Asynchronous Loading

Asynchronous loading

The originals decode every picture and parse every model before LoadTexture, LoadImage, LoadMesh or LoadAnimMesh return. BlitzLLVM can instead read the file, return a handle at once and decode on worker threads, so that the program can do other setup in the meantime. It is off by default, so a program behaves as in the original unless it turns it on with AsyncLoading or the environment variable BLITZLLVM_ASYNC_LOAD=1.

Everything that needs the picture waits for it by itself, so a program does not have to change: drawing, TextureWidth, ImageWidth, ReadPixel and the rest. TextureReady and ImageReady only ask, for programs that want to show a loading screen or to measure.

A missing file or a file that is no picture still gives 0 from the load command, because the file is read and its header checked right away. The file is read when the command is called, so it can be deleted or replaced afterwards. What cannot be known until decoding is whether the picture is complete: a file with a valid header that cannot be decoded raises an error the first time the picture is used. Cube maps (flag 128) and sheets of frames are loaded without threads.

Models

LoadMesh and LoadAnimMesh read the file and check its header (.b3d and .3ds) when they are called, give the handle of an empty entity, and parse the file on a worker thread, which also makes the vertices, indices and normals of its surfaces. The entity is filled in the first time anything asks for it, which is any command that takes the entity, or when Flip finds the parsing done. So m = LoadMesh("a.b3d") : PositionEntity m, 1, 2, 3 waits for the model right there, while a loop that loads fifty models and uses them afterwards parses them side by side. The textures of a model are loaded when it is built, and with asynchronous loading on they are decoded on the worker threads as well. EntityReady says whether a model is built and its textures are done.

A missing file, a .x file (still an empty model) and a file that is no model give the same result as without asynchronous loading. A .b3d or .3ds file that has a valid header but cannot be read stops the program at its first use with an error, and not as a 0 from the load. LoadAnimSeq is not moved to other threads.

Saving pictures has its own switch, AsyncSaving, see Saving pictures.