Add content stream compression

Closes #14

Author: reknih

src/defer.rs

@@ -238,7 +238,8 @@ pub(crate) fn write_masks(tree: &Tree, writer: &mut PdfWriter, ctx: &mut Context
 
             let content = content_stream(&mask_node, writer, ctx);
 
-            let mut group = form_xobject(writer, gp.reference, &content, gp.bbox, true);
+            let mut group =
+                form_xobject(writer, gp.reference, &content, gp.bbox, ctx.compress, true);
 
             if let Some(matrix) = gp.matrix {
                 group.matrix(matrix);

src/lib.rs

@@ -39,7 +39,7 @@ use std::collections::HashMap;
 
 use pdf_writer::types::ProcSet;
 use pdf_writer::writers::{ColorSpace, ExponentialFunction, FormXObject, Resources};
-use pdf_writer::{Content, Finish, Name, PdfWriter, Rect, Ref, TextStr, Writer};
+use pdf_writer::{Content, Filter, Finish, Name, PdfWriter, Rect, Ref, TextStr, Writer};
 use usvg::{NodeExt, NodeKind, Opacity, Stop, Tree};
 
 mod defer;
@@ -91,11 +91,23 @@ pub struct Options {
     ///
     /// _Default:_ `72.0`.
     pub dpi: f64,
+    /// Whether the content streams should be compressed.
+    ///
+    /// The smaller PDFs generated by this are generally more practical but it
+    /// increases runtime a bit.
+    ///
+    /// _Default:_ `true`.
+    pub compress: bool,
 }
 
 impl Default for Options {
     fn default() -> Self {
-        Options { viewport: None, aspect: None, dpi: 72.0 }
+        Options {
+            viewport: None,
+            aspect: None,
+            dpi: 72.0,
+            compress: true,
+        }
     }
 }
 
@@ -137,11 +149,13 @@ struct Context<'a> {
     /// The mask that needs to be applied at the start of a path drawing
     /// operation.
     initial_mask: Option<String>,
+    /// Whether the content streas should be compressed.
+    compress: bool,
 }
 
 impl<'a> Context<'a> {
     /// Create a new context.
-    fn new(tree: &'a Tree, bbox: &'a Rect, c: CoordToPdf) -> Self {
+    fn new(tree: &'a Tree, compress: bool, bbox: &'a Rect, c: CoordToPdf) -> Self {
         Self {
             tree,
             bbox,
@@ -159,6 +173,7 @@ impl<'a> Context<'a> {
             pending_groups: HashMap::new(),
             checkpoints: vec![],
             initial_mask: None,
+            compress,
         }
     }
 
@@ -253,7 +268,7 @@ pub fn convert_str(src: &str, options: Options) -> Result<Vec<u8>, usvg::Error>
 /// Convert a [`usvg` tree](Tree) to a standalone PDF buffer.
 pub fn convert_tree(tree: &Tree, options: Options) -> Vec<u8> {
     let (c, bbox) = get_sizings(tree, &options);
-    let mut ctx = Context::new(&tree, &bbox, c);
+    let mut ctx = Context::new(&tree, options.compress, &bbox, c);
 
     let mut writer = PdfWriter::new();
     let catalog_id = ctx.alloc_ref();
@@ -282,7 +297,13 @@ pub fn convert_tree(tree: &Tree, options: Options) -> Vec<u8> {
     resources.finish();
     page.finish();
 
-    writer.stream(content_id, &content);
+    let mut stream = writer.stream(content_id, &content);
+    if ctx.compress {
+        stream.filter(Filter::FlateDecode);
+    }
+
+    stream.finish();
+
     writer.document_info(ctx.alloc_ref()).producer(TextStr("svg2pdf"));
 
     writer.finish()
@@ -381,7 +402,7 @@ pub fn convert_tree_into(
     id: Ref,
 ) -> Ref {
     let (c, bbox) = get_sizings(tree, &options);
-    let mut ctx = Context::new(&tree, &bbox, c);
+    let mut ctx = Context::new(&tree, options.compress, &bbox, c);
 
     ctx.next_id = id.get() + 1;
 
