Add DPI option, issue #52

cbconvert.go

@@ -39,6 +39,8 @@ type Options struct {
 	Height int
 	// Best fit for required width and height
 	Fit bool
+	// Document rendering resolution in DPI (PDF, EPUB, etc.); 0 uses the default
+	DPI int
 	// 0=NearestNeighbor, 1=Box, 2=Linear, 3=MitchellNetravali, 4=CatmullRom, 6=Gaussian, 7=Lanczos
 	Filter int
 	// Do not convert the cover image
@@ -178,6 +180,7 @@ func (o Options) Args() []string {
 	num("width", o.Width, def.Width)
 	num("height", o.Height, def.Height)
 	flag("fit", o.Fit)
+	num("dpi", o.DPI, def.DPI)
 	str("format", o.Format, def.Format)
 	str("archive", o.Archive, def.Archive)
 	num("zip-level", o.ZipLevel, def.ZipLevel)
@@ -203,6 +206,15 @@ func (o Options) Args() []string {
 	return args
 }
 
+// renderDPI returns the document rendering resolution, falling back to 300 when unset.
+func (c *Converter) renderDPI() float64 {
+	if c.Opts.DPI > 0 {
+		return float64(c.Opts.DPI)
+	}
+
+	return 300
+}
+
 // Cancel cancels the operation.
 func (c *Converter) Cancel() {
 	if c.OnCancel != nil {

cbconvert_convert.go

@@ -48,7 +48,7 @@ func (c *Converter) convertDocument(ctx context.Context, fileName string) error
 			return fmt.Errorf("convertDocument: %w", ctx.Err())
 		}
 
-		img, err := doc.Image(n)
+		img, err := doc.ImageDPI(n, c.renderDPI())
 		if err != nil {
 			return fmt.Errorf("convertDocument: %w", err)
 		}

cbconvert_cover.go

@@ -52,7 +52,7 @@ func (c *Converter) coverDocument(fileName string) (image.Image, error) {
 	}
 	defer doc.Close()
 
-	img, err := doc.Image(0)
+	img, err := doc.ImageDPI(0, c.renderDPI())
 	if err != nil {
 		return nil, fmt.Errorf("coverDocument: %w", err)
 	}

cbconvert_test.go

@@ -114,16 +114,52 @@ func TestArgs(t *testing.T) {
 	opts.Effort = 4
 	opts.Lossless = true
 	opts.Width = 1200
+	opts.DPI = 150
 	opts.Grayscale = true
 	opts.OutDir = "/out"
 
 	got := strings.Join(opts.Args(), " ")
-	want := "--width 1200 --format webp --quality 90 --effort 4 --lossless --grayscale --outdir /out"
+	want := "--width 1200 --dpi 150 --format webp --quality 90 --effort 4 --lossless --grayscale --outdir /out"
 	if got != want {
 		t.Errorf("Args() = %q, want %q", got, want)
 	}
 }
 
+func TestConvertDPI(t *testing.T) {
+	tmpDir, err := os.MkdirTemp(os.TempDir(), "cbc")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	dims := func(dpi int) int {
+		opts := NewOptions()
+		opts.OutDir = tmpDir
+		opts.DPI = dpi
+
+		conv := New(opts)
+
+		files, err := conv.Files([]string{"testdata/test.pdf"})
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		for _, file := range files {
+			if err := conv.Convert(file); err != nil {
+				t.Fatal(err)
+			}
+		}
+
+		return firstPage(t, conv, filepath.Join(tmpDir, "test.cbz")).Bounds().Dx()
+	}
+
+	low := dims(150)
+	high := dims(600)
+	if low >= high {
+		t.Errorf("higher DPI should render larger pages: 150dpi=%d, 600dpi=%d", low, high)
+	}
+}
+
 func TestConvertResize(t *testing.T) {
 	tmpDir, err := os.MkdirTemp(os.TempDir(), "cbc")
 	if err != nil {

