[AGG] Your opinion...

[George <geo...@ho...>]

Hi all,

another simple question (I hope). In principal this has to do with the 
best approach to my task.

I need to render groups of vectors (for a map) in different layers. The 
order is important and so is speed. Currently I am running through each 
"layer" and rendering its contents is particular order, however, as I 
cannot cache all the data to be rendered into memory (too much) I need 
to sequentially read vector by vector from the source and then discard. 
This makes it considerably slow because in essence I need to read each 
layer data from the source 2-3 times, one for the geometry itself 
(bottom-up), one for the labels (top-down) and if a line layer (road) 
another one for the outline (bottom-up). The 3rd one is tricky (which 
actually happens first) cause I wish to group outlines between layers so 
all outlines for all road categories to be rendered together and then 
the actual road color/fill.

My current thought now is to work on a image-layered approach as 
Photoshop does, where I read the data once but I can draw onto different 
pixmaps and in the end combine them keeping their Alpha transparency.

Would you say this is a good/fast approach to my problem and can I 
expect the same high quality image by doing copy_from ?

Thanks

George