigger appearance="minimal">
            <label><output value="."/></label>
        </trigger>
    </repeat>
</repeat>

trigger is the XForms version of HTML's button, but XForms tries to be device-neutral.

"appearance="minimal"" means it isn't displayed as a button.

It still doesn't do anything.

Add an action

<repeat ref="row"> 
    <repeat ref="cell" >
        <trigger appearance="minimal">
            <label><output value="."/></label>
            <action ev:event="DOMActivate">
            ...
            </action>
        </trigger>
    </repeat>
</repeat>

This says to respond to the trigger being activated (eg a click).

Add in the action

<repeat ref="row"> 
    <repeat ref="cell" >
        <trigger appearance="minimal">
            <label><output value="."/></label>
            <action ev:event="DOMActivate">
                <setvalue ref="//cell[.='.']" value="context()"/>
                <setvalue ref="." value="'.'"/>
            </action>
        </trigger>
    </repeat>
</repeat>

If you click on any of the squares, it will swap the value there with the square holding "."

Result

Add a condition

We only want to allow swapping the empty square with an adjacent one.

Add a condition to the action.

<repeat ref="row"> 
    <repeat ref="cell" >
        <trigger appearance="minimal">
            <label><output value="."/></label>
            <action ev:event="DOMActivate" if="...">
                <setvalue ref="//cell[.='.']" value="context()"/>
                <setvalue ref="." value="'.'"/>
            </action>
        </trigger>
    </repeat>
</repeat>

Condition

Only do the action if the next or previous cell, or the cell at the same position in the previous/next row is ".".

following-sibling::cell[1]='.' or
preceding-sibling::cell[1]='.' or
 ../following-sibling::row[1]/
cell[1+count(context()/preceding-sibling::cell)]='.' or 
 ../preceding-sibling::row[1]/
cell[1+count(context()/preceding-sibling::cell)]='.'

Result

"It would be more fun if it was like a jigsaw"

Easy

<trigger appearance="minimal">
    <label><output mediatype="image/*" value="."/></label>

This says: Interpret the value as a URL and display it as an image.

Only problem: you may not have a file called ".".

Easy

<trigger appearance="minimal">
   <label><output mediatype="image/*"
                  value="if(.='.', 'blank', .)" />
   </label>
</trigger>

Result