Python: How to Save UV Layout With Specific Background Color?

Question

select_obj(some_obj)
bpy.ops.object.mode_set(mode="EDIT")
bpy.ops.mesh.select_all(action='TOGGLE')
bpy.ops.mesh.select_all(action='TOGGLE')
# how to set background color of this image?
bpy.ops.uv.export_layout(filepath='uv_layout.png', size=(1024, 1024), opacity=1)
bpy.ops.object.mode_set(mode="OBJECT")
bpy.ops.object.select_all(action='TOGGLE')

The image looks like this (it has a transparent background):

However, I want to achieve a colored background like this:

I've tried to import PIL and do the image manipulation with this module, but it seems as if it isn't included in Blender.

Answer 1

It is not that hard to overwrite the function provide by the module itself (it is still in Python scope):

Caution:

The following code may now work as expect since source code is constantly changing. One should always look at matched source code and modify the "clear" color in used (the tuple (0.0, 0.0, 0.0, 0.0) )

import io_mesh_uv_layout
from io_mesh_uv_layout.export_uv_png import *

def new_export(filepath, face_data, colors, width, height, opacity):
    offscreen = gpu.types.GPUOffScreen(width, height)
    offscreen.bind()

    try:
        bgl.glClearColor(0.0, 1.0, 0.0, 0.9)  # Here, a green, 0.9 alpha background
        bgl.glClear(bgl.GL_COLOR_BUFFER_BIT)
        draw_image(face_data, opacity)

        pixel_data = get_pixel_data_from_current_back_buffer(width, height)
        save_pixels(filepath, pixel_data, width, height)
    finally:
        offscreen.unbind()
        offscreen.free()

io_mesh_uv_layout.export_uv_png.export = new_export  # Directly overwrite it

In your addon, you can provide a color picker(from a color float property) for user. And after updating the value, patch the original export function on the fly. There shouldn't be any tricky part and no performance issue at all.

---

A more complex method is to modify the uv layout export itself:

Which needs to modify the operator itself, kind of tricky but more flexible to use:

(Comment included)

Answer 2

If black background is good enough you could import the created image and remove the alpha channel.

select_obj(some_obj)
bpy.ops.object.mode_set(mode="EDIT")
bpy.ops.mesh.select_all(action='TOGGLE')
bpy.ops.mesh.select_all(action='TOGGLE')
# how to set background color of this image?
bpy.ops.uv.export_layout(filepath='uv_layout.png', size=(1024, 1024), opacity=1)

img = bpy.data.images.load("C:\\File\\Path\\Here\\uv_layout.png") #Import image. Remember to change filepath
img.alpha_mode = "NONE" #Ignore alpha channel
img.save() #Save the image

bpy.ops.object.mode_set(mode="OBJECT")
bpy.ops.object.select_all(action='TOGGLE')

Just make sure you change the filepath to point to your file.

This can be done manually in image editor from the Alpha drop-down menu by selecting None. Alpha Drop-down menu is under Image tab. Image tab visibility can be toggled by pressing n.