MS RFC 87: Bitmap pattern support¶

Date:: 2013/01/14
Author:: Tamas Szekeres
Contact:: szekerest at gmail.com
Status:: Draft
Version:: TBD

1. Overview¶

With this addition we could easily define brush patterns which are aware of color and backgroundcolor settings and rendered equally well with the various kind of renderers. Currently we have no such option to achieve the same result, by using vector symbols we can not provide the same look for most of the renderers (agg, cairo), due to the possible antialiasing behaviour of the line drawings.

Bitmap patterns would be defined as symbols of type PATTERNMAP according to the example below:

SYMBOL
  NAME "mapinfo-brush-54"
  TYPE PATTERNMAP
  IMAGE "|10000010|01000100|00111001|01000100|10000010|00000001|00000001|00000001"
END

This symbol will provide the following brush fill:

Bitmap patterns can be defined with any size according to length of the rows specified in the IMAGE section.

Bitmap patterns are non scalable, cannot be rotated, and the gap is always set to zero. The patterns are aware of COLOR and BACKGROUNDCOLOR defined in the STYLE section.

2. Proposed Solution¶

We will define a new symbol type PATTERNMAP, maplexer.l will be modified to be aware of this new keyword. The new symbol type would be rendered in the same way a the PIXMAP symbols. The mos significant difference is that the tile image is created on the fly instead of loading the image from file.

3. Implementation Details¶

In mapsymbol.c msPreloadImageSymbol will be modified to initialize the raster buffer with the proper size according to the bitmap specified in the IMAGE section. In maprendering.c getTile will be modified to render the image:

case (MS_SYMBOL_PATTERNMAP):
      if(msPreloadImageSymbol(renderer,symbol) != MS_SUCCESS) {
        return NULL; /* failed to load image, renderer should have set the error message */
      }
      msCreateBitmapSymbol(symbol, s);
      renderer->renderPixmapSymbol(tileimg, p_x, p_y, symbol, s);
      break;

The new function msCreateBitmapSymbol will process the IMAGE section in the symbol definition and set the pixels according to the STYLE colors.

computeSymbolStyle (in maprendering.c) will be modified to set up colors scale gap and rotation parameters before the rendering is taking place.

4. Files Affected¶

maplexer.l, maplexer.l: Add PATTERNMAP keyword

mapsymbol.h: Add MS_SYMBOL_PATTERNMAP enum value

mapsymbol.c: Modify the parser, writer and msPreloadImageSymbol

maprendering.c: Add msCreateBitmapSymbol, modify computeSymbolStyle, getTile etc.

mapdraw.c: Modify msDrawVectorLayer, msDrawShape to be aware of MS_SYMBOL_PATTERNMAP

5. Bug ID¶

https://github.com/MapServer/MapServer/issues/4561

Contains link for the sample implementation.

6. Backwards compatibility issues¶

None expected, new functionality.

7. MapScript changes¶

MS_SYMBOL_PATTERNMAP will be exposed as a new symbol type.

8. Voting history¶

TBD.