[parse_blend_file] depth of field

[wahn]

It would be useful to be able to specify depth of field (DOF) settings within the Blender scene and use those on the rs-pbrt side.
For .pbrt files those should work correctly already, but forparse_blend_file we still need a way how to translate the settings from the Blender UI to camera settings, which can be used for e.g. the struct PerspectiveCamera. Here an example from the Italian Flat scene:

In Blender version 2.79 the two settings in questions are shown here:

The depth of field distance can be used as parameter focaldistance directly, but Blender's f-stop value has to be translated somehow to PBRT's lensradius (in this example I used lensradius = 0.0125):

diff --git a/src/cameras/perspective.rs b/src/cameras/perspective.rs                                  
index 92c77db..72f9d98 100644                                                                         
--- a/src/cameras/perspective.rs                                                                      
+++ b/src/cameras/perspective.rs                                                                      
@@ -173,6 +173,10 @@ impl PerspectiveCamera {                                                         
         //     params.find_one_float(String::from("halffov"), -1.0);                                 
         // TODO: if (halffov > 0.f)                                                                  
         // TODO: let perspective_camera: Arc<Camera + Sync + Send> =                                 
+       // TMP                                                                                        
+        let lensradius: Float = 0.0125;                                                              
+        let focaldistance: Float = 5.6;                                                              
+       // TMP                                                                                        
         Arc::new(Camera::Perspective(Box::new(PerspectiveCamera::new(                                
             cam2world,                                                                               
             screen,                                                                                  

The best solution would be to look into Blender's source code to find a proper translation hint.

[wahn]

The focaldistance we need for PerspectiveCamera can be taken directly from Camera.YF_dofdist:

$ ./target/release/blend_info -n Camera.YF_dofdist ~/git/self_hosted/render_comparison/blend/italian_flat/italian_flat_v279.blend
Camera.YF_dofdist = 0_f32
Camera.YF_dofdist = 0_f32
Camera.YF_dofdist = 0_f32
Camera.YF_dofdist = 0_f32
Camera.YF_dofdist = 0_f32
Camera.YF_dofdist = 0_f32
Camera.YF_dofdist = 5.6_f32

[wahn]

From within Blender 2.79 you can access the aperture_fstop via Python:

>>> bpy.data.cameras['Camera_Table_Details'].cycles.aperture_fstop
2.0