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Two pass rendering

So, there was a question on the cdk-devel mailing list about bounding boxes, reactions, and text. An unfortunate consequence of the new design is that the renderer will not calculate bounding boxes that can fully contain the text. Concretely, this is what it would look like (not made in JCP!)


The blue box is the bounds that would be created, which is minimal with respect to the atom centers. The black box is the bounds that should be created, if we respected the text size. The problem is, the size of text is not known until the point it is drawn. Or, more precisely, until we have some sort of GraphicsContext to ask about the width in a particular font.

So, a two-pass system was suggested. When this was mentioned before, I was dismissive - perhaps even rude. Sorry about that Egon, Sam. I still think it is better avoided; in the case of transparency, I don't know why alpha values can't be used for fill colours. I understand there was some SWT problems..?

Anyway, here is a sketch of a possible two-pass system, that would allow some of these adjustments to be made:



That's unreadably small in thumbnail - click for bigger, as usual. The basic idea would be to have one element tree with model-space values, and one with screen space values. I've made the distinction between double and integer, but Java2D will draw with doubles, so that is not important.
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Comments

Egon Willighagen said…
Rude? You mean with your comment in that bug report? Subset: "Bugs are features which are broken, not features that work correctly, but in a way that is not desirable."

I fully agree with that statement!

Can you please repeat the rudeness, so that I understand what to be upset about? ;)
26 June 2009 at 12:03
gilleain said…
Well, Sam was helpfully making a bug report, and I was complaining about it, that's all.

Also, I dismissed a two-pass sytem without discussion, so that's what you can get annoyed about, if you like :)

In general with the rendering, I focus too much on speed at the expense of flexibility. I guess that small molecules need multiple precise representations more than they need ultra-fast drawing.
26 June 2009 at 12:23
Egon Willighagen said…
I was not offended. Indeed, there are plenty of reasons to dislike a two-pass system, and Arvid and I have been discussing it on several occasions. We, at least, have not come up with a different approach to getting things like this right.

At this moment, I am not sure what the bottleneck of drawing speed is... maybe Arvid and I can find some time next week to run YourKit (tm) against jchempaint-primary...
26 June 2009 at 16:38
gilleain said…
Well, whatever is done it has to achieve something like the following:

1) given a chem-model, generate the intermediate representation.
2) run through the element tree, either making a new scaled tree (as in the diagram) or calculating some properties, like a bounding box.
3) draw the tree, possibly after changing the scale.

in concrete terms, if a correct bounding box is to be made, the width on screen needs to be calculated, then the scale adjusted to compensate.

The double-tree approach is clean, but memory inefficient. Just calculating some properties (eg width, height) would be better, but less extensible.
26 June 2009 at 17:42
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