Jorg’s Graphics Lecture Notes – 2. Basic openGL Programming 1
2. Basic openGL Programming
Global state
OpenGL is not object oriented!
It has a global state organized as a tree-like stack via ‘push’ and ‘pop’ separators.
image = GlobState(attributes; objects)
•Primitives: (what, shape node) points, line segments, polygons, pixels,
curves
•Attributes system state: (how, property) accum buffer, color, current,
depth buffer, enable, eval, fog, hint, lighting, line, list, pixel mode, point,
polygon, polygon stipple, scissor, stencil buffer, texture, transform, view-
port.
•2 matrix stacks:
glMatrixMode(GL PROJECTION ) Viewing: projection, clipping
glMatrixMode(GL MODELVIEW ) Transformation: rotate, scale, trans-
late
•events (input, error handling, network connection, etc.)
Example:
glClear()
glColor3f()
glBegin (GL_POINTS)
glVertex2fv()
glEnd (GL_POINTS)
glFlush()
OPENGL/1bufftst
Clipping and viewing volume
•glOrtho( left, right, bottom, top, near, far )
•camera always looks down negative z-axis.
•camera ‘views’ everything in the viewing volume (frustum) – also objects
‘behind’ the camera.
•glOrtho2D( left, right, bottom, top) = glOrtho( left, right, bottom, top,
-1, 1 )
