[webkit-dev] Handling Ignorable Text in a Renderer

David Hyatt hyatt at apple.com
Wed Aug 26 13:36:55 PDT 2009

If you have your own renderobject subclass you can override:

virtual bool isChildAllowed(RenderObject*, RenderStyle*) const  
{ return true; }

If you don't have your own subclass, then it's trickier.  You  
basically can suppress the creation of RenderTexts completely inside

bool Text::rendererIsNeeded(RenderStyle *style)

However, that function is extremely performance critical, so any code  
that gets added to that function would need to be examined very  

You might want to study some of what SVG did on the DOM side of things  
to suppress the creation of renderers.  I believe Eric Seidel did that  
work and could help you out.  I suspect there might be similarities.

(hyatt at apple.com)

On Aug 26, 2009, at 1:19 PM, Alex Milowski wrote:

> On Wed, Aug 26, 2009 at 12:06 PM, Alex Milowski<alex at milowski.org>  
> wrote:
>> In certain MathML constructs (e.g. mfenced) there are a number of  
>> child
>> elements that make up the construct and need to be rendered.  Any  
>> text
>> between those child elements should be ignored.  In fact, non- 
>> whitespace
>> text in the wrong place is most certainly incorrect but something
>> that can be recovered from.
>> I don't want to remove the text from the DOM nodes but I need to
>> keep the RenderText instances from being created or displayed.  What
>> is the correct way to do this?
>> I've been trying to handle this in the renderer but it seems like  
>> that
>> is really too late.  I though about changing the attach method to  
>> exclude
>> such ignorable text.
> Here's what works but it feels like a hack:
> 		RenderBlock* none = new (renderArena()) RenderBlock(document());
> 		RefPtr<RenderStyle> newStyle = RenderStyle::create();
> 		newStyle->inheritFrom(style());
> 		newStyle->setDisplay(INLINE_BLOCK);
> 		newStyle->setMaxWidth(Length(0,Fixed));
> 		newStyle->setMaxHeight(Length(0,Fixed));
> 		newStyle->setOverflowX(OHIDDEN);
> 		newStyle->setOverflowY(OHIDDEN);
> 		none->setStyle(newStyle.release());
> 		RenderBlock::addChild(none, beforeChild);
> 		none->addChild(child);
> I basically create an inline block with zero width and height and then
> set the overflow to hidden.
> -- 
> --Alex Milowski
> "The excellence of grammar as a guide is proportional to the paucity  
> of the
> inflexions, i.e. to the degree of analysis effected by the language
> considered."
> Bertrand Russell in a footnote of Principles of Mathematics
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