Proper way to implement custom Css attribute with Itext and html2Pdf - itext

Question

I'm using Itext 7 and their html2Pdf lib.
Is there a way to implement for example cmyk colors.
.wootWorkingCMYK-color{
color: cmyk( 1 , 0.69 , 0.08 , 0.54);
}
I know the itext core part pretty good, looking for away to use the html2Pdf side. I'm aware of the CssApplierFactory but this seems to be to far up the chain.

Answer 1

Well, of course there is a way of processing custom CSS properties like cmyk colors, but unfortunately the code would be quite bulky and you will need to write quite some code for different cases. I will show how to apply custom color for font, but e.g. for backgrounds, borders or other cases you will need to write separate code in a similar way. Reason behind it is that iText layout structure, although designed with HTML/CSS in mind, is not 100% similar and has some differences you have to code around.
Having that said, if you can fork, build and use your custom version from sources, this is the way I would advice to go. Although it has drawbacks like having to rebase to get updates, the solution would be simpler and more generic. To do that, search for usages of CssUtils.parseRgbaColor in pdfHTML module, and you will find that it is used in BackgroundApplierUtil, BorderStyleApplierUtil, FontStyleApplierUtil, OutlineApplierUtil. There you will find code like
if (!CssConstants.TRANSPARENT.equals(cssColorPropValue)) {
float[] rgbaColor = CssUtils.parseRgbaColor(cssColorPropValue);
Color color = new DeviceRgb(rgbaColor[0], rgbaColor[1], rgbaColor[2]);
float opacity = rgbaColor[3];
transparentColor = new TransparentColor(color, opacity);
} else {
transparentColor = new TransparentColor(ColorConstants.BLACK, 0f);
}
Which I belive you can tweak to process cmyk as well, knowing that you know core part pretty well.
Now, the solution without custom pdfHTML version is to indeed start with implementing ICssApplierFactory, or subclassing default implementation DefaultCssApplierFactory. We are mostly interested in customizing implementation of SpanTagCssApplier and BlockCssApplier, but you can consult with DefaultTagCssApplierMapping to get the full list of appliers and cases they are used in, so that you can decide which of them you want to process in your code.
I will show you how to add support for custom color space for font color in the two main applier classes I mentioned and you can work from there.
private static class CustomCssApplierFactory implements ICssApplierFactory {
private static final ICssApplierFactory DEFAULT_FACTORY = new DefaultCssApplierFactory();
#Override
public ICssApplier getCssApplier(IElementNode tag) {
ICssApplier defaultApplier = DEFAULT_FACTORY.getCssApplier(tag);
if (defaultApplier instanceof SpanTagCssApplier) {
return new CustomSpanTagCssApplier();
} else if (defaultApplier instanceof BlockCssApplier) {
return new CustomBlockCssApplier();
} else {
return defaultApplier;
}
}
}
private static class CustomSpanTagCssApplier extends SpanTagCssApplier {
#Override
protected void applyChildElementStyles(IPropertyContainer element, Map<String, String> css, ProcessorContext context, IStylesContainer stylesContainer) {
super.applyChildElementStyles(element, css, context, stylesContainer);
String color = css.get("color2");
if (color != null) {
color = color.trim();
if (color.startsWith("cmyk")) {
element.setProperty(Property.FONT_COLOR, new TransparentColor(parseCmykColor(color)));
}
}
}
}
private static class CustomBlockCssApplier extends BlockCssApplier {
#Override
public void apply(ProcessorContext context, IStylesContainer stylesContainer, ITagWorker tagWorker) {
super.apply(context, stylesContainer, tagWorker);
IPropertyContainer container = tagWorker.getElementResult();
if (container != null) {
String color = stylesContainer.getStyles().get("color2");
if (color != null) {
color = color.trim();
if (color.startsWith("cmyk")) {
container.setProperty(Property.FONT_COLOR, new TransparentColor(parseCmykColor(color)));
}
}
}
}
}
// You might want a safer implementation with better handling of corner cases
private static DeviceCmyk parseCmykColor(String color) {
final String delim = "cmyk(), \t\r\n\f";
StringTokenizer tok = new StringTokenizer(color, delim);
float[] res = new float[]{0, 0, 0, 0};
for (int k = 0; k < 3; ++k) {
if (tok.hasMoreTokens()) {
res[k] = Float.parseFloat(tok.nextToken());
}
}
return new DeviceCmyk(res[0], res[1], res[2], res[3]);
}
Having that custom code, you should configure the ConverterProperties accordingly and pass it to HtmlConverter:
ConverterProperties properties = new ConverterProperties();
properties.setCssApplierFactory(new CustomCssApplierFactory());
HtmlConverter.convertToPdf(..., properties);
You might have noticed that I used color2 instead of color, and this is for a reason. pdfHTML has a mechanism of CSS property validation (as browsers do as well), to discard invalid CSS properties when calculating effective properties for an element. Unfortunately, there is no mechanism of customizing this validation logic currently and of course it treats cmyk colors as invalid declarations at the moment. Thus, if you really want to have custom color property, you will have to preprocess your HTML and replace declarations like color: cmyk... to color2: cmyk.. or whatever the property name you might want to use.
As I mentioned at the start of the answer, my recommendation is to build your own custom version :)