The end result is that changing the set of layers could realistically be a hundred times slower than the ideal case (storing the layers in video memory, and having the GPU compose them). Whenever the layer stack changes, it has to call an external program (g.pnmcomp) to compose the layers into a single image, which it then loads and displays. Instead, it has to store the layers as image files. load all of the layers, then just redraw whenever the layer stack changes. So you can't take the approach that you would in a C program, i.e. The main issue here is that Tk doesn't support masked, true-colour images it supports GIF (masked, 256 colours) or PPM (true-colour, no mask). For example, if a user add a layer, it should be automatically added to the Map, triggering the "draw" or the "re-render" action.
IMHO a modern GIS should automatically manage the display of the layers as the user interact with the Layer Manager. Status bar Indicates, from left to right, the location of the cursor (x and y coordinates), the scale of the map, the value and position (row, column) of a gridcell, and the distance between two points. I know it's too generic, but I really can't be more accurate in the description. Finally, look in the status bar at the bottom of the main window and check that. You can see this case in the image attached: the points aren't visible. study area data from various sources, such as CAD drawings or GIS files. sometimes I can see the things as they should. If I randomly switch on and off, move up and down, the layers. Sometimes (not always) the layer (2) hides layer (1). magically it gets workin correctly: I see the whoole stack in the map window. If I move up and down various times the vector in the layer manager. If I switch off raster (2) I can see the points again. It happens that (2) hides the points layer. I try to describe some situations I have faced using 1,2,3.,n to define the layers from bottom to the top of the stack: If I add various rasters and vectors I often have problems in the visualization. I find difficult to describe this problem because it seems to happen randomly.
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