What is the "OpenGL State Machine"? -

my brain tends favor structuring concepts in hierarchical, object-oriented, component-like ways. unfortunately, preventing me understanding opengl--and suspect source of confusion in misunderstanding of "opengl state machine" is. got graphics pipeline, specific individual program objects draw user's graphical components, right?

• what master state machine?
  • is opengl api, or frame i'm trying draw, or user defines--like pipeline?
• what different states can exist in?
  • is event-driven?
• what inputs affect different states machine can in?
• can hierarchical, oop concepts applied state machine?

this broad question, i'll give overview.

• what master state machine?

the state machine combination of complete opengl api , selected rendering context. rendering context contains of states makes state machine, while opengl api provides inputs change these states.

• what different states can exist in?

there many list. example, capabilities toggled glenable , gldisable (e.g. gl_texture_2d, gl_fog, gl_blend) part of state. name of current texture set glbindtexture; name of current shader program gluseprogram; contents of modelview , projection matrices plus state of glmatrixmode tells matrix glmultmatrix (etc.) calls affect; , on, part of state

• what inputs affect different states machine can in?

the initial state of machine given opengl specification, modulo gpu drivers. inputs can put machine different state calls opengl api.

• can hierarchical, oop concepts applied state machine?

this question vague. "hierarchical, oop concepts"?

it's possible take object-oriented approach wrapping opengl api. can create "texture" object class allocates texture name using glgentextures when initialized, , provides methods uploading texture image or changing texture parameters call glbindtexture before calling relevant apis methods. approach tricky still have keep track of current state through object , sub-object method calls.

opengl provides several "stacks" (vis. glpushmatrix, glpushattrib) meant manage hierarchies of objects. pushing part of current state onto stack, calling methods of child object, , popping state off of stack, can restore state 1 expected parent object.

the general object-oriented approach using opengl api through scenegraph - directed, acyclic graph of objects, each object represents change state machine's state. object pushes 1 or more opengl stacks, applies state using opengl api calls, calls methods of child objects, , pops off of opengl stacks restore previous state.