perspective
Defines the type of projection (
perspective or 
orthographic) 
used to project the layer 3D space into the screen 2D viewport. When not 
indicated, GAMGI uses the default. To change the default, select 
Layer->Config and read 
Help->Topics->Formats->Config->Layer.
Example: <layer ... perspective="yes"/> (default)
(defined in GAMGI_MESA_LAYER_PERSPECTIVE)
Allowed values: yes, no (optional)
top, near, far
Define the layer 3D viewing volume, before it is projected onto the 
2D viewport. The 
top parameter measures the height from the 
eye-center viewing direction (at the center of the viewport) to the 
top and bottom limits of the 2D viewport, thus defining the lateral 
borders of the 3D volume (the width is automatically determined from 
the window dimensions, in order to preserve the ratio width/height, 
otherwise the objects would be distorted).
The 
near and 
far parameters define the minimum and
maximum distances along the viewing direction at which objects must 
lie in order to be visible. 
near must be smaller than 
far.
When not indicated, GAMGI uses default values.
To change the default, select 
Layer->Config and read 
Help->Topics->Formats->Config->Layer.
Example: <layer ... near="1.0" far="1000.0" top="0.5"/> (default)
(defined in GAMGI_MESA_LAYER_NEAR, GAMGI_MESA_LAYER_FAR 
and GAMGI_MESA_LAYER_TOP)
Allowed values: positive real (optional)