GPU Driven Draws

GPU-driven draws

Experimental, off by default: BLITZLLVM_GPU_DRAWS=1 turns it on. It needs a GPU that can draw many indirect commands in one call (the same as the culling of big meshes, see Spatial-Grid for the CPU side of finding what is in view).

Normally the program makes the data of every draw (matrix, color, texture, lights) for every camera and every frame. Meshes that stay as they are for a few frames can be drawn in a cheaper way: their draws are made once and kept in a table, and a compute shader makes the draws of a camera from it. It moves each entry by where the camera is, leaves out the ones outside of the view and writes the commands, which are drawn with one indirect call for each group of entries that share their pipeline, texture and buffers. While a mesh is in the table the program does not look at it at all.

What is drawn does not change: the picture of a program is the same with and without it.

Which meshes go in the table

A mesh goes in the table after it has stayed untouched for four frames, and only if it is solid and stands alone: no parent, no EntityOrder, no fade, not a sprite, plane, terrain, level, animated or skinned mesh, no extra texture layers and no see-through surfaces. Everything else is drawn as before. EntityStatic changes the wait: with -1 a mesh is never put in the table, with 1 it goes in without waiting for the four frames (it still has to be solid and stand alone), and with 0, the default, the renderer decides as described. Cameras that look into a mirror draw everything the usual way.

What takes a mesh out of the table

Any command that takes the entity (moving it, coloring it, hiding it, freeing it, painting it, ...) takes that mesh out of the table, and it goes back in after four frames without being touched (a mesh with EntityStatic 1 that is moved, turned, scaled or re-parented goes back to EntityStatic 0; anything else that changes it is shown at once and it goes back in the next frame without the wait). These throw the whole table away, because every mesh depends on them: any change of a light, the vertices or paint of any surface, any command that takes a texture, WireFrame, and a change of Dither. When such a change happens every frame (an animated mesh, a program that changes a texture each frame) the table waits longer and longer before it is made again, so a scene that changes all the time is drawn the usual way.

Differences

TrisRendered does not count the triangles of the table.