Minor fixes to previous commit

* Restrict clear to frame
* Restrict viewport to frame, as it used to be
* Moved viewport clearing to render code

demo.srd

@@ -21,9 +21,6 @@
 	(call bloom-init)
 	(call combine-init)
 	(call fxaa-init)
-
-	(viewport 0 0 $width $height)
-	(clear 0 0 0 0)
 )
 
 (frame
@@ -426,6 +423,9 @@
 (fn fxaa-render (in-image)
 	(profiling "FXAA"
 		(main-output)
+		(viewport 0 0 $width $height)
+		(clear 0 0 0 0)
+
 		(use-pipeline pl-fxaa)
 		(use-texture 0 in-image smp-fxaa)
 		(uniforms prg-fxaa 2

opast.hh

@@ -335,7 +335,8 @@ class T_ClearInstrNode : public A_InstructionNode
 
     public:
 	T_ClearInstrNode( T_InstrListNode& parent ) noexcept
-		: A_InstructionNode( OP_CLEAR , parent )
+		: A_InstructionNode( OP_CLEAR , parent ,
+				E_InstrRestriction::INIT )
 	{ }
 
 	void addComponent( P_ExpressionNode expr ) noexcept
@@ -962,7 +963,8 @@ class T_ViewportInstrNode : public A_InstructionNode
 
     public:
 	T_ViewportInstrNode( T_InstrListNode& parent ) noexcept
-		: A_InstructionNode( OP_VIEWPORT , parent )
+		: A_InstructionNode( OP_VIEWPORT , parent ,
+				E_InstrRestriction::INIT )
 	{ }
 
 	void setParameter( const E_Parameter p , P_ExpressionNode height ) noexcept