[whatwg] Basic technical graphing features (canvas)
simonp at opera.com
Sun Feb 3 16:54:50 PST 2008
* Missing dashed lines, Hershey/vector fonts, even-odd polygon fill
rules, and points.
* http://home.comcast.net/~urbanjost/canvas/vogle4.html hence uses
* Polyline with no length should result in a circle or square.
> The HTML <canvas> element features seem to be oriented more towards
> displaying vector-based art than technical graphics; thereby missing out
> on easily supporting a large number of users. Why do I say this? My
> first attempt at using the element to support vector-based graphics
> produced by a program that dates back at least three decades was
> actually more difficult to implement in a <canvas> element that it was
> on an HP pen plotter many years ago.
> Even though I quickly became a fan of the HTML5 element because of the
> ease with which I could interface with standard HTML documents and
> dashed lines, Hershey/vector fonts, even-odd polygon fill rules, and
> points. And yet gradient fill patterns, opacity control, image
> manipulation, and complex clipping regions were all supported (which I
> consider more advanced graphic features than a dashed line!).
> Yet I found I could quickly create server-side applications or
> found at http://home.comcast.net/~urbanjost/canvas/vogle4.html shows
> some simple XY plots containing simple labels, dotted grids, and dashed
> lines. This was done with the help of a server-side library, but the
> But everyone does not have routines laying around to do sofware-based
> dash codes, ASCII text strings, and grids. However, it looks like others
> have already raised these issues except for the topic of points
> (although I don't think anyone brought them up together, pointing out
> that they are all common elements of any simple XY-plot utility).
> Since the other topics have already been breached, I'll make my point
> about points!
> It is common practice in many graphic formats to represent a polyline
> composed of a simple "move2(x,y)" or "move2(x,y) draw2(x,y)" as a point.
> Another common solution is to provide a marker(x,y,"name",sz) routine
> that can draw various markers at points.
> It is quite common for a technical plot to be a so-called "scatter" plot
> where the data is marked purely by marker symbols or points. It is also
> common to unpredictably have a polyline be just a single point. If dashed
> lines are going to be supported, it is important to note that almost all
> dash code models support points as part of the dash-code pattern. Every
> graphing utility I can thing of supports dotted grids, and so on. Points
> are so common in technical plots that I strongly prefer that a polyline
> that has no length is represented as a filled circle with a diameter
> equal to the current line width or as a square centered on the point
> with an edge length equal to the current line width.
> Inconveniently, the current <canvas> standard says to ignore a polyline
> with no length. This means any code drawing simple curves has to detect
> such lines and render them as circles or squares or give them a false
> non-zero length.
> If others have reasons for not wanting to render lines with zero length,
> perhaps the solution would be a new graphics state option that would let
> you toggle between the two behaviors.
> The other surprise was that there was no display list or object
> definition capability. Simple plots usually don't make much use of
> these, except to define a marker style, but I find them invaluable in
> nearly any nteractive
> All that being said, I find the <canvas> element a welcome and overdue
> addition to the Web ( I actually liked VML better than either SVG or PDF
> or CANVAS because there was a common editor, browser, and drawing
> utility immediately available that supported it, but I'm practical
> enough to know VML is now destined to be a proprietary MS-centric
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