blender: Extremely hacky fix for shaded viewport zoom

PERSP now works perfectly, assuming your viewport is either a square, or
wider than it is tall.
CAMERA perspective is still very wrong, and I have absolutely no clue
how to fix it. I trawled through Blender's code, found a weird 'magic
zoom' formula, asked the Blender devs about that, looked at some more
code, and I still have no clue how one is supposed to compute valid
camera parameters from everything correctly.
It now sort of, kind of, works. And the perspective type works
perfectly, as long as you size your viewport correctly.
Good enough for now!

bindings/blender_init.py

@@ -206,6 +206,7 @@ class CrayRender(bpy.types.RenderEngine):
 	cr_renderer = None
 	old_mtx = None
 	old_dims = None
+	old_zoom = None
 
 	def __init__(self):
 		print("c-ray initialized")
@@ -363,10 +364,14 @@ def render(self, depsgraph):
 		self.display_bitmap(bm)
 
 	def view_draw(self, context, depsgraph):
+		zoom = context.region_data.view_camera_zoom
 		mtx = context.region_data.view_matrix.inverted()
 		if not self.old_mtx or mtx != self.old_mtx:
+			self.old_mtx = mtx
+			self.tag_update()
+		if not self.old_zoom or zoom != self.old_zoom:
+			self.old_zoom = zoom
 			self.tag_update()
-		self.old_mtx = mtx
 		new_dims = (context.region.width, context.region.height)
 		if not self.old_dims or self.old_dims != new_dims:
 			cr_cam = self.cr_scene.cameras['Camera']
@@ -398,6 +403,15 @@ def view_update(self, context, depsgraph):
 		mtx = context.region_data.view_matrix.inverted()
 		euler = mtx.to_euler('XYZ')
 		loc = mtx.to_translation()
+		new_fov = math.degrees(context.space_data.camera.data.angle)
+		# I haven't the faintest clue why an offset of 32 degrees makes this match perfectly.
+		# If you know, please do let me know.
+		if context.region_data.view_perspective == 'PERSP':
+			new_fov += 32
+		else:
+			if self.old_zoom:
+				new_fov -= (self.old_zoom - 32)
+		cr_cam.opts.fov = new_fov
 		cr_cam.opts.pose_x = loc[0]
 		cr_cam.opts.pose_y = loc[1]
 		cr_cam.opts.pose_z = loc[2]