202 lines
7.0 KiB
Go
202 lines
7.0 KiB
Go
package sign
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import (
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"bytes"
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"fmt"
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"image"
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_ "image/jpeg" // register JPEG format
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)
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func (context *SignContext) createAppearance(rect [4]float64) ([]byte, error) {
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if len(context.SignData.Appearance.Image) > 0 {
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return context.createImageAppearance(rect)
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}
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return context.createTextAppearance(rect)
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}
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// Helper functions for PDF resource components
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// writeAppearanceHeader writes the header for the appearance stream.
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//
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// Should be closed by writeFormTypeAndLength.
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func writeAppearanceHeader(buffer *bytes.Buffer, rectWidth, rectHeight float64) {
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buffer.WriteString("<<\n")
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buffer.WriteString(" /Type /XObject\n")
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buffer.WriteString(" /Subtype /Form\n")
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buffer.WriteString(fmt.Sprintf(" /BBox [0 0 %f %f]\n", rectWidth, rectHeight))
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buffer.WriteString(" /Matrix [1 0 0 1 0 0]\n") // No scaling or translation
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}
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func createFontResource(buffer *bytes.Buffer) {
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buffer.WriteString(" /Font <<\n")
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buffer.WriteString(" /F1 <<\n")
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buffer.WriteString(" /Type /Font\n")
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buffer.WriteString(" /Subtype /Type1\n")
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buffer.WriteString(" /BaseFont /Times-Roman\n")
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buffer.WriteString(" >>\n")
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buffer.WriteString(" >>\n")
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}
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func createImageResource(buffer *bytes.Buffer, imageObjectId uint32) {
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buffer.WriteString(" /XObject <<\n")
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buffer.WriteString(fmt.Sprintf(" /Im1 %d 0 R\n", imageObjectId))
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buffer.WriteString(" >>\n")
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}
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func writeFormTypeAndLength(buffer *bytes.Buffer, streamLength int) {
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buffer.WriteString(" /FormType 1\n")
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buffer.WriteString(fmt.Sprintf(" /Length %d\n", streamLength))
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buffer.WriteString(">>\n")
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}
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func writeBufferStream(buffer *bytes.Buffer, stream []byte) {
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buffer.WriteString("stream\n")
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buffer.Write(stream)
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buffer.WriteString("endstream\n")
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}
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func (context *SignContext) createImageXObject() ([]byte, error) {
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imageData := context.SignData.Appearance.Image
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// Read image configuration to get original dimensions
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img, _, err := image.DecodeConfig(bytes.NewReader(imageData))
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if err != nil {
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return nil, fmt.Errorf("failed to decode image configuration: %w", err)
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}
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// Use original image dimensions
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width := float64(img.Width)
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height := float64(img.Height)
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// Create basic PDF Image XObject
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var imageObject bytes.Buffer
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imageObject.WriteString("<<\n")
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imageObject.WriteString(" /Type /XObject\n")
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imageObject.WriteString(" /Subtype /Image\n")
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imageObject.WriteString(fmt.Sprintf(" /Width %.0f\n", width))
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imageObject.WriteString(fmt.Sprintf(" /Height %.0f\n", height))
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imageObject.WriteString(" /ColorSpace /DeviceRGB\n")
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imageObject.WriteString(" /BitsPerComponent 8\n")
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imageObject.WriteString(" /Filter /DCTDecode\n")
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imageObject.WriteString(fmt.Sprintf(" /Length %d\n", len(imageData)))
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imageObject.WriteString(">>\n")
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imageObject.WriteString("stream\n")
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imageObject.Write(imageData)
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imageObject.WriteString("\nendstream\n")
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return imageObject.Bytes(), nil
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}
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func computeTextSizeAndPosition(text string, rectWidth, rectHeight float64) (float64, float64, float64) {
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// Calculate font size
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fontSize := rectHeight * 0.8 // Use most of the height for the font
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textWidth := float64(len(text)) * fontSize * 0.5 // Approximate text width
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if textWidth > rectWidth {
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fontSize = rectWidth / (float64(len(text)) * 0.5) // Adjust font size to fit text within rect width
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}
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// Center text horizontally and vertically
