Control node dropshadow shader (how to blur a texture with shaders?)

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Control node dropshadow shader (how to blur a texture with shaders?)

pigna

So I had this idea to try and draw a shadow for a texturerect control node. The idea is to have a blurry black version of whatever icon is displayed on the texture rect drawn behind the node itself, using the "shadow" shader in the next pass of the main material. I tried blurring the texture by running this in the fragment shader COLOR = textureLod(TEXTURE, UV, 10.0) but the texture doesn't change. Why?