cmd/cbconvert-gui/main.go

@@ -77,6 +77,7 @@ var settings = []setting{
 	{"Suffix", kindStr, ""},
 	{"Width", kindStr, ""},
 	{"Height", kindStr, ""},
+	{"DPI", kindStr, "Default"},
 	{"Size", kindInt, "0"},
 	{"Quality", kindInt, "75"},
 	{"Effort", kindInt, "0"},
@@ -203,6 +204,7 @@ func options() cbconvert.Options {
 	opts.Format = strings.ToLower(iup.GetHandle("Format").GetAttribute("VALUESTRING"))
 	opts.Width = iup.GetHandle("Width").GetInt("VALUE")
 	opts.Height = iup.GetHandle("Height").GetInt("VALUE")
+	opts.DPI = dpiValue(iup.GetHandle("DPI").GetAttribute("VALUE"))
 	opts.Fit = iup.GetHandle("Fit").GetAttribute("VALUE") == "ON"
 	opts.Filter = iup.GetHandle("Filter").GetInt("VALUE") - 1
 	opts.Quality = iup.GetHandle("Quality").GetInt("VALUE")
@@ -362,6 +364,15 @@ func zipLevel(value string) int {
 	}
 }
 
+func dpiValue(value string) int {
+	dpi, err := strconv.Atoi(strings.TrimSpace(value))
+	if err != nil {
+		return 0
+	}
+
+	return dpi
+}
+
 func profileGroup(name string) string {
 	return "Profile:" + name
 }
@@ -846,6 +857,21 @@ func tabs() iup.Ihandle {
 			iup.Text().SetAttributes(`SPIN=YES, SPINMAX=2048, VISIBLECOLUMNS=4, MASK="/d*"`).SetHandle("Size").
 				SetAttributes(`TIP="Process only files larger than minimum size"`),
 		),
+		iup.Vbox(
+			iup.Label("Document DPI:"),
+			iup.List().SetAttributes(map[string]string{
+				"DROPDOWN":       "YES",
+				"EDITBOX":        "YES",
+				"VISIBLECOLUMNS": "6",
+				"VALUE":          "Default",
+				"1":              "Default",
+				"2":              "150",
+				"3":              "300",
+				"4":              "600",
+				"5":              "1200",
+			}).SetHandle("DPI").
+				SetAttribute("TIP", "Resolution for rendering documents (PDF, EPUB, etc.); Default is 300"),
+		),
 		iup.Space().SetAttributes("EXPAND=HORIZONTAL"),
 	).SetHandle("VboxInput").SetAttributes("NGAP=10")
 

