Benchmark paragraph adding. Demonstrates issue #139. (#456)

Couple of TODO comments to where things appear to be slow.

pdf/creator/block.go

@@ -266,6 +266,11 @@ func (blk *Block) translate(tx, ty float64) {
 // drawToPage draws the block on a PdfPage. Generates the content streams and appends to the PdfPage's content
 // stream and links needed resources.
 func (blk *Block) drawToPage(page *model.PdfPage) error {
+
+	// TODO(gunnsth): Appears very wasteful to do this all the time.
+	//        Possibly create another wrapper around model.PdfPage (creator.page) which can keep track of whether
+	//        this has already been done.
+
 	// Check if Page contents are wrapped - if not wrap it.
 	content, err := page.GetAllContentStreams()
 	if err != nil {
@@ -374,6 +379,10 @@ func (blk *Block) mergeBlocks(toAdd *Block) error {
 func mergeContents(contents *contentstream.ContentStreamOperations, resources *model.PdfPageResources,
 	contentsToAdd *contentstream.ContentStreamOperations, resourcesToAdd *model.PdfPageResources) error {
 
+	// TODO(gunnsth): It seems rather expensive to mergeContents all the time. A lot of repetition.
+	//    It would be more efficient to perform the merge at the very and when we have all the "blocks"
+	//    for each page.
+
 	// To properly add contents from a block, we need to handle the resources that the block is
 	// using and make sure it is accessible in the modified Page.
 	//

pdf/creator/paragraph_test.go

@@ -0,0 +1,35 @@
+/*
+ * This file is subject to the terms and conditions defined in
+ * file 'LICENSE.md', which is part of this source code package.
+ */
+
+package creator
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func benchmarkParagraphAdding(b *testing.B, loops int) {
+	for n := 0; n < b.N; n++ {
+		c := New()
+		for i := 0; i < loops; i++ {
+			p := c.NewParagraph(fmt.Sprintf("Paragraph %d - %d", n, i))
+			err := c.Draw(p)
+			require.NoError(b, err)
+		}
+
+		var buf bytes.Buffer
+		err := c.Write(&buf)
+		require.NoError(b, err)
+	}
+}
+
+// Benchmark adding multiple paragraphs and writing out.
+// Check the effects of varying number of paragraphs written out.
+func BenchmarkParagraphAdding1(b *testing.B)   { benchmarkParagraphAdding(b, 1) }
+func BenchmarkParagraphAdding10(b *testing.B)  { benchmarkParagraphAdding(b, 10) }
+func BenchmarkParagraphAdding100(b *testing.B) { benchmarkParagraphAdding(b, 100) }