Light Blocker HtoA:
How to create a light blocker for HtoA houdini 16.5 just like MtoA
1-Create Arnold Light
2-Create a box and name it : "lightblock_1"
3-In your arnold light Filters click on the arrow to enter the shopnet
4-Create a light blocker and link it to the light filter1
5-Edit the parameter interface of the light Blocker by adding an Integer and name it "pram" and label it "Selection"
6-Set the Selection value to "1"
7-In the Geometry Matrix from the light blocker change these rows by the value mentioned below:
a) row 1 col 1: ch("../../../../lightblock_"+ch("parm")+"/sx")
b) row 2 col 2: ch("../../../../lightblock_"+ch("parm")+"/sy")
c) row 3 col 3: ch("../../../../lightblock_"+ch("parm")+"/sz")
d) row 4 col 1: ch("../../../../lightblock_"+ch("parm")+"/tx")
e) row 4 col 2: ch("../../../../lightblock_"+ch("parm")+"/ty")
f) row 4 col 3: ch("../../../../lightblock_"+ch("parm")+"/tz")
g) row 4 col 4: 1
8-In your geometry box named "lightblock_1", uncheck all the checkboxes in the visibility tab ( so the geometry doesn't show up in the render, but shows up in the viewport)
9-Now by moving and scaling the box in your viewport it will move the light blocker accordingly
10-You can duplicate the box and it should be named: "lightblock_2" and also duplicate the light blocker in the light shopnet and link it to the second filter and set its "Selection" to 2
11-Move the second box and it should make a new light blocker and work just fine.