cmd/cbconvert/main.go

@@ -175,6 +175,7 @@ func parseFlags() (cbconvert.Options, []string) {
 	convert.IntVar(&opts.Width, "width", 0, "Image width")
 	convert.IntVar(&opts.Height, "height", 0, "Image height")
 	convert.BoolVar(&opts.Fit, "fit", false, "Best fit for required width and height")
+	convert.IntVar(&opts.DPI, "dpi", 0, "Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300)")
 	convert.StringVar(&opts.Format, "format", "jpeg", "Image format, valid values are jpeg, png, tiff, bmp, webp, avif, jxl")
 	convert.StringVar(&opts.Archive, "archive", "zip", "Archive format, valid values are zip, tar")
 	convert.IntVar(&opts.ZipLevel, "zip-level", -1, "ZIP compression level, 0 disables compression, 1-9 sets deflate level (1 fastest, 9 smallest), -1 uses the default")
@@ -202,6 +203,7 @@ func parseFlags() (cbconvert.Options, []string) {
 	cover.IntVar(&opts.Width, "width", 0, "Image width")
 	cover.IntVar(&opts.Height, "height", 0, "Image height")
 	cover.BoolVar(&opts.Fit, "fit", false, "Best fit for required width and height")
+	cover.IntVar(&opts.DPI, "dpi", 0, "Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300)")
 	cover.StringVar(&opts.Format, "format", "jpeg", "Image format, valid values are jpeg, png, tiff, bmp, webp, avif")
 	cover.IntVar(&opts.Quality, "quality", 75, "Image quality")
 	cover.IntVar(&opts.Effort, "effort", -1, "Encoder speed/effort, format-specific (webp method 0-6, avif speed 0-10, jxl effort 1-10), -1 uses the format default")
@@ -216,6 +218,7 @@ func parseFlags() (cbconvert.Options, []string) {
 	thumbnail.IntVar(&opts.Width, "width", 0, "Image width")
 	thumbnail.IntVar(&opts.Height, "height", 0, "Image height")
 	thumbnail.BoolVar(&opts.Fit, "fit", false, "Best fit for required width and height")
+	thumbnail.IntVar(&opts.DPI, "dpi", 0, "Document rendering resolution in DPI (PDF, EPUB, etc.), 0 uses the default (300)")
 	thumbnail.IntVar(&opts.Filter, "filter", 2, "0=NearestNeighbor, 1=Box, 2=Linear, 3=MitchellNetravali, 4=CatmullRom, 6=Gaussian, 7=Lanczos")
 	thumbnail.StringVar(&opts.OutDir, "outdir", ".", "Output directory")
 	thumbnail.StringVar(&opts.OutFile, "outfile", "", "Output file")
@@ -236,7 +239,7 @@ func parseFlags() (cbconvert.Options, []string) {
 		fmt.Fprintf(os.Stderr, "Usage: %s <command> [<flags>] [file1 dir1 ... fileOrDirN]\n\n", filepath.Base(os.Args[0]))
 		fmt.Fprintf(os.Stderr, "\nCommands:\n")
 		fmt.Fprintf(os.Stderr, "\n  convert\n    \tConvert archive or document\n\n")
-		order := []string{"width", "height", "fit", "format", "archive", "zip-level", "quality", "effort", "lossless", "combine", "outfile", "filter", "no-cover", "no-rgb",
+		order := []string{"width", "height", "fit", "dpi", "format", "archive", "zip-level", "quality", "effort", "lossless", "combine", "outfile", "filter", "no-cover", "no-rgb",
 			"no-nonimage", "no-convert", "grayscale", "rotate", "brightness", "contrast", "suffix", "outdir", "size", "recursive", "quiet"}
 		for _, name := range order {
 			f := convert.Lookup(name)
@@ -244,14 +247,14 @@ func parseFlags() (cbconvert.Options, []string) {
 			fmt.Fprintf(os.Stderr, "%v (default %q)\n", f.Usage, f.DefValue)
 		}
 		fmt.Fprintf(os.Stderr, "\n  cover\n    \tExtract cover\n\n")
-		order = []string{"width", "height", "fit", "format", "quality", "effort", "lossless", "combine", "outfile", "filter", "outdir", "size", "recursive", "quiet"}
+		order = []string{"width", "height", "fit", "dpi", "format", "quality", "effort", "lossless", "filter", "outdir", "size", "recursive", "quiet"}
 		for _, name := range order {
 			f := cover.Lookup(name)
 			fmt.Fprintf(os.Stderr, "    --%s\n    \t", f.Name)
 			fmt.Fprintf(os.Stderr, "%v (default %q)\n", f.Usage, f.DefValue)
 		}
 		fmt.Fprintf(os.Stderr, "\n  thumbnail\n    \tExtract cover thumbnail (freedesktop spec.)\n\n")
-		order = []string{"width", "height", "fit", "filter", "outdir", "outfile", "size", "recursive", "quiet"}
+		order = []string{"width", "height", "fit", "dpi", "filter", "outdir", "outfile", "size", "recursive", "quiet"}
 		for _, name := range order {
 			f := thumbnail.Lookup(name)
 			fmt.Fprintf(os.Stderr, "    --%s\n    \t", f.Name)