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Now that we have one mesh instanced twice with the same shader, how to do we override the shader of one of the two instances ? It is usual in scene graph APIs to have a hierarchical assignment strategy where the leaf nodes inherit parent attributes. In such scenarios, overriding of attributes is possible only on the child nodes. In our case, the child node has a shader assigned to it already. Thankfully, NSI allows you to perform top-down overrides by specifying priories on connections. We can connect an attribute node, along with its shader, on the instance transform node.
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/**
Create another simple shader node using the standard OSL "emitter" shader.
User default shader prameters.
*/
nsi.Create( "simpleshader2", "shader" );
nsi.SetAttribute( "simpleshader",
NSI::CStringPArg("shaderfilename", "emitter") );
const char *k_attributes_override = "attribute override";
nsi.Create( k_attributes_override, "attribute" );
/* Default priiority is 0, so 1 will override */
nsi.Connect( k_simpler_shader2, "", k_attributes_override, "surfaceshaders",
NSI::IntegerArg( "priority", 1) );
/*
Connecting the attributes to the second instance transform will
override the shader below because of higher priority.
*/
nsi.Connect(
k_attributes_override, "", k_instance2, "geometryattributes" );
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Multi-Camera output, in One Render.
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