For loading GFX, the game uses the sprite system. Sprites are code definitions that attach a name to an image file, as well as optionally adding additional information, such as animation, the amount of frames, the way that the image will be loaded, and so on. This means placing an image into the gfx folder isn't enough for it to work, a sprite has to use that image file as well. Sprites are defined in any /Hearts of Iron IV/interface/*.gfx file (this is separate from gfx/interface/), opened with a text editor. To create a new .gfx file, a text file can be created and renamed to change the extension (on Windows, the Windows Explorer needs to show the extensions, which it doesn't by default). In particular, sprites are defined within a spriteTypes = { ... } block, as to separate from fonts and map arrows also defined in that folder, while the simplest sprite with the least mandatory properties is a spriteType = { ... }. The simplest sprite definition looks like the following:
spriteTypes = {
spriteType = {
name = GFX_first_sprite # In some cases, beginning with GFX_ is mandatory for it to work.
texturefile = gfx/interface/folder/filename.dds # The folder and filename don't matter, as long as they are correct
} # Only the forward slash '/' (can be doubled as '//') can be used to separate folders.
spriteType = { # The image doesn't have to be .dds, as .tga and .png are acceptable.
name = GFX_second_sprite
texturefile = gfx/interface/folder2/filename2.dds
noOfFrames = 2 # Splits the image into 2 halves, which may be switched between dynamically in GUI
}
} In this case, this creates a sprite with the name of GFX_first_sprite and attaches the /Hearts of Iron IV/gfx/interface/folder/filename.dds image to it, and a second sprite similarly. The second sprite will be split into 2 frames: this is decided by having the left half of the image as the first frame and the right half as the second frame (more frames would further split the image horizontally). This doesn't make the sprite animated, just turns on the option to switch between the two halves as needed. GFX_second_sprite:1 serves as a reference to the first frame, and GUI can be set up to change the shown frame depending on context, such as with radio stations. In order to add animation, a frameAnimatedSpriteType is used.
It's never mandatory to copy a base game file to change a sprite. If there are duplicate definitions of a sprite with the same name in different files, the game will prioritise the one that would be evaluated later, based on the filename, and the older sprite will be ignored in entirety. This can be ensured by beginning the replacement file's name with a symbol late in the ASCII character table. Typically the lowercase letter 'z' is used for this purpose. For example, to change the amount of frames in GFX_idea_traits_strip to 10, it is possible to define a sprite with that name with 10 frames in the mod's modname/interface/zz_replace.gfx file instead of copying over the base game file. Since most .gfx files define integral parts of the user interface, copying them over can lead to the mod's loaded files missing sprites upon a major game update, which would appear in-game as the default image, which is the error dog by default. As to ease the burden of needing to check the interface files, it's best to never copy over .gfx files, unless more additions would be actively harmful to the mod, such as with interface/subuniticons.gfx