[QGIS Commit] r14050 - docs/trunk/english_us/developer_cookbook/source

[svn_qgis at osgeo.org]

Author: wonder
Date: 2010-08-10 22:02:40 +0000 (Tue, 10 Aug 2010)
New Revision: 14050

Modified:
   docs/trunk/english_us/developer_cookbook/source/raster.rst
Log:
Explain refreshing of layers.


Modified: docs/trunk/english_us/developer_cookbook/source/raster.rst
===================================================================
--- docs/trunk/english_us/developer_cookbook/source/raster.rst	2010-08-10 21:09:07 UTC (rev 14049)
+++ docs/trunk/english_us/developer_cookbook/source/raster.rst	2010-08-10 22:02:40 UTC (rev 14050)
@@ -42,7 +42,7 @@
   3     PalettedColor                  "Palette" image drawn using color table
   4     PalettedSingleBandGray         "Palette" layer drawn in gray scale
   5     PalettedSingleBandPseudoColor  "Palette" layerdrawn using a pseudocolor algorithm
-  7     MultiBandSingleGandGray        Layer containing 2 or more bands, but a single band drawn as a range of gray colors
+  7     MultiBandSingleBandGray        Layer containing 2 or more bands, but a single band drawn as a range of gray colors
   8     MultiBandSingleBandPseudoColor Layer containing 2 or more bands, but a single band drawn using a pseudocolor algorithm
   9     MultiBandColor                 Layer containing 2 or more bands, mapped to RGB color space.
 ====== =============================== ===============================================================================================
@@ -57,6 +57,9 @@
 Multiband layers are typically drawn by mapping the bands to RGB colors. Other possibility is to use just one band for gray or pseudocolor
 drawing.
 
+The following sections explain how to query and modify the layer drawing style. After doing the changes, you might want to force update
+of map canvas, see :ref:`refresh-layer`.
+
 .. todo:: contrast enhancements, transparency (no data), user defined min/max, band statistics
 
 Single Band Rasters
@@ -105,6 +108,26 @@
   >>> rlayer.setColorShadingAlgorithm(QgsRasterLayer.PseudoColorShader)
   >>> # now set the shader
 
+.. _refresh-layer:
+
+Refresing Layers
+----------------
+
+If you do change layer symbology and would like ensure that the changes are immediately visible to the user, call these methods::
+
+   if hasattr(layer, "setCacheImage"): layer.setCacheImage(None)
+   layer.triggerRepaint()
+
+The first call will ensure that the cached image of rendered layer is erased in case render caching is turned on. This functionality is available from QGIS 1.4,
+in previous versions this function does not exist - to make sure that the code works with all versions of QGIS, we first check whether the method exists.
+
+The second call emits signal that will force any map canvas containing the layer to issue a refresh.
+
+In case you have changed layer symbology (see sections about raster and vector layers on how to do that), you might want to force QGIS to update the layer
+symbology in the layer list (legend) widget. This can be done as follows (``iface`` is an instance of QgisInterface)::
+
+   iface.legendInterface().refreshLayerSymbology(layer)
+
 Query Values
 ------------