I’d like to know if in Unity3d is possible to change an image at runtime (e.g. drawing a rect on an image or merging two images) and assign it to a texture a runtime
This is possible for example in java, is it possible in Unity3d too?
Yes, it is possible, but doing direct changes on to a texture with per-pixel edits is extremely slow. Depending on what you want to do, you probably want to use a special shader for this kind of work (fading from one texture to another is extremely easy, and fast, like this).
no, I don’t want that textures changes during game, but I only want to work on images during game loading, for example if I have an image with a red background, I want to draw on it a text (depending from some condition), and then use this image as texture in a material assigned to an object. then this texture will remain the same for all the game