Form fill field rotation (#385)

* Refactor text field rotation

* Add rotation support for checkbox fields

* Add rotation support for combobox fields

* Add rotation support for text combobox fields

* Add documentation for the applyRotation of the AppearanceStyle

annotator/field_appearance.go

@@ -219,15 +219,15 @@ func genFieldTextAppearance(wa *model.PdfAnnotationWidget, ftxt *model.PdfFieldT
 		return nil, err
 	}
 	width, height := rect.Width(), rect.Height()
+	bboxWidth, bboxHeight := width, height
 
-	var rotation float64
+	mkDict, has := core.GetDict(wa.MK)
-	if mkDict, has := core.GetDict(wa.MK); has {
+	if has {
 		bsDict, _ := core.GetDict(wa.BS)
 		err := style.applyAppearanceCharacteristics(mkDict, bsDict, nil)
 		if err != nil {
 			return nil, err
 		}
-		rotation, _ = core.GetNumberAsFloat(mkDict.Get("R"))
 	}
 
 	// Get and process the default appearance string (DA) operands.
@@ -252,26 +252,10 @@ func genFieldTextAppearance(wa *model.PdfAnnotationWidget, ftxt *model.PdfFieldT
 	cc.Add_BMC("Tx")
 	cc.Add_q()
 
-	bboxWidth, bboxHeight := width, height
+	// Apply rotation if present.
-	if rotation != 0 {
+	// Update width and height, as the appearance is generated based on
-		// Calculate bounding box before rotation.
+	// the bounding of the annotation with no rotation.
-		revRotation := -rotation
+	width, height = style.applyRotation(mkDict, width, height, cc)
-		bbox := draw.Path{Points: []draw.Point{
-			draw.NewPoint(0, 0).Rotate(revRotation),
-			draw.NewPoint(width, 0).Rotate(revRotation),
-			draw.NewPoint(0, height).Rotate(revRotation),
-			draw.NewPoint(width, height).Rotate(revRotation),
-		}}.GetBoundingBox()
-
-		// Update width and height, as the appearance is generated based on
-		// the bounding of the annotation with no rotation.
-		width = bbox.Width
-		height = bbox.Height
-
-		// Apply rotation.
-		cc.RotateDeg(rotation)
-		cc.Translate(bbox.X, bbox.Y)
-	}
 
 	// Graphic state changes.
 	cc.Add_BT()
@@ -513,8 +497,10 @@ func genFieldTextCombAppearance(wa *model.PdfAnnotationWidget, ftxt *model.PdfFi
 		return nil, err
 	}
 	width, height := rect.Width(), rect.Height()
+	bboxWidth, bboxHeight := width, height
 
-	if mkDict, has := core.GetDict(wa.MK); has {
+	mkDict, has := core.GetDict(wa.MK)
+	if has {
 		bsDict, _ := core.GetDict(wa.BS)
 		err := style.applyAppearanceCharacteristics(mkDict, bsDict, nil)
 		if err != nil {
@@ -551,6 +537,11 @@ func genFieldTextCombAppearance(wa *model.PdfAnnotationWidget, ftxt *model.PdfFi
 	cc.Add_BMC("Tx")
 	cc.Add_q()
 
+	// Apply rotation if present.
+	// Update width and height, as the appearance is generated based on
+	// the bounding of the annotation with no rotation.
+	width, height = style.applyRotation(mkDict, width, height, cc)
+
 	// Graphic state changes.
 	cc.Add_BT()
 
@@ -680,7 +671,7 @@ func genFieldTextCombAppearance(wa *model.PdfAnnotationWidget, ftxt *model.PdfFi
 
 	xform := model.NewXObjectForm()
 	xform.Resources = resources
-	xform.BBox = core.MakeArrayFromFloats([]float64{0, 0, width, height})
+	xform.BBox = core.MakeArrayFromFloats([]float64{0, 0, bboxWidth, bboxHeight})
 	xform.SetContentStream(cc.Bytes(), defStreamEncoder())
 
 	apDict := core.MakeDict()
@@ -702,6 +693,7 @@ func genFieldCheckboxAppearance(wa *model.PdfAnnotationWidget, fbtn *model.PdfFi
 		return nil, err
 	}
 	width, height := rect.Width(), rect.Height()
+	bboxWidth, bboxHeight := width, height
 
 	common.Log.Debug("Checkbox, wa BS: %v", wa.BS)
 
@@ -710,7 +702,8 @@ func genFieldCheckboxAppearance(wa *model.PdfAnnotationWidget, fbtn *model.PdfFi
 		return nil, err
 	}
 
-	if mkDict, has := core.GetDict(wa.MK); has {
+	mkDict, has := core.GetDict(wa.MK)
+	if has {
 		bsDict, _ := core.GetDict(wa.BS)
 		err := style.applyAppearanceCharacteristics(mkDict, bsDict, zapfdb)
 		if err != nil {
@@ -732,6 +725,11 @@ func genFieldCheckboxAppearance(wa *model.PdfAnnotationWidget, fbtn *model.PdfFi
 			drawAlignmentReticle(cc, style2, width, height)
 		}
 
