Core Profile and Compatibility Profile

The Key Versions to Revolute The OpenGL

  • OpenGL 3.0 introduced deprecation model to gradually remove legacy functions.
  • OpenGL 3.1 removed the deprecated functions and the remaining part forms the Core Profile.
  • OpenGL 3.2 introduced Compatibility Profile to maintain backwards compatibility.

Core Profile OpenGL

  • Have access to later OpenGL functionalities
  • More suitable for modern GPU
  • Many familiar functionalities removed
  • All rendering must use shaders
    • A shader is a program loaded and executed in a stage of the rendering pipeline
    • The shader is a user program which means that the users have to/can define their own shaders to realize the rendering

OpenGL Pipeline

A simplified view of OpenGL Graphics Pipeline is shown as follows:

Vertex Shading

  • Excuted per vertex
  • Produces vertex NDC (normalized device coordinates) coordinates

Tesssllation

  • Tessellation Control Shader (TCS)
    • Executed per patch vertex
    • Receives patch vertices (control points) from vertex shader
    • Generates tessellation output patch vertices to pass to the Tessellation Evaluation Shader (TES)
    • Specifies tessellation level factors
    • Optional
  • Tessellation Primitive Generator (TPG)
    • Receives tessellation level factors from TCS
    • Performs tessellation and generates tessellation coordinates for the resulting primitives and pass them to the Tessellation Evaluation Shader (TES)
    • not programmable
  • Tessellation Evaluation Shader (TES)
    • Executed per tessellation coordinate
    • Receives patch vertices (control points) from TCS
    • Computes vertex position from tessellation coordinate
    • Optional

Geometry Shading

  • Executed per primitive
  • Receives complete primitive (as arrays of vertices/attributes) from earlier stage
  • Outputs zero primitive (culling) or more primitives (geometry amplification)
  • Can output primitive type different from input
  • Optional

Primitive Assembly, etc.

This part is fixed, cannot be programmed

  • Primitive assembly
    • Vertex data is collected into complete primitives
    • Necessary for clipping and back-face culling
  • Clipping
  • Perspective division
    • To normalized device coordinate (NDC) space
  • Viewport transformation
    • To windows space
    • Include depth range scaling
  • Back-face culling

Rasterization

  • If geometric primitive is not clipped out, the appropriate pixels in the frame buffer must be assigned colors
  • Rasterizer produces a set of framgements for each primitive
    • Fragments are “potential pixels”, they have pixel/fragment locations (in window space) and have color and depth attributes (and others)

Fragment Shading

  • Executed per fragment
  • Each generated fragment is processed to determine the color of the corresponding pixel in the framebuffer

Per-Fragment Operations

After fragment shading, each resulting fragment is submitted to a set of simple operations before reaching the framebuffer

Framebuffer

A framebuffer (frame buffer or framestore) is a portion of random-access memory (RAM) containing a bitmap that drives a video display. It is a memory buffer containing a complete frame of data.

Modern OpenGL

OpenGL 4.5

Some OpenGL Libraries

GLUT (OpenGL Utility Toolkit)

  • Too Old

FreeGLUT

  • Based on GLUT API
  • Open source
  • Many tutorials and examples out there use GLUT/freeGLUT
  • Fully compatible with GLUT
  • More bugs sometimes

http://freeglut.sourceforge.net/

GLEW (OpenGL Extension Wrangler)

  • Cross platform
  • Open source
  • C/C++ extension loading library

http://glew.sourceforge.net/

GLM (OpenGL Mathematics)

  • A header only C++ mathematics library for graphics software based on the OpenGL Shading Language (GLSL) specifications

https://glm.g-truc.net/0.9.9/index.html

GLFW

  • Open source
  • Multi platform
  • Provides a simple API for creating windows, contexts and surface, receiving input and events.
  • Similar to GLUT/FreeGLUT

https://www.glfw.org/

Modern OpenGL

User can design their own shaders in modern OpenGL.