Changes between Initial Version and Version 1 of GSoC_SVG_Symbols_FIRST_DRAFT_OF_THE_MS-RFC

Timestamp:

Jul 12, 2009, 7:25:22 PM (15 years ago)

Author:

kiranvarma

Comment:

--

GSoC_SVG_Symbols_FIRST_DRAFT_OF_THE_MS-RFC

@@ +1 @@
+                                  
+                                     ==  MS RFC - SVG Symbol Support with AGG ==
+
+                                          Kiran Anjaneya Varma Alluri
+                                                July 12, 2009
+1     Overview.
+   Popular tools such as Inkscape generate SVG graphics natively. So far MapServer has not supported
+the SVG format, which leaves many users with the extra work of converting between formats. This
+RFC aims to introduce support for SVG graphics as an alternate method to de
+ne vector symbols in
+the MapServer symbolset.
+2     Method.
+The SVG parsing and rendering will be triggered by the following syntax:
+      
+{{{
+SYMBOL
+         TYPE VECTOR
+         FILE / path / to / f i l e . svg
+      END
+}}}
+
+The choice for using a SYMBOL for the task is to allow for the reuse of the SVG symbol easily within
+classes.
+3     Technical Overview
+In order to support the SVG format, we make use of the AGG library. The reasons for going with the
+AGG library are:
+   1. It has already been integrated into MapServer. While other popular libraries, such as Cairo, can
+      be used, they would require eort to integrate into MapServer and would further introduce many
+      dependencies into the MapServer code.
+   2. It is a very lightweight library and delivers performance equal to, and sometimes higher than
+      other popular libraries.
+
+There are some disadvantages that emerge from using the AGG library. Foremost, the AGG library
+has an incomplete SVG speci
+cation. To avoid having to reimplement the missing subset of the
+speci
+cation (which would, without a doubt, be a non-trivial task, and would add to the complexity
+of this RFC), we stick by the following techniques:
+   
+   1. A modular design is used, where the generation of the intermediate pixmap is done by a single
+      function so that it can be easily modi
+ed to adjust to a dierent library. Thus,using a pixmap
+      will allow us to use any rendering library.
+   2. The unimplemented subset of the SVG speci
+cation is clearly provided to users in the documen-
+      tation to prevent frustration on their side.
+                                                   1
+To implement this functionality, the following steps needs to be accomplished:
+   
+   1. Implement an SVG parser. For this, we directly make use of the SVG Viewer example provided
+      along with the AGG sources.
+   2. Write a single function to render a parsed SVG 
+le to a pixmap. The pixmap will be an inter-
+      mediate form that can then be rendered. The pixmap will be stored in cache memory to prevent
+      having to constantly be rasterized it every time a symbol is drawn.
+   3. Render the pixmap into the 
+nal image 
+le. This will be done using a mixture of the AGG and
+      GD libraries.
+   4     Files Added
+
+Finally, the SVG parsing and pixmap generation functions will be stored in source 
+files stored at
+
+{{{
+/ mapserver / r e n d e r e r s / agg / svg /
+}}}
+ 
+The 
+files within the above directory include the files for:
+    • SVG Parsing
+    • Trigger Function (based on Map
+file syntax)
+    • SVG to Pixmap generation
+All 
+files are within the C++ 'mapserver' namespace.
+
+5     Documentation
+The following documentation needs to be prepared for this project:
+   1. Missing SVG speci
+cation document.
+   2. Basic usage tutorial with examples.
+
+