XPLM_API void XPLMBindTexture2d( int inTextureNum, int inTextureUnit);
XPLMBindTexture2d changes what texture is bound to the 2d texturing target. This routine caches the current 2d texture across all texturing units in the sim and plug-ins, preventing extraneous binding. For example, consider several plug-ins running in series; if they all use the 'general interface' bitmap to do UI, calling this function will skip the rebinding of the general interface texture on all but the first plug-in, which can provide better frame rate son some graphics cards.
inTextureID is the ID of the texture object to bind; inTextureUnit is a zero-based texture unit (e.g. 0 for the first one), up to a maximum of 4 units. (This number may increase in future versions of x-plane.)
Use this routine instead of glBindTexture(GL_TEXTURE_2D, ....);