@@ -403,6 +424,10 @@ pub fn convert_tree_into(
         0.0,
     ]);
 
+    if ctx.compress {
+        xobject.filter(Filter::FlateDecode);
+    }
+
     let mut resources = xobject.resources();
     ctx.pop(&mut resources);
 
@@ -483,7 +508,9 @@ fn content_stream<'a>(
         }
     }
 
-    content.finish()
+    let res = content.finish();
+
+    if ctx.compress { deflate(&res) } else { res }
 }
 
 /// Draw a clipping path into a content stream.
@@ -695,11 +722,16 @@ fn form_xobject<'a>(
     reference: Ref,
     content: &'a [u8],
     bbox: Rect,
+    compress: bool,
     has_color: bool,
 ) -> FormXObject<'a> {
     let mut form = writer.form_xobject(reference, content);
     form.bbox(bbox);
 
+    if compress {
+        form.filter(Filter::FlateDecode);
+    }
+
     let mut group = form.group();
     group.transparency();
     group.isolated(true);
@@ -716,6 +748,12 @@ fn form_xobject<'a>(
     form
 }
 
+/// Compress data with the DEFLATE algorithm.
+fn deflate(data: &[u8]) -> Vec<u8> {
+    const COMPRESSION_LEVEL: u8 = 6;
+    miniz_oxide::deflate::compress_to_vec_zlib(data, COMPRESSION_LEVEL)
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

src/render.rs

@@ -23,9 +23,9 @@ use super::{
     apply_clip_path, apply_mask, content_stream, form_xobject, Context, Options,
     RgbColor, SRGB,
 };
-use crate::convert_tree_into;
 use crate::defer::{PendingGS, PendingGradient};
 use crate::scale::CoordToPdf;
+use crate::{convert_tree_into, deflate};
 
 /// Write the appropriate instructions for a node into the content stream.
 ///
@@ -291,8 +291,14 @@ fn render_path_partial(
     // Write the Form XObject if there was a gradient with alpha values.
     if let Some((xobj_content, path_no)) = xobj_content {
         let path_ref = ctx.alloc_ref();
-        let data = xobj_content.finish();
-        let mut form = form_xobject(writer, path_ref, &data, pdf_bbox, true);
+        let data = if ctx.compress {
+            deflate(&xobj_content.finish())
+        } else {
+            xobj_content.finish()
+        };
+
+        let mut form =
+            form_xobject(writer, path_ref, &data, pdf_bbox, ctx.compress, true);
         let mut resources = form.resources();
         ctx.pop(&mut resources);
         ctx.pending_xobjects.push((path_no, path_ref));
@@ -379,6 +385,7 @@ fn prep_shading(
         &shading_content,
         ctx.c.pdf_rect(bbox),
         false,
+        false,
     );
 
     let mut resources = smask_form.resources();
@@ -479,6 +486,10 @@ fn prep_pattern(
         .x_step(pdf_rect.x2 - pdf_rect.x1)
         .y_step(pdf_rect.y2 - pdf_rect.y1);
 
+    if ctx.compress {
+        pdf_pattern.filter(Filter::FlateDecode);
+    }
+
     let mut resources = pdf_pattern.resources();
     ctx.pop(&mut resources);
     resources.finish();
@@ -509,7 +520,14 @@ impl Render for usvg::Group {
 
         // Every group is an isolated transparency group, it needs to be painted
         // onto its own canvas.
-        let mut form = form_xobject(writer, group_ref, &child_content, pdf_bbox, true);
+        let mut form = form_xobject(
+            writer,
+            group_ref,
+            &child_content,
+            pdf_bbox,
+            ctx.compress,
+            true,
+        );
         let mut resources = form.resources();
         ctx.pop(&mut resources);
 
@@ -691,6 +709,7 @@ impl Render for usvg::Image {
                         viewport: Some((rect.width(), rect.height())),
                         aspect: Some(self.view_box.aspect),
                         dpi: ctx.c.dpi(),
+                        compress: ctx.compress,
                     };
 
                     ctx.next_id = convert_tree_into(tree, opt, writer, image_ref).get();