Transparent pixmaps in Mapserver 4.4.1

[Camden Daily]

The problem ended up being with the way I was drawing my points in
mapscript.  I had been drawing the image first, and then placing the
points over it like this:

// draw our image without the points
$image = $map->draw();
// add our point to the map
$point->draw($map, $point_layer, $image, 0, "");

But I guess since the rest of the map was drawn first, the transparent
point symbols wouldn't actually be made transparent.

I fixed it by instead creating a dummy layer and adding my points as
features to it and then drawing the map, like this:

// create a temp layer to hold our points
$point_layer = ms_newLayerObj($map);
$point_layer->set("name", "markers");
$point_layer->set("type", MS_LAYER_POINT);
$point_layer->set("status", MS_ON);
// 1000 is the value used to set transparency to "alpha"
$point_layer->set("transparency", 1000);

// create a class and style for this layer
$point_class = ms_newClassObj($point_layer);
$point_style = ms_newStyleObj($point_class);

// set the symbol we'll use for our points
$point_symbol = $map->getSymbolByName("house");
$point_style->set("symbol", $point_symbol);
$point_style->set("size", 40);

$point_line = ms_newLineObj();
$point_line->add($point);
$point_shape = ms_newShapeObj(MS_SHAPE_POINT);
$point_shape->add($point_line);
$point_layer->addFeature($point_shape);

// draw our image
$image = $map->draw();

And it works like a charm!  Thanks for all the help Sean.  I entered a
mapscript bugzilla about the alpha value, and it appears MS_GD_ALPHA
has been added as the new constant value for setting the transparency
level.