Tryanks/pdfsign
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Image visual appearance

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This commit is contained in:
Corentin Mors
2025-04-28 16:55:59 +02:00
parent c958b32269
commit ce8274cc9c
5 changed files with 220 additions and 18 deletions
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134
sign/appearance.go
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@@ -3,11 +3,18 @@ package sign
import (
"bytes"
"fmt"
"image"
_ "image/jpeg" // register JPEG format
)
func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
text := context.SignData.Signature.Info.Name
if len(context.SignData.Signature.Info.Image) > 0 {
return context.createImageAppearance(rect)
}
return context.createTextAppearance(rect)
}
func (context *SignContext) createTextAppearance(rect [4]float64) ([]byte, error) {
rectWidth := rect[2] - rect[0]
rectHeight := rect[3] - rect[1]
@@ -15,23 +22,36 @@ func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
return nil, fmt.Errorf("invalid rectangle dimensions: width %.2f and height %.2f must be greater than 0", rectWidth, rectHeight)
}
var appearance_stream_buffer bytes.Buffer
text := context.SignData.Signature.Info.Name
// Calculate font size
fontSize := rectHeight * 0.8 // Initial font size
fontSize := rectHeight * 0.8 // Use most of the height for the font
textWidth := float64(len(text)) * fontSize * 0.5 // Approximate text width
if textWidth > rectWidth {
fontSize = rectWidth / (float64(len(text)) * 0.5) // Adjust font size to fit text within rect width
}
var appearance_stream_buffer bytes.Buffer
appearance_stream_buffer.WriteString("q\n") // Save graphics state
appearance_stream_buffer.WriteString("BT\n") // Begin text
appearance_stream_buffer.WriteString(fmt.Sprintf("/F1 %.2f Tf\n", fontSize)) // Font and size
appearance_stream_buffer.WriteString(fmt.Sprintf("0 %.2f Td\n", rectHeight-fontSize)) // Position in unit square
appearance_stream_buffer.WriteString("0.2 0.2 0.6 rg\n") // Set font color to ballpoint-like color (RGB)
appearance_stream_buffer.WriteString(fmt.Sprintf("%s Tj\n", pdfString(text))) // Show text
appearance_stream_buffer.WriteString("ET\n") // End text
appearance_stream_buffer.WriteString("Q\n") // Restore graphics state
appearance_stream_buffer.WriteString("q\n") // Save graphics state
appearance_stream_buffer.WriteString("BT\n") // Begin text
appearance_stream_buffer.WriteString(fmt.Sprintf("/F1 %.2f Tf\n", fontSize)) // Font and size
// Center text horizontally and vertically
textWidth = float64(len(text)) * fontSize * 0.5
textX := (rectWidth - textWidth) / 2
if textX < 0 {
textX = 0
}
textY := (rectHeight-fontSize)/2 + fontSize/3 // Approximate vertical centering
appearance_stream_buffer.WriteString(fmt.Sprintf("%.2f %.2f Td\n", textX, textY)) // Position text
appearance_stream_buffer.WriteString("0.2 0.2 0.6 rg\n") // Set font color to ballpoint-like color (RGB)
appearance_stream_buffer.WriteString(fmt.Sprintf("%s Tj\n", pdfString(text))) // Show text
appearance_stream_buffer.WriteString("ET\n") // End text
appearance_stream_buffer.WriteString("Q\n") // Restore graphics state
// Create the appearance XObject
var appearance_buffer bytes.Buffer
appearance_buffer.WriteString("<<\n")
appearance_buffer.WriteString(" /Type /XObject\n")
@@ -39,7 +59,7 @@ func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
appearance_buffer.WriteString(fmt.Sprintf(" /BBox [0 0 %f %f]\n", rectWidth, rectHeight))
appearance_buffer.WriteString(" /Matrix [1 0 0 1 0 0]\n") // No scaling or translation
