A question

[cjrcjrljy]

i am reading the source code,but i cant understand the supports influence

    command.SetRenderTarget(mask);
    command.DrawRenderer(rend, paintMaterial, 0);

    command.SetRenderTarget(support);
    command.Blit(mask, support);

    command.SetRenderTarget(extend);
    command.Blit(mask, extend, extendMaterial);

but when i remove the code ' command.Blit(mask, support);' , i find it can`t work