GraphicsContext and export to vector format files

[Bruce Johnson]

I think were’ not too far different in our ideas, but I think the practical odds of getting this implemented are much higher if the existing GraphicsContext methods are the base for the interface I propose.  I think (but could be wrong) that in fact the GraphicsContext was modeled after the HTML 5 canvas so in that sense it forms a good base for what you suggest.  One could write code that drew to the Canvas, to an HTML 5 canvas, to graphics files etc.  It’s just that now, with GraphicsContext being a final class rather than non-final or an interface, one can’t do any of this.

Bruce



> On Nov 2, 2020, at 9:17 AM, Michael Paus <mp at jugs.org> wrote:
> 
> Hi,
> I very much like the idea in general but I think it falls too short.
> Such an interface should not be tied to any existing graphics
> framework. Instead it should be just pure Java. This would allow
> to write complex graphics rendering code for a lot of different
> platforms and not only platforms where JavaFX already exists
> and can be used. Just think of the Android canvas or, via cross-
> compilation, even the HTML 5 canvas.
> Just my two €ent.
> Michael
> 
> Am 02.11.20 um 14:18 schrieb Bruce Johnson:
>> A variety of packages (for example,  VectorGraphics or JFreeSVG) exist that allow redirecting Java2D drawing to output other than the Java2D canvas.
>> 
>> These work by extending java.awt.Graphics2D.  By passing the extended Graphics2D object into a paint method, output can be redirected to a file (.svg, .pdf, etc.).
>> 
>> The GraphicsContext class of JavaFX serves a similar function to Graphics2D of java.awt, but because it is a final class it cannot be extended to create similar functionality as found in VectorgGraphics or JFreeSVG.
>> 
>> This is a serious limitation (at least as far as I can tell) to JavaFX applications.  It would be highly desirable to be able to redirect drawing on a Canvas to other output formats such as vector graphics files (.svg, .pdf etc.).
>> 
>> I currently work around this by using composition.  I have a Java interface that has most methods of GraphicsContext.  Then a GraphicsContextProxy class implements the interface and contains an instance of GraphicsContext.  This class is used for drawing to the Canvas.  I’ve then created a SVGGraphicsContext and PDFGraphicsContext that implement the interface and these can be used to draw to .svg or .pdf files.
>> 
>> This works, but means that all code that draws on the canvas has to be rewritten to take the GraphicsContextInterface rather than the normal GraphicsContext.
>> 
>> It would be much simpler if
>> 	1) GraphicsContext was not final and could be extended.
>> 	or
>> 	2) A GraphicsContextInterface existed that GraphicsContext implemented.  Developers could then have alternative GraphicsContext implementations that implemented that interface.  This would require canvas drawing code to be written to use the interface, but would still be very useful.
>> 
>> Either solution could (I think) be easily implemented in JavaFX without breaking existing code and add a significant advance to the toolkit.
>> 
>> If there are alternative solutions to the problem, that would allow exporting canvas drawing to vector graphics files without requiring a change to the code that draws to the canvas, I’d appreciate hearing them.
>> 
>> — Bruce
>> 
>