[Bf-cycles] Correct way to set-up UV channel for a texture?

[Gareth Morgan]

So I am setting up a shader that reads from an ImageTextureNode in Cycles:
ccl::CheckerTextureNode *img = new ccl::CheckerTextureNode();
img->input("Color1")->set(ccl::make_float3(0.0, 0.8, 0.0));
img->input("Color2")->set(ccl::make_float3(0.0, 0.2, 1.0));
img->input("Scale")->set(2.0f);

I have added my UVs to the mesh like this (I have verified my UVs are
correct):

ccl::Attribute *attr_vUV = mesh->attributes.add(ccl::ATTR_STD_UV,
ccl::ustring("UVMap"));
ccl::float3 *fUV = attr_vUV->data_float3();
for (int i = 0; i < verts_size; i++)
{
fUV[i].x = UVs[i * 2 + 0];
fUV[i].y = UVs[i * 2 + 1];
fUV[i].z = 0.0f;
}


I then add UVMap node to the graph like this:
ccl::UVMapNode *uvm = new ccl::UVMapNode();
uvm->attribute = ccl::ustring("UVMap");
graph->add(uvm);
And connect it to the rest of the shader like this:
graph->connect(uvm->output("UV"), img->input("Vector"));
graph->connect(img->output("Color"), diffuseBrdfNode->input("Color"));

I've tried various different variants of this (assuming 2D UVs, not setting
the UVMapNode attribute, etc) the result is always very broken image (see
simple rectangle example attached).

Is there a step I am missing to correctly setting up the UVs?
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