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textWidth = float64(len(text)) * fontSize * 0.5
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textX := (rectWidth - textWidth) / 2
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if textX < 0 {
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textX = 0
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}
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textY := (rectHeight-fontSize)/2 + fontSize/3 // Approximate vertical centering
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return fontSize, textX, textY
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}
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func drawText(buffer *bytes.Buffer, text string, fontSize float64, x, y float64) {
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buffer.WriteString("q\n") // Save graphics state
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buffer.WriteString("BT\n") // Begin text
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buffer.WriteString(fmt.Sprintf("/F1 %.2f Tf\n", fontSize)) // Set font and size
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buffer.WriteString(fmt.Sprintf("%.2f %.2f Td\n", x, y)) // Set text position
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buffer.WriteString("0.2 0.2 0.6 rg\n") // Set font color to ballpoint-like color (RGB)
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buffer.WriteString(fmt.Sprintf("%s Tj\n", pdfString(text))) // Show text
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buffer.WriteString("ET\n") // End text
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buffer.WriteString("Q\n") // Restore graphics state
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}
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func drawImage(buffer *bytes.Buffer, rectWidth, rectHeight float64) {
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// We save state twice on purpose due to the cm operation
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buffer.WriteString("q\n") // Save graphics state
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buffer.WriteString("q\n") // Save before image transformation
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buffer.WriteString(fmt.Sprintf("%.2f 0 0 %.2f 0 0 cm\n", rectWidth, rectHeight))
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buffer.WriteString("/Im1 Do\n") // Draw image
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buffer.WriteString("Q\n") // Restore after transformation
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buffer.WriteString("Q\n") // Restore graphics state
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}
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func (context *SignContext) createTextAppearance(rect [4]float64) ([]byte, error) {
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rectWidth := rect[2] - rect[0]
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rectHeight := rect[3] - rect[1]
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if rectWidth < 1 || rectHeight < 1 {
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return nil, fmt.Errorf("invalid rectangle dimensions: width %.2f and height %.2f must be greater than 0", rectWidth, rectHeight)
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}
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text := context.SignData.Signature.Info.Name
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fontSize, textX, textY := computeTextSizeAndPosition(text, rectWidth, rectHeight)
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var appearance_stream_buffer bytes.Buffer
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drawText(&appearance_stream_buffer, text, fontSize, textX, textY)
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// Create the appearance XObject
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var appearance_buffer bytes.Buffer
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writeAppearanceHeader(&appearance_buffer, rectWidth, rectHeight)
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// Resources dictionary with font
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appearance_buffer.WriteString(" /Resources <<\n")
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createFontResource(&appearance_buffer)
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appearance_buffer.WriteString(" >>\n")
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writeFormTypeAndLength(&appearance_buffer, appearance_stream_buffer.Len())
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writeBufferStream(&appearance_buffer, appearance_stream_buffer.Bytes())
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return appearance_buffer.Bytes(), nil
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}
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func (context *SignContext) createImageAppearance(rect [4]float64) ([]byte, error) {
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rectWidth := rect[2] - rect[0]
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rectHeight := rect[3] - rect[1]
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if rectWidth < 1 || rectHeight < 1 {
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return nil, fmt.Errorf("invalid rectangle dimensions: width %.2f and height %.2f must be greater than 0", rectWidth, rectHeight)
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}
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// Create and add the image XObject
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imageStream, err := context.createImageXObject()
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if err != nil {
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return nil, fmt.Errorf("failed to create image XObject: %w", err)
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}
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imageObjectId, err := context.addObject(imageStream)
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if err != nil {
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return nil, fmt.Errorf("failed to add image object: %w", err)
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}
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var appearance_stream_buffer bytes.Buffer
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drawImage(&appearance_stream_buffer, rectWidth, rectHeight)
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// Create the appearance XObject
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var appearance_buffer bytes.Buffer
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writeAppearanceHeader(&appearance_buffer, rectWidth, rectHeight)
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// Resources dictionary with XObject
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appearance_buffer.WriteString(" /Resources <<\n")
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createImageResource(&appearance_buffer, imageObjectId)
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appearance_buffer.WriteString(" >>\n")
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writeFormTypeAndLength(&appearance_buffer, appearance_stream_buffer.Len())
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writeBufferStream(&appearance_buffer, appearance_stream_buffer.Bytes())
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return appearance_buffer.Bytes(), nil
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}
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