Tryanks/pdfsign
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Implement image watermark

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This commit is contained in:
Corentin Mors
2025-05-01 11:06:11 +02:00
parent a3b23161c4
commit abd05a5aaa
4 changed files with 86 additions and 53 deletions
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87
sign/appearance.go
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@@ -7,13 +7,6 @@ import (
_ "image/jpeg" // register JPEG format
)
func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
if len(context.SignData.Appearance.Image) > 0 {
return context.createImageAppearance(rect)
}
return context.createTextAppearance(rect)
}
// Helper functions for PDF resource components
// writeAppearanceHeader writes the header for the appearance stream.
@@ -49,7 +42,7 @@ func writeFormTypeAndLength(buffer *bytes.Buffer, streamLength int) {
buffer.WriteString(">>\n")
}
func writeBufferStream(buffer *bytes.Buffer, stream []byte) {
func writeAppearanceStreamBuffer(buffer *bytes.Buffer, stream []byte) {
buffer.WriteString("stream\n")
buffer.Write(stream)
buffer.WriteString("endstream\n")
@@ -129,7 +122,7 @@ func drawImage(buffer *bytes.Buffer, rectWidth, rectHeight float64) {
buffer.WriteString("Q\n") // Restore graphics state
}
func (context *SignContext) createTextAppearance(rect [4]float64) ([]byte, error) {
func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
rectWidth := rect[2] - rect[0]
rectHeight := rect[3] - rect[1]
@@ -137,13 +130,8 @@ func (context *SignContext) createTextAppearance(rect [4]float64) ([]byte, error
return nil, fmt.Errorf("invalid rectangle dimensions: width %.2f and height %.2f must be greater than 0", rectWidth, rectHeight)
}
text := context.SignData.Signature.Info.Name
fontSize, textX, textY := computeTextSizeAndPosition(text, rectWidth, rectHeight)
var appearance_stream_buffer bytes.Buffer
drawText(&appearance_stream_buffer, text, fontSize, textX, textY)
hasImage := len(context.SignData.Appearance.Image) > 0
shouldDisplayText := context.SignData.Appearance.ImageAsWatermark || !hasImage
// Create the appearance XObject
var appearance_buffer bytes.Buffer
@@ -151,51 +139,44 @@ func (context *SignContext) createTextAppearance(rect [4]float64) ([]byte, error
// Resources dictionary with font
appearance_buffer.WriteString(" /Resources <<\n")
createFontResource(&appearance_buffer)
if hasImage {
// 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)
}
createImageResource(&appearance_buffer, imageObjectId)
}
if shouldDisplayText {
createFontResource(&appearance_buffer)
}
appearance_buffer.WriteString(" >>\n")
writeFormTypeAndLength(&appearance_buffer, appearance_stream_buffer.Len())
writeBufferStream(&appearance_buffer, appearance_stream_buffer.Bytes())
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)
}
// Create the appearance stream
var appearance_stream_buffer bytes.Buffer
drawImage(&appearance_stream_buffer, rectWidth, rectHeight)
if hasImage {
drawImage(&appearance_stream_buffer, rectWidth, rectHeight)
}
// Create the appearance XObject
var appearance_buffer bytes.Buffer
writeAppearanceHeader(&appearance_buffer, rectWidth, rectHeight)
// Resources dictionary with XObject
appearance_buffer.WriteString(" /Resources <<\n")
createImageResource(&appearance_buffer, imageObjectId)
appearance_buffer.WriteString(" >>\n")
if shouldDisplayText {
text := context.SignData.Signature.Info.Name
fontSize, textX, textY := computeTextSizeAndPosition(text, rectWidth, rectHeight)
drawText(&appearance_stream_buffer, text, fontSize, textX, textY)
}
writeFormTypeAndLength(&appearance_buffer, appearance_stream_buffer.Len())
writeBufferStream(&appearance_buffer, appearance_stream_buffer.Bytes())
writeAppearanceStreamBuffer(&appearance_buffer, appearance_stream_buffer.Bytes())
return appearance_buffer.Bytes(), nil
}