PDFBox: draw millimeter paper - javafx

Question

I want to draw millimeter paper into a pdf, but when I measure the printed document I'm a bit off (drawn cm < 1 cm). I'm using the size of an A4 Paper (210 * 297) and the pageWidth and pageHeight to calculate the pixel per mm (used the average of both hoping this would work). I also tried different option when printing the document (with & without margin etc.), but this didn't work as well.
public class TestPrint extends Application {
protected static final float DINA4_IN_MM_WIDTH = 210;
protected static final float DINA4_IN_MM_HEIGHT = 297;
protected static final int LEFTSIDE = 35;
protected static final int TEXT_FONT_SIZE = 11;
protected static final int TOP_MARGIN = 60;
public static void main(String[] args) {
launch(args);
}
#Override
public void start(Stage primaryStage) {
File file = new File("test.pdf");
double windowWidth = 600;
double windowHeight = 1000;
float x = LEFTSIDE;
PDFont font = PDType1Font.TIMES_ROMAN;
PDPage page = new PDPage(PDRectangle.A4);
PDRectangle pageSize = page.getMediaBox();
PDDocument mainDocument = new PDDocument();
mainDocument.addPage(page);
float stringHeight = font.getFontDescriptor().getFontBoundingBox().getHeight() * TEXT_FONT_SIZE;
float y = pageSize.getHeight() - stringHeight / 1000f - TOP_MARGIN;
float pixelPerMM = (pageSize.getWidth() / DINA4_IN_MM_WIDTH + pageSize.getHeight() / DINA4_IN_MM_HEIGHT) / 2;
float displayW = 520;
float displayH = 300;
try {
PDPageContentStream contents = new PDPageContentStream(mainDocument, page, AppendMode.APPEND, true);
drawBackgroundRaster(contents, x, y, displayW, displayH, pixelPerMM);
contents.close();
mainDocument.save(file);
ImageView imgView = getImageViewFromDocument(mainDocument, windowHeight);
VBox vBox = new VBox(imgView);
Scene scene = new Scene(vBox, windowWidth, windowHeight);
primaryStage.setScene(scene);
primaryStage.show();
} catch (IOException e) {
e.printStackTrace();
}
}
// draw millimeter paper with dots, two boxes shall be 1cm
private void drawBackgroundRaster(PDPageContentStream contents, float x, float y, float displayW, float displayH,
float pixelPerMM) throws IOException {
// rasterColor = grey
Color rasterColor = new Color(175, 175, 175);
contents.setStrokingColor(rasterColor);
float dotSize = 0.5f;
// draw vertical lines
for (int i = 0; i <= displayW; i++) {
float xPos = x + i * pixelPerMM;
if (xPos > displayW + x) {
break;
}
contents.moveTo(xPos, y);
if (i % 5 == 0) {
contents.setLineDashPattern(new float[] {}, 0);
contents.lineTo(xPos, y - displayH);
}
contents.stroke();
}
// draw dots and horizontal lines
for (int i = 0; i <= displayH; i++) {
float yPos = y - i * pixelPerMM;
if (yPos < y - displayH) {
break;
}
contents.moveTo(x, yPos);
if (i % 5 == 0) {
contents.setLineDashPattern(new float[] {}, 0);
contents.lineTo(x + displayW, yPos);
} else {
contents.setLineDashPattern(new float[] { dotSize, pixelPerMM - dotSize }, dotSize / 2);
contents.lineTo(x + displayW, yPos);
}
contents.stroke();
}
contents.setLineDashPattern(new float[] {}, 0);
contents.moveTo(x, y);
contents.lineTo(x + displayW, y);
contents.lineTo(x + displayW, y - displayH);
contents.lineTo(x, y - displayH);
contents.lineTo(x, y);
contents.stroke();
}
private ImageView getImageViewFromDocument(PDDocument mainDocument, double windowHeight) throws IOException {
PDFRenderer pdfRenderer = new PDFRenderer(mainDocument);
BufferedImage bim = pdfRenderer.renderImageWithDPI(0, 150, ImageType.RGB);
Image image = SwingFXUtils.toFXImage(bim, null);
ImageView imageView = new ImageView(image);
double scaleFactor = windowHeight / imageView.getImage().getHeight();
double zoomFactor = scaleFactor * 2d * 2.55d / 3;
double width = imageView.getImage().getWidth() * zoomFactor;
double height = imageView.getImage().getHeight() * zoomFactor;
imageView.setFitWidth(width);
imageView.setFitHeight(height);
return imageView;
}
}