Accessible math showing as white text against the "DRAFT" watermark

[ronaldtse]

Example below:

Is it possible to not show the accessible math as white text at all (e.g. 100% transparency of text)?

[Intelligent2013]

In XSL-FO there isn't property to set text transparency. I'll investigate how to tweak it. At first glance there are two options (don't sure where they can be applited yet):

• move text behind background image with watermark (change z-order)
• set 'Text rendering mode' to 3 Tr (9.3.6 in PDF Spec):
  

[ronaldtse]

Looks like both are good options and probably should do both. And we should extend the previous blog post with this new technique too.

[Intelligent2013]

mn2pdf updated for 1st option (metanorma/mn2pdf@6b66616)

move text behind background image with watermark (change z-order)

Text is searchable - checked:

[Intelligent2013]

Regarding 2nd option, the the FOP class fop-core\src\main\java\org\apache\fop\pdf\PDFTextUtil.java there are constants:

/** PDF text rendering mode: Fill text */
    public static final int TR_FILL = 0;
    /** PDF text rendering mode: Stroke text */
    public static final int TR_STROKE = 1;
    /** PDF text rendering mode: Fill, then stroke text */
    public static final int TR_FILL_STROKE = 2;
    /** PDF text rendering mode: Neither fill nor stroke text (invisible) */
    public static final int TR_INVISIBLE = 3;
    /** PDF text rendering mode: Fill text and add to path for clipping */
    public static final int TR_FILL_CLIP = 4;
    /** PDF text rendering mode: Stroke text and add to path for clipping */
    public static final int TR_STROKE_CLIP = 5;
    /** PDF text rendering mode: Fill, then stroke text and add to path for clipping */
    public static final int TR_FILL_STROKE_CLIP = 6;
    /** PDF text rendering mode: Add text to path for clipping */
    public static final int TR_CLIP = 7;

and the method setTextRenderingMode:

/**
     * Sets the text rendering mode.
     * @param mode the rendering mode (value 0 to 7, see PDF Spec, constants: TR_*)
     */
    public void setTextRenderingMode(int mode) {
        if (mode < 0 || mode > 7) {
            throw new IllegalArgumentException(
                    "Illegal value for text rendering mode. Expected: 0-7");
        }
        if (mode != this.textRenderingMode) {
            writeTJ();
            this.textRenderingMode = mode;
            write(this.textRenderingMode + " Tr\n");
        }
    }

It seems the class org\apache\fop\render\pdf\PDFPainter.java should be modified to call setTextRenderingMode(int mode).

[Intelligent2013]

mn2pdf updated for 2nd option.

[Intelligent2013]

Issue found with the text selection.
Before update (both options) we can select the text before formula, formula and text after formula:

After update - the formula isn't selected:

but we can select the formula only:

Looks like the text selection feature depends on the element depth (z-order) or the rendering order.
May be we need to remove 1st option. Will check it.

[Intelligent2013]

Now the hidden text placed at start of page, therefore we need to remove 1st option.

PDF Before update:

Currently generated PDF:

[Intelligent2013]

1st option removed.

[Intelligent2013]

@ronaldtse issue fixed in https://github.com/metanorma/mn2pdf/releases/tag/v1.49

Blog post updated a bit in PR metanorma/metanorma.org#640