Form structure for the image scale form.
Note that this is not a complete form, it only contains the portion of the form for configuring the scale options. Therefore it does not not need to include metadata about the effect, nor a submit button.
$data: The current configuration for this scale effect.
function image_scale_form($data) {
$form = image_resize_form($data);
$form['#element_validate'] = array(
'image_effect_scale_validate',
);
$form['width']['#required'] = FALSE;
$form['height']['#required'] = FALSE;
$form['upscale'] = array(
'#type' => 'checkbox',
'#default_value' => isset($data['upscale']) ? $data['upscale'] : 0,
'#title' => t('Allow Upscaling'),
'#description' => t('Let scale make images larger than their original size'),
);
return $form;
}