+		// Apply rotation if present.
+		// Update width and height, as the appearance is generated based on
+		// the bounding of the annotation with no rotation.
+		width, height = style.applyRotation(mkDict, width, height, cc)
+
 		fontsize := style.AutoFontSizeFraction * height
 
 		checkmetrics, ok := zapfdb.GetRuneMetrics(style.CheckmarkRune)
@@ -767,7 +765,7 @@ func genFieldCheckboxAppearance(wa *model.PdfAnnotationWidget, fbtn *model.PdfFi
 
 		xformOn.Resources = model.NewPdfPageResources()
 		xformOn.Resources.SetFontByName("ZaDb", zapfdb.ToPdfObject())
-		xformOn.BBox = core.MakeArrayFromFloats([]float64{0, 0, width, height})
+		xformOn.BBox = core.MakeArrayFromFloats([]float64{0, 0, bboxWidth, bboxHeight})
 		xformOn.SetContentStream(cc.Bytes(), defStreamEncoder())
 	}
 
@@ -777,7 +775,7 @@ func genFieldCheckboxAppearance(wa *model.PdfAnnotationWidget, fbtn *model.PdfFi
 		if style.BorderSize > 0 {
 			drawRect(cc, style, width, height)
 		}
-		xformOff.BBox = core.MakeArrayFromFloats([]float64{0, 0, width, height})
+		xformOff.BBox = core.MakeArrayFromFloats([]float64{0, 0, bboxWidth, bboxHeight})
 		xformOff.SetContentStream(cc.Bytes(), defStreamEncoder())
 	}
 
@@ -813,7 +811,8 @@ func genFieldComboboxAppearance(form *model.PdfAcroForm, wa *model.PdfAnnotation
 		return nil, err
 	}
 
-	if mkDict, has := core.GetDict(wa.MK); has {
+	mkDict, has := core.GetDict(wa.MK)
+	if has {
 		bsDict, _ := core.GetDict(wa.BS)
 		err := style.applyAppearanceCharacteristics(mkDict, bsDict, nil)
 		if err != nil {
@@ -839,7 +838,7 @@ func genFieldComboboxAppearance(form *model.PdfAcroForm, wa *model.PdfAnnotation
 		}
 
 		if len(optstr) > 0 {
-			xform, err := makeComboboxTextXObjForm(fch.PdfField, width, height, optstr, style, daOps, form.DR)
+			xform, err := makeComboboxTextXObjForm(fch.PdfField, width, height, optstr, style, daOps, form.DR, mkDict)
 			if err != nil {
 				return nil, err
 			}
@@ -857,8 +856,9 @@ func genFieldComboboxAppearance(form *model.PdfAcroForm, wa *model.PdfAnnotation
 // Make a text-based XObj Form.
 func makeComboboxTextXObjForm(field *model.PdfField, width, height float64,
 	text string, style AppearanceStyle, daOps *contentstream.ContentStreamOperations,
-	dr *model.PdfPageResources) (*model.XObjectForm, error) {
+	dr *model.PdfPageResources, mkDict *core.PdfObjectDictionary) (*model.XObjectForm, error) {
 	resources := model.NewPdfPageResources()
+	bboxWidth, bboxHeight := width, height
 
 	cc := contentstream.NewContentCreator()
 	if style.BorderSize > 0 {
@@ -875,6 +875,11 @@ func makeComboboxTextXObjForm(field *model.PdfField, width, height float64,
 	// Graphic state changes.
 	cc.Add_BT()
 
+	// Apply rotation if present.
+	// Update width and height, as the appearance is generated based on
+	// the bounding of the annotation with no rotation.
+	width, height = style.applyRotation(mkDict, width, height, cc)
+
 	// Process DA operands.
 	apFont, hasTf, err := style.processDA(field, daOps, dr, resources, cc)
 	if err != nil {
@@ -950,7 +955,7 @@ func makeComboboxTextXObjForm(field *model.PdfField, width, height float64,
 
 	xform := model.NewXObjectForm()
 	xform.Resources = resources
-	xform.BBox = core.MakeArrayFromFloats([]float64{0, 0, width, height})
+	xform.BBox = core.MakeArrayFromFloats([]float64{0, 0, bboxWidth, bboxHeight})
 	xform.SetContentStream(cc.Bytes(), defStreamEncoder())
 
 	return xform, nil
@@ -1067,6 +1072,40 @@ func (style *AppearanceStyle) applyAppearanceCharacteristics(mkDict *core.PdfObj
 	return nil
 }
 
+// applyRotation applies the rotation specified by the MK dictionary,
+// if present. The method returns the width and height of the annotation
+// rectangle with no rotation.
+func (style *AppearanceStyle) applyRotation(mkDict *core.PdfObjectDictionary,
+	width, height float64, cc *contentstream.ContentCreator) (float64, float64) {
+	if !style.AllowMK {
+		return width, height
+	}
+	if mkDict == nil {
+		return width, height
+	}
+
+	// Extract rotation from the MK dictionary.
+	rotation, _ := core.GetNumberAsFloat(mkDict.Get("R"))
+	if rotation == 0 {
+		return width, height
+	}
+
+	// Calculate bounding box before rotation.
+	revRotation := -rotation
+	bbox := draw.Path{Points: []draw.Point{
+		draw.NewPoint(0, 0).Rotate(revRotation),
+		draw.NewPoint(width, 0).Rotate(revRotation),
+		draw.NewPoint(0, height).Rotate(revRotation),
+		draw.NewPoint(width, height).Rotate(revRotation),
+	}}.GetBoundingBox()
+
+	// Apply rotation.
+	cc.RotateDeg(rotation)
+	cc.Translate(bbox.X, bbox.Y)
+
+	return bbox.Width, bbox.Height
+}
+
 // processDA adds the operands found in the field default appearance stream to
 // the provided content stream creator. It also provides a fallback font, based
 // on the configuration of the AppearanceStyle, if no valid font is specified