// Resources dictionary
// Resources dictionary with font
appearance_buffer.WriteString(" /Resources <<\n")
appearance_buffer.WriteString(" /Font <<\n")
appearance_buffer.WriteString(" /F1 <<\n")
@@ -60,3 +80,93 @@ func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
return appearance_buffer.Bytes(), nil
}
func (context *SignContext) createImageAppearance(rect [4]float64) ([]byte, error) {
rectWidth := rect[2] - rect[0]
rectHeight := rect[3] - rect[1]
if rectWidth < 1 || rectHeight < 1 {
return nil, fmt.Errorf("invalid rectangle dimensions: width %.2f and height %.2f must be greater than 0", rectWidth, rectHeight)
}
// Create and add the image XObject
imageStream, err := context.createImageXObject()
if err != nil {
return nil, fmt.Errorf("failed to create image XObject: %w", err)
}
imageObjectId, err := context.addObject(imageStream)
if err != nil {
return nil, fmt.Errorf("failed to add image object: %w", err)
}
var appearance_stream_buffer bytes.Buffer
// We save state twice on purpose due to the cm operation
appearance_stream_buffer.WriteString("q\n") // Save graphics state
appearance_stream_buffer.WriteString("q\n") // Save before image transformation
appearance_stream_buffer.WriteString(fmt.Sprintf("%.2f 0 0 %.2f 0 0 cm\n", rectWidth, rectHeight))
appearance_stream_buffer.WriteString("/Im1 Do\n")
appearance_stream_buffer.WriteString("Q\n") // Restore after transformation
appearance_stream_buffer.WriteString("Q\n") // Restore graphics state
// Create the appearance XObject
var appearance_buffer bytes.Buffer
appearance_buffer.WriteString("<<\n")
appearance_buffer.WriteString(" /Type /XObject\n")
appearance_buffer.WriteString(" /Subtype /Form\n")
appearance_buffer.WriteString(fmt.Sprintf(" /BBox [0 0 %f %f]\n", rectWidth, rectHeight))
// Resources dictionary with XObject
appearance_buffer.WriteString(" /Resources <<\n")
appearance_buffer.WriteString(" /XObject <<\n")
appearance_buffer.WriteString(fmt.Sprintf(" /Im1 %d 0 R\n", imageObjectId))
appearance_buffer.WriteString(" >>\n")
appearance_buffer.WriteString(" >>\n")
appearance_buffer.WriteString(" /FormType 1\n")
appearance_buffer.WriteString(fmt.Sprintf(" /Length %d\n", appearance_stream_buffer.Len()))
appearance_buffer.WriteString(">>\n")
appearance_buffer.WriteString("stream\n")
appearance_buffer.Write(appearance_stream_buffer.Bytes())
appearance_buffer.WriteString("endstream\n")
return appearance_buffer.Bytes(), nil
}
func (context *SignContext) createImageXObject() ([]byte, error) {
imageData := context.SignData.Signature.Info.Image
// Read image configuration to get original dimensions
img, _, err := image.DecodeConfig(bytes.NewReader(imageData))
if err != nil {
return nil, fmt.Errorf("failed to decode image configuration: %w", err)
}
// Use original image dimensions
width := float64(img.Width)
height := float64(img.Height)
// Create basic PDF Image XObject
var imageObject bytes.Buffer
imageObject.WriteString("<<\n")
imageObject.WriteString(" /Type /XObject\n")
imageObject.WriteString(" /Subtype /Image\n")
imageObject.WriteString(fmt.Sprintf(" /Width %.0f\n", width))
imageObject.WriteString(fmt.Sprintf(" /Height %.0f\n", height))
imageObject.WriteString(" /ColorSpace /DeviceRGB\n")
imageObject.WriteString(" /BitsPerComponent 8\n")
imageObject.WriteString(" /Filter /DCTDecode\n") // JPEG compression
imageObject.WriteString(fmt.Sprintf(" /Length %d\n", len(imageData)))
imageObject.WriteString(">>\n")
imageObject.WriteString("stream\n")
imageObject.Write(imageData)
imageObject.WriteString("\nendstream\n")
return imageObject.Bytes(), nil
}