All of our current layer view colour schemes are properties of a line, not of a vertex. The line has a single feedrate, a single line type, a single layer thickness, a single material colour and a single width. This is even limited by the g-code specification itself, which is unable to represent lines with varying line width. However, we store this information in the vertices, the vertex data being the only data sent to layer view since layer view is sent as polylines to the shader.
This change makes the entire line take on the colour scheme of the vertex where its representative data is stored. This data is intended for the line, not just for that vertex, so it makes sense that the entire line listens to the data of the correct vertex, not just the nearest vertex of the line's endpoint.
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