How to add texture via scripting

Question

I'm reading an addon's code. It's used to automatically add an image(texture) on an model and render out an image. User can feed any image and model. Here is the code snippet：

    def addMaterialImg():
    for img in bpy.data.images:
        name = img.name_full
        material = bpy.data.materials.new(name= name)
        material.use_nodes = True
        #create a reference to the material output
        material_output = material.node_tree.nodes.get('Material Output')
        Principled_BSDF = material.node_tree.nodes.get('Principled BSDF')                                 

        texImage_node = material.node_tree.nodes.new('ShaderNodeTexImage')
        texImage_node.image = img
        #set location of node
        material_output.location = (400, 20)
        Principled_BSDF.location = (0, 0)
        texImage_node.location = (-400, -500)

        material.node_tree.links.new(texImage_node.outputs[0], Principled_BSDF.inputs[0])
        material.node_tree.nodes["Principled BSDF"].inputs['Specular'].default_value = 0
        material.node_tree.nodes["Principled BSDF"].inputs['Roughness'].default_value = 0.5
        mat = bpy.data.materials.get(name)
        mat.blend_method = 'CLIP'
    return mat

What I'm confused about is: how does the addon find the particular mesh which I want to add image(texture) on?

Here it seems the addon follows the node location. If so, what the value (400,20) (0,0) (-400,-500) mean?

I need to make it clear, because I'm creating models for it. There must be some standards should be followed.

The developer figured out that the models here should be merged into one mesh so the script could operate on them. I checked the sample model from the developer, there are 2 material slots. The image mesh is on one of them.

So the addon should know which material slot and which node, right? How?

Answer 1

When you select objects, either in the 3D viewport, or the outliner, the last one you select becomes the active object. By using bpy.context.active_object, the add-on is using that object. It is also assuming that there isn't already a material assigned to slot 1 of the object, so it is putting the material in that slot. For it to be completely useful, the add-on probably has a way of assigning the material in slot 1 to selected faces on your mesh.

On the other hand, slot 0, the first slot, is important because all faces of the object that you don't explicitly assign a material to will be assigned to that slot by default.