06 - OpenGL

Question 1

What are the “Naming Conventions” for “OpenGL Functions”, “OpenGL Constants”, “OpenGL Types”

Answer 1

OpenGL Functions => gl
OpenGL Constants => GL_
OpenGL Types => GL

Question 2

Why are “GL_POINTS” and “GL_LINES” ugly? How to fix it

Answer 2

• infinity width => no anti-aliasing
• fix: use thin triangles

Question 3

How does the “Vertex Shader” work

Answer 3

• transform each vertex individually (e.g. “Gouraud Shading”)
  => better for transformations (only vertices of object must be moved, not all pixels in a fragment)
• can’t add or delete vertices
• input: vertex with attributes
• output: vertex with attributes

Question 4

How do the “Primitive Assembly” and “Tessellation Shader” work

Answer 4

“Primitive Assembly”
- input: n vertices
-> compose requested primitives
-> special case: GL_PATCH

“Tessellation Shader”
- uses GL_PATCH
- how should patches be subdivided
- how should the result be shaded

Question 5

How does the “Geometry Shader” work? What other parts (not programmable) work with it?

Answer 5

• extend, remove, transform primitives
• also:
  – clipping (result will be de-homogenized)
  – rasterization (outputs fragments)

Question 6

How does the “Fragment Shader” work? What other parts (not programmable) work with it?

Answer 6

• input: 1 fragment
• output: 0-1 fragments
• can discard
• per-pixel shading (e.g. Phong-Shading)
• per-pixel sampling (e.g. volume rendering -> ray casting)

-also:
– per fragment operations

Question 7

What is the “Transform Feedback”

Answer 7

• writes result of geometry processing to a buffer
• buffer can be put into the pipeline by CPU

Question 8

How does the “Compute Shader” work

Answer 8

• input: indices
  => called by indices
• execution of compute shader organized in grid of workgroups
• indices say what workgroups run with what threads
  => massive parallel execution

IMPORTANT: Not in the pipeline