Draw the faxes

fax_test.go

@@ -0,0 +1,69 @@
+package render
+
+import (
+	"testing"
+
+	"github.com/go-pdfkit/reader"
+)
+
+// TestAFaxIsDrawn guards the dependency, not this package's own code.
+//
+// 67 of the 1 633 real forms in the corpus carry a CCITT-encoded image and 6 of
+// their pages have nothing else on them, so those pages drew blank until
+// go-pdfkit/reader v0.5.0 decoded the filter. Requiring an older reader here
+// would put the blank pages back for anyone who asked only for this package,
+// and nothing in this suite would notice: a package's own tests never see its
+// callers' module graph.
+//
+// The fax is built here rather than committed, so nobody else's scan enters the
+// repository. It is one Group 4 row, three white pixels then five black, coded
+// in horizontal mode: 001 for the mode, then the white run of three and the
+// black run of five from Tables 2 and 3 of ITU-T T.4.
+func TestAFaxIsDrawn(t *testing.T) {
+	bits := "001" + "1000" + "0011"
+	data := make([]byte, (len(bits)+7)/8)
+	for i, c := range bits {
+		if c == '1' {
+			data[i/8] |= 1 << (7 - uint(i%8))
+		}
+	}
+	w := reader.NewWriter("1.7")
+	pagesRef := w.Reserve()
+	img := w.Add(&reader.Stream{Dict: reader.Dict{
+		"Type": reader.Name("XObject"), "Subtype": reader.Name("Image"),
+		"Width": reader.Integer(8), "Height": reader.Integer(1),
+		"ColorSpace": reader.Name("DeviceGray"), "BitsPerComponent": reader.Integer(1),
+		"Filter": reader.Name("CCITTFaxDecode"),
+		"DecodeParms": reader.Dict{"K": reader.Integer(-1),
+			"Columns": reader.Integer(8), "Rows": reader.Integer(1)},
+	}, Raw: data})
+	pageRef := w.Add(reader.Dict{"Type": reader.Name("Page"), "Parent": pagesRef,
+		"MediaBox":  nums(0, 0, 8, 8),
+		"Resources": reader.Dict{"XObject": reader.Dict{"F": img}},
+		"Contents": w.Add(&reader.Stream{Dict: reader.Dict{},
+			Raw: []byte("q 8 0 0 8 0 0 cm /F Do Q")})})
+	w.Put(pagesRef, reader.Dict{"Type": reader.Name("Pages"),
+		"Kids": reader.Array{pageRef}, "Count": reader.Integer(1)})
+	out, err := w.Finish(reader.Dict{"Root": w.Add(reader.Dict{
+		"Type": reader.Name("Catalog"), "Pages": pagesRef})})
+	if err != nil {
+		t.Fatal(err)
+	}
+	d, err := reader.Open(out)
+	if err != nil {
+		t.Fatal(err)
+	}
+	pic, err := Page(d, 1, Options{Scale: 1})
+	if err != nil {
+		t.Fatal(err)
+	}
+	// The right five pixels of the row are black and the left three are white.
+	// A reader that hands back the fax undecoded draws nothing at all, which is
+	// what the six blank pages were.
+	if !isWhite(pic, 1, 4) {
+		t.Errorf("the white part of the fax is not white: %s", pixel(pic, 1, 4))
+	}
+	if !isBlack(pic, 6, 4) {
+		t.Errorf("the black part of the fax is not black: %s", pixel(pic, 6, 4))
+	}
+}

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/go-gfx/gfx v0.10.0
 	github.com/go-opentype/fonts v0.9.0
 	github.com/go-opentype/opentype v0.10.0
-	github.com/go-pdfkit/reader v0.4.2
+	github.com/go-pdfkit/reader v0.5.0
 )
 
 require github.com/go-pdfkit/pdffont v0.3.0

go.sum

@@ -6,5 +6,5 @@ github.com/go-opentype/opentype v0.10.0 h1:cZVMZ3RVkcijXmxlmpqyVkjlNc33aSB2ugKVW
 github.com/go-opentype/opentype v0.10.0/go.mod h1:AOixevJf7XQaH7+WG+OMIOZEbYPXfMqklVk26Y6YTUU=
 github.com/go-pdfkit/pdffont v0.3.0 h1:G5DKcAmsZJ0e17QhSrcUaL7PKEXKjUx4P/iGMl7bAbI=
 github.com/go-pdfkit/pdffont v0.3.0/go.mod h1:bfmNLna1l1CljNX/Utg55YzFylovfmI7sJnvgA3bzKI=
-github.com/go-pdfkit/reader v0.4.2 h1:0/qPShLzdG/roH4i13dwDTHnS7mEBVTaCBGwCZQhOH0=
-github.com/go-pdfkit/reader v0.4.2/go.mod h1:fQFOVfCMUui1AdvD4qhimdyvvNr9KvvJ1S7IuKZjyV8=
+github.com/go-pdfkit/reader v0.5.0 h1:DaJ5C6eKXPRG9Cdu+olA/0KLmsQgyHEC1coteQQuBxU=
+github.com/go-pdfkit/reader v0.5.0/go.mod h1:fQFOVfCMUui1AdvD4qhimdyvvNr9KvvJ1S7IuKZjyV8=