[Hgengine-devs] Texture re-binding

[Charles L. <ch...@cn...>]

Devs,

I have been examining the pipeline for textures.  I have found that
there is a large slow down whenever binding/unbinding textures.  I also
feel that there is little need to have the textures always clean up
after themselves, as it would enable a scene optimizer to group like
objects.  Simply by asking "is the current texture the one that is
active right now" we can avoid having to disable textures and re-deploy
them when done.  In a case like the field of lamps, we are able to
bypass the field.  It would also make it possible to have the texture be
a persistent item, and having it pass on to its children.

I propose:
  We do not unbind textures from OpenGL (until in the future we have an
option where a texture is a some sort of TEXTURE OFF thing)
  We store a static pointer to the currently OpenGL binded texture. 
When we bind a texture, we set that.  When we encounter a texture that
has already been set, take no action.

By performing this, the GL call count was less than half (now it's just
over 1k per scene)

I ran a few tests where I made the window small, thus avoiding pixel
fill time.


Without profiling, dumb textures:
FPS: 1089.498779, VBO batches 95.000000, TBinds 94.000000, VBinds 5.000000

Without profiling, smart-ish textures, smart matrixing:  (Textures bind
always, but never unbind) (smart matrix means only updating the matrix
info if the object has assets attached to it)
FPS: 1449.908691, VBO batches 95.000000, TBinds 5.000000, VBinds 5.000000

Without profiling, smart textures: (Textures never unbind, and only bind
when needed)
FPS: 1667.601440, VBO batches 95.000000, TBinds 5.000000, VBinds 5.000000

Without profiling, smart textures, smart matrixing:
FPS: 1759.813477, VBO batches 95.000000, TBinds 5.000000, VBinds 5.000000


Charles