Author: Romain Vergne (website)
Please cite my name and add a link to my web page if you use this course

Image synthesis and OpenGL: exercices 03

Setup

We will use Linux and the following libraries:

OpenGL: Open Graphics Library (online spec, pdf spec)
GLU: OpenGL Utility Library
GLEW: OpenGL Extension Wrangler Library
GLM: OpenGL Mathematics library
QT: the window manager

Installing sources. In a terminal, do:

Download the sources at http://romain.vergne.free.fr/teaching/IS/data03/TP03.tgz
If needed, edit the file main.pro to change paths
To compile: qmake && make
To run: ./tp03 models/file.off
To edit: use either your prefered text editor or qtcreator

Towards the OpenGL 4 pipeline

The goal of these exercises is to familiarize yourself with OpenGL vertex arrays and shaders (that's a lot!). You should obtain something like this:

Exercice 1: real-time coding (with the prof.)

Shader creation & initialization
VAO creation & initialization
Using another attribute (normals)

CPU transfer
rasterization
display

Sending uniform variables

CPU transfer
using the variable inside the shader

Exercice 2: get familiarized with the code

Have a look at the OpenGL documentation of the following functions:

glClear
glGenBuffers / glDeleteBuffers
glGenVertexArrays / glDeleteVertexArrays
glBindVertexArray
glBindBuffer
glBufferData
glVertexAttribPointer
glEnableVertexAttribArray / glDisableVertexAttribArray
glDrawElements / glDrawