Feature: Interactive Form Dictionary (PDF 1.7 Section 12.7.2) & Appearance Streams (12.5.5) (#25)

Author: tingerrr

examples/forms.rs

@@ -0,0 +1,281 @@
+//! This example shows how to create forms accepted by the most popular readers.
+
+use pdf_writer::types::{
+    ActionType, AnnotationFlags, BorderType, FieldFlags, FieldType, FormActionFlags,
+};
+use pdf_writer::{Content, Finish, Name, Pdf, Rect, Ref, Str, TextStr};
+
+fn main() -> std::io::Result<()> {
+    let mut pdf = Pdf::new();
+
+    // Let's set up our primary font, we'll have to reference it a few times.
+    let text_font_id = Ref::new(1);
+    let text_font_name = Name(b"F1");
+
+    // Here we'll set up our Dingbat font, this is used for symbols such as the
+    // ticks in checkboxes.
+    let symbol_font_id = Ref::new(2);
+    let symbol_font_name = Name(b"F2");
+
+    // One of the most common form field types is the text field. Let's add that
+    // and look at some of the basics of PDF form fields.
+    let text_field_id = Ref::new(4);
+
+    // We start by writing a form field dictionary with an id which we later
+    // need for referencing it.
+    let mut field = pdf.form_field(text_field_id);
+
+    // While the `/T` attribute is optional according to the spec, you should
+    // include it, most readers will only render widget annotations with both
+    // partial name and field type. Next, we set it's value and default value:
+    // - The value is used to store what the user has put into the field.
+    // - The default value is used when resetting the form.
+    field
+        .partial_name(TextStr("text"))
+        .field_type(FieldType::Text)
+        .text_value(TextStr("Hello"))
+        .text_default_value(TextStr("Who reset me"));
+
+    // Our field is a terminal field because it has no children, so it's merged
+    // with its widget annotation. The widget annotation is what declares the
+    // appearance and position in the document, whereas the field defines its
+    // semantic behavior for the document-wide form. The appearance is more
+    // relevant to button fields, we'll see how to cofigure it below.
+    let mut annot = field.into_annotation();
+    annot.rect(Rect::new(108.0, 730.0, 208.0, 748.0));
+
+    // We can pass some fairly simple appearances here, common things such
+    // as the border color and style. This will give out field a purple
+    // underline, keep in mind that this may be drowned out by the viewer's
+    // form highlighting.
+    annot.border_style().style(BorderType::Underline);
+    annot.appearance_characteristics().border_color_rgb(0.0, 0.0, 0.5);
+
+    // The reader will usually provide a default appearance and automatically
+    // highlight form fields. The appearance is relevant for printing however.
+    // While we don't provide an explicit appearnce here, if we did we likely
+    // want this flag to be set.
+    annot.flags(AnnotationFlags::PRINT);
+    annot.finish();
+
+    // A good form has radio buttons. Radio buttons are checkboxes which turn
+    // off when another checkbox is turned on. A group of radio button widget
+    // annotations shares a single radio button field as parent.
+    let radio_group_id = Ref::new(5);
+
+    // The FormXObjects for our checkboxes need bounding boxes, in this case
+    // these are the same size as out rectangles, but within their coordinate
+    // system.
+    let bbox = Rect::new(0.0, 0.0, 30.0, 18.0);
+
+    // We define our three radio buttons, they all have a different appearance
+    // streams, but if they shared the same appearance stream and used the
+    // RADIOS_IN_UNISON flag, then two buttons could refer to the same choice.
+    // This is not widely supported, so we'll simply showcase some normal radio
+    // buttons here.
+    //
+    // NOTE: A reader like Okular will also use on-state name in the default
+    //       appearance.
+    let radios = [
+        (Ref::new(6), Rect::new(108.0, 710.0, 138.0, 728.0), b"ch1"),
+        (Ref::new(7), Rect::new(140.0, 710.0, 170.0, 728.0), b"ch2"),
+        (Ref::new(8), Rect::new(172.0, 710.0, 202.0, 728.0), b"ch3"),
+    ];
+    // First, we define the radio group parent. The children of this field will
+    // be our actual buttons. We can define most of the radio related properties
+    // here.
+    let mut field = pdf.form_field(radio_group_id);
+
+    // We set some flags to get the exact behavior we want.
+    // - FieldFlags::NO_TOGGLE_OFF means that once a button is selected it
+    //   cannot be manually turned off without turning another button on.
+    // - FieldFlags::RADIOS_IN_UNISON ensures that if we have buttons which use
+    //   the same appearance on-state, they'll be toggled in unison with the
+    //   others (although we don't use this here).
+    // Finally we define the children of this field, the widget annotations
+    // which again define appearance and postion of the individual buttons.
+    //
+    // NOTE: by the time of writing this, RADIOS_IN_UNISON does not work
+    //       correctly pdf.js (firefox), okular or evince.
+    field
+        .partial_name(TextStr("radio"))
+        .field_type(FieldType::Button)
+        .field_flags(
+            FieldFlags::RADIO
+                | FieldFlags::NO_TOGGLE_TO_OFF
+                | FieldFlags::RADIOS_IN_UNISON,
+        )
+        .children(radios.map(|(id, _, _)| id));
+    field.finish();
+
+    // For buttons appearances are more relevant when printing as they're
+    // usually not as easy to find as text fields if they have no appearance.
+    let radio_on_appearance_id = Ref::new(9);
+    let radio_off_appearance_id = Ref::new(10);
+
+    // Here we prepare our appearances, the on appearance is a tick and the off
+    // appearance is empty.
+    let mut content = Content::new();
+    content.save_state();
+    content.begin_text();
+    content.set_fill_gray(0.0);
+    content.set_font(symbol_font_name, 14.0);
+    // The character 4 is a tick in this font.
+    content.show(Str(b"4"));
+    content.end_text();
+    content.restore_state();
+
+    let on_stream = content.finish();
+    let mut on_appearance = pdf.form_xobject(radio_on_appearance_id, &on_stream);
+
+    on_appearance.bbox(bbox);
+
+    // We use the symbol font to display the tick, so we need to add it to the
+    // resources of the appearance stream.
+    on_appearance
+        .resources()
+        .fonts()
+        .pair(symbol_font_name, symbol_font_id);
+
+    on_appearance.finish();
+
+    // Our off appearance is empty, we haven't ticked the box.
+    pdf.form_xobject(radio_off_appearance_id, &Content::new().finish())
+        .bbox(bbox);
+
+    // Now we'll write a widget annotation for each button.
+    for (id, rect, state) in radios {
+        // While we create a field here we could directly create widget
+        // annotation too.
+        let mut field = pdf.form_field(id);
+
+        // Each button shares the single parent.
+        field.parent(radio_group_id);
+
+        let mut annot = field.into_annotation();
+        annot.rect(rect).flags(AnnotationFlags::PRINT);
+
+        // This is the state the button starts off with. `/Off` is the off state
+        // and is the same for all radio buttons. The `on` state gets its own
+        // name to distinguish different buttons.
+        annot.appearance_state(Name(b"Off"));
+
+        // Finally we set the appearance dictionary to contain a normal
+        // appearance sub dictionary mapping both on and off state to the
+        // respective FormXObject.
+        {
+            let mut appearance = annot.appearance();
+            appearance.normal().streams().pairs([
+                (Name(state), radio_on_appearance_id),
+                (Name(b"Off"), radio_off_appearance_id),
+            ]);
+        }
+    }
+
+    // Let's add a dropdown menu and allow the user to chose from preconfigrued
+    // options while allowing them to add their own custom option too.
+    let dropdown_id = Ref::new(11);
+    let mut field = pdf.form_field(dropdown_id);
+
+    // Choice fields come in two types, list and combo boxes. A combo box is
+    // also known as a dropdown menu, a list box is like a permanently expanded
+    // drop down menu. The edit flag allows the user to insert their own custom
+    // option.
+    // NOTE: at the time of writing this pdf.js (Firefox) does not allow
+    //       editing of the box
+    field
+        .partial_name(TextStr("choice"))
+        .field_type(FieldType::Choice)
+        .field_flags(FieldFlags::COMBO | FieldFlags::EDIT);
+
+    // Here we define the options the user will be presented with.
+    field.choice_options().options([
+        TextStr("male"),
+        TextStr("female"),
+        TextStr("non-binary"),
+        TextStr("prefer not to say"),
+    ]);
+
+    let mut annot = field.into_annotation();
+    annot
+        .rect(Rect::new(108.0, 690.0, 208.0, 708.0))
+        .flags(AnnotationFlags::PRINT);
+    annot.finish();
+
+    // PDFs can also have push buttons, buttons which retain no state when
+    // pressed. We'll use that to demonstrate form actions. Actions can be
+    // activated on many events, like a change in the input of a field, or
+    // simply the mous cursor moving over the annotation.
+    let button_id = Ref::new(12);
+    let mut field = pdf.form_field(button_id);
+
+    // We set the push button field, otherwise it's interpreted to be a check
+    // box.
+    field
+        .partial_name(TextStr("button"))
+        .field_type(FieldType::Button)
+        .field_flags(FieldFlags::PUSHBUTTON);
+
+    let mut annot = field.into_annotation();
+    annot
+        .rect(Rect::new(108.0, 670.0, 138.0, 688.0))
+        .flags(AnnotationFlags::PRINT);
+
+    // We can quickly give it some basic appearance characteristics like
+    // background and border color.
+    annot.appearance_characteristics().border_color_gray(0.5);
+
+    // Finally, we set the action that is taken when the button is pushed.
+    // It should reset fields in the form, but we must tell it which fields.
+    // By setting the `FormActionFlags::INCLUDE_EXCLUDE` flag, we tell it to
+    // exclude all fields in the we specify and by specifying no fields we
+    // ensure all fields are reset.
+    annot
+        .action()
+        .form_flags(FormActionFlags::INCLUDE_EXCLUDE)
+        .action_type(ActionType::ResetForm)
+        .fields();
+    annot.finish();
+
+    // The PDF catalog contains the form dictionary, telling the reader that
+    // this document contains interactive form fields.
+    let catalog_id = Ref::new(13);
+    let page_tree_id = Ref::new(14);
+    let mut cat = pdf.catalog(catalog_id);
+    cat.pages(page_tree_id);
+
+    // We write all root fields in to the form field dictionary. Root fields are
+    // those which have no parent.
+    cat.form()
+        .fields([text_field_id, radio_group_id, dropdown_id, button_id]);
+    cat.finish();
+
+    // First we create a page which should contain the form fields and write
+    // its resources.
+    let page_id = Ref::new(15);
+    let mut page = pdf.page(page_id);
+    page.media_box(Rect::new(0.0, 0.0, 595.0, 842.0))
+        .parent(page_tree_id)
+        .resources()
+        .fonts()
+        .pair(text_font_name, text_font_id);
+
+    // Now we write each widget annotations refereence into the annotations
+    // array. Those are our terminal fields, those with no children.
+    page.annotations([
+        text_field_id,
+        radios[0].0,
+        radios[1].0,
+        radios[2].0,
+        dropdown_id,
+        button_id,
+    ]);
+    page.finish();
+
+    // Finally we write the font and page tree.
+    pdf.type1_font(text_font_id).base_font(Name(b"Helvetica"));
+    pdf.type1_font(symbol_font_id).base_font(Name(b"ZapfDingbats"));
+    pdf.pages(page_tree_id).kids([page_id]).count(1);
+
+    std::fs::write("target/forms.pdf", pdf.finish())
+}

src/actions.rs

@@ -154,11 +154,26 @@ impl<'a> Fields<'a> {
         self
     }
 
+    /// The indirect references to the fields.
+    pub fn ids(&mut self, ids: impl IntoIterator<Item = Ref>) -> &mut Self {
+        self.array.items(ids);
+        self
+    }
+
     /// The fully qualified name of the field. PDF 1.3+.
     pub fn name(&mut self, name: TextStr) -> &mut Self {
         self.array.item(name);
         self
     }
+
+    /// The fully qualified names of the fields. PDF 1.3+.
+    pub fn names<'b>(
+        &mut self,
+        names: impl IntoIterator<Item = TextStr<'b>>,
+    ) -> &mut Self {
+        self.array.items(names);
+        self
+    }
 }
 
 deref!('a, Fields<'a> => Array<'a>, array);
@@ -219,46 +234,46 @@ bitflags::bitflags! {
         const INCLUDE_NO_VALUE_FIELDS = 2;
         /// Export the fields as HTML instead of submitting as FDF. Ignored if
         /// `SUBMIT_PDF` or `XFDF` are set.
-        const EXPORT_FORMAT = 1 << 3;
+        const EXPORT_FORMAT = 1 << 2;
         /// Field name should be submitted using an HTTP GET request, otherwise
         /// POST. Should only be if `EXPORT_FORMAT` is also set.
-        const GET_METHOD = 1 << 4;
+        const GET_METHOD = 1 << 3;
         /// Include the coordinates of the mouse when submit was pressed. Should
         /// only be if `EXPORT_FORMAT` is also set.
-        const SUBMIT_COORDINATES = 1 << 5;
+        const SUBMIT_COORDINATES = 1 << 4;
         /// Submit field names and values as XFDF instead of submitting an FDF.
         /// Should not be set if `SUBMIT_PDF` is set. PDF1.4+.
-        const XFDF = 1 << 6;
+        const XFDF = 1 << 5;
         /// Include all updates done to the PDF document in the submission FDF
         /// file. Should only be used when `XFDF` and `EXPORT_FORMAT` are not
         /// set. PDF 1.4+.
-        const INCLUDE_APPEND_SAVES = 1 << 7;
+        const INCLUDE_APPEND_SAVES = 1 << 6;
         /// Include all markup annotations of the PDF dcoument in the submission
         /// FDF file. Should only be used when `XFDF` and `EXPORT_FORMAT` are
         /// not set. PDF 1.4+.
-        const INCLUDE_ANNOTATIONS = 1 << 8;
+        const INCLUDE_ANNOTATIONS = 1 << 7;
         /// Submit the PDF file instead of an FDF file. All other flags other
         /// than `GET_METHOD` are ignored if this is set. PDF 1.4+.
-        const SUBMIT_PDF = 1 << 9;
+        const SUBMIT_PDF = 1 << 8;
         /// Convert fields which represent dates into the
         /// [canonical date format](crate::types::Date). The interpretation of
         /// a form field as a date is is not specified in the field but the
         /// JavaScript code that processes it. PDF 1.4+.
-        const CANONICAL_FORMAT = 1 << 10;
+        const CANONICAL_FORMAT = 1 << 9;
         /// Include only the markup annotations made by the current user (the
         /// `/T` entry of the annotation) as determined by the remote server
         /// the form will be submitted to. Should only be used when `XFDF` and
         /// `EXPORT_FORMAT` are not set and `INCLUDE_ANNOTATIONS` is set. PDF
         /// 1.4+.
-        const EXCLUDE_NON_USER_ANNOTS = 1 << 11;
+        const EXCLUDE_NON_USER_ANNOTS = 1 << 10;
         /// Include the F entry in the FDF file.
         /// Should only be used when `XFDF` and `EXPORT_FORMAT` are not set.
         /// PDF 1.4+
-        const EXCLUDE_F_KEY = 1 << 12;
+        const EXCLUDE_F_KEY = 1 << 11;
         /// Include the PDF file as a stream in the FDF file that will be submitted.
         /// Should only be used when `XFDF` and `EXPORT_FORMAT` are not set.
         /// PDF 1.5+.
-        const EMBED_FORM = 1 << 14;
+        const EMBED_FORM = 1 << 13;
     }
 }
 

src/annotations.rs

@@ -4,7 +4,7 @@ use super::*;
 ///
 /// An array of this struct is created by [`Chunk::annotation`].
 pub struct Annotation<'a> {
-    dict: Dict<'a>,
+    pub(crate) dict: Dict<'a>,
 }
 
 writer!(Annotation: |obj| {
@@ -211,7 +211,7 @@ impl<'a> Annotation<'a> {
     /// Start writing the `/MK` dictionary. Only permissible for the subtype
     /// `Widget`.
     pub fn appearance_characteristics(&mut self) -> AppearanceCharacteristics<'_> {
-        self.dict.insert(Name(b"MK")).start()
+        self.insert(Name(b"MK")).start()
     }
 
     /// Write the `/Parent` attribute. Only permissible for the subtype