Document the return value of choose() and how it is useful.

[nageru-docs] / theme.rst

diff --git a/theme.rst b/theme.rst
index 7ce42f07dd9e2b54bfb30fc466baca1156c99ae1..7fbe735b1ce6f081947603c1f4c0386b217f1982 100644 (file)
--- a/theme.rst
+++ b/theme.rst
@@ -83,6 +83,7 @@ produces a mix of them; Movit's *MixEffect* is exactly what you want here::
   local input1 = scene:add_input()
   input1:display(1)
 
+  -- Note that add_effect returns its input for convenience.
   local mix_effect = scene:add_effect(MixEffect.new(), input0, input1)
   scene:finalize()
 
@@ -146,8 +147,8 @@ scaler before mixing; *ResampleEffect* provides one::
   local input0 = scene:add_input()
   input0:display(0)
   local input0_scaled = scene:add_optional_effect(ResampleEffect.new())  -- Implicitly uses input0.
-  scene_or_input.resample_effect:set_int("width", 1280)  -- Could also be set in get_scene().
-  scene_or_input.resample_effect:set_int("height", 720)
+  input0_scaled:set_int("width", 1280)  -- Could also be set in get_scene().
+  input0_scaled:set_int("height", 720)
   input0_scaled:enable()  -- Enable or disable as needed.
 
   local input1 = scene:add_input()
@@ -174,8 +175,8 @@ directly by the GPU) that instead. The scaling is set up like this::
   local input0 = scene:add_input()
   input0:display(0)
   local input0_scaled = scene:add_effect({ResampleEffect.new(), ResizeEffect.new()})  -- Implicitly uses input0.
-  scene_or_input.resample_effect:set_int("width", 1280)  -- Just like before.
-  scene_or_input.resample_effect:set_int("height", 720)
+  input0_scaled:set_int("width", 1280)  -- Just like before.
+  input0_scaled:set_int("height", 720)
 
   -- Pick one in get_scene() like this:
   input0_scaled:choose(ResizeEffect)
@@ -183,15 +184,28 @@ directly by the GPU) that instead. The scaling is set up like this::
   -- Or by numerical index:
   input0_scaled:choose(1)  -- Chooses ResizeEffect
 
-Note that add_effect returns its input for convenience. All alternatives must
-have the same amount of inputs, with an exception for IdentityEffect, which can
-coexist with an effect requiring any amount of inputs (if selected, the IdentityEffect
-just passes its first input unchanged).
-
 Actually, add_optional_effect() is just a wrapper around add_effect() with
 IdentityEffect as the other alternative, and disable() is a convenience version of
 choose(IdentityEffect).
 
+All alternatives must
+have the same amount of inputs, with an exception for IdentityEffect, which can
+coexist with an effect requiring any amount of inputs (if selected, the IdentityEffect
+just passes its first input unchanged). Similarly, if you set a parameter with
+set_int() or similar, it must be valid for all alternatives (again excepting
+IdentityEffect); if there is one that can only be used on a certain alternative,
+you must set it directly on the effect::
+
+  local resample_effect = ResampleEffect.new()
+  resample_effect:set_float("zoom_x", 1.0001)  -- Not valid for ResizeEffect.
+   
+  local input0_scaled = scene:add_effect({resample_effect, ResizeEffect.new()})
+  input0_scaled:set_int("width", 1280)  -- Set on both alternatives.
+  input0_scaled:set_int("height", 720)
+
+  -- This is also possible, as choose() returns the chosen effect:
+  input0_scaled:choose(ResampleEffect):set_float("zoom_y", 1.0001)
+
 Actually, more versions are created than you'd immediately expect.
 In particular, the output format for the live output and all previews are
 different (Y'CbCr versus RGBA), which is also handled transparently for you.