[US-234] Update form example to add a submit button

forms/pdf_form_add.go

@@ -14,6 +14,8 @@ import (
 
 	"github.com/unidoc/unipdf/v3/annotator"
 	"github.com/unidoc/unipdf/v3/common/license"
+	"github.com/unidoc/unipdf/v3/contentstream"
+	"github.com/unidoc/unipdf/v3/core"
 	"github.com/unidoc/unipdf/v3/model"
 )
 
@@ -161,5 +163,86 @@ func createForm(page *model.PdfPage) *model.PdfAcroForm {
 		page.AddAnnotation(comboboxf.Annotations[0].PdfAnnotation)
 	}
 
+	addSubmitButton(page, form)
+
 	return form
 }
+
+func addSubmitButton(page *model.PdfPage, form *model.PdfAcroForm) error {
+	submitUrl := "https://url-to-backend"
+	btnX := 400.0
+	btnY := 400.0
+	btnW := 50.0
+	btnH := 20.0
+
+	// Construct a new pdf field for the submit button.
+	field := model.NewPdfField()
+	btnField := &model.PdfFieldButton{}
+	field.SetContext(btnField)
+	btnField.PdfField = field
+
+	btnField.T = core.MakeString("btnSubmit")
+	btnField.SetType(model.ButtonTypePush)
+
+	btnField.V = core.MakeName("Off")
+	btnField.TU = core.MakeString("submit")
+
+	// Define an Action that will be executed when the button is clicked.
+	submitAction := model.NewPdfActionSubmitForm()
+	submitAction.Flags = core.MakeInteger(5) // This will submit all fields value using HTTP Form format.
+	submitAction.F = model.NewPdfFilespec()
+	submitAction.F.F = core.MakeString(submitUrl)
+	submitAction.F.FS = core.MakeName("URL")
+
+	widgetText := core.MakeDict()
+	widgetText.Set(*core.MakeName("CA"), core.MakeString("Submit"))
+
+	fontData, err := model.NewStandard14Font("Helvetica")
+	if err != nil {
+		return err
+	}
+	fontName := core.MakeName("Helv")
+
+	// Construct button.
+	cc := contentstream.NewContentCreator()
+	cc.Add_q()
+	cc.Add_g(0.7)
+	cc.Add_re(0, 0, btnW, btnH)
+	cc.Add_f()
+	cc.Add_Q()
+	cc.Add_q()
+	cc.Add_BT()
+	cc.Add_Tf(*fontName, 10)
+	cc.Add_g(0)
+	cc.Add_Td(5, 5)
+	cc.Add_Tj(*core.MakeString("Submit"))
+	cc.Add_ET()
+	cc.Add_Q()
+
+	xform := model.NewXObjectForm()
+	xform.SetContentStream(cc.Bytes(), core.NewRawEncoder())
+	xform.BBox = core.MakeArrayFromFloats([]float64{0, 0, btnW, btnH})
+	xform.Resources = model.NewPdfPageResources()
+	xform.Resources.SetFontByName(*fontName, fontData.ToPdfObject())
+
+	appearance := core.MakeDict()
+	appearance.Set("N", xform.ToPdfObject())
+
+	// Construct a widget annotation.
+	btnWidget := model.NewPdfAnnotationWidget()
+	btnWidget.Rect = core.MakeArrayFromFloats([]float64{btnX, btnY, btnX + btnW, btnY + btnH})
+	btnWidget.P = page.ToPdfObject()
+	btnWidget.F = core.MakeInteger(4)
+	btnWidget.Parent = btnField.ToPdfObject()
+	btnWidget.A = submitAction.ToPdfObject()
+	btnWidget.MK = widgetText
+	btnWidget.AP = appearance
+
+	btnField.Annotations = append(btnField.Annotations, btnWidget)
+
+	// Add widget to existing form.
+	*form.Fields = append(*form.Fields, btnField.PdfField)
+	page.AddAnnotation(btnField.Annotations[0].PdfAnnotation)
+
+	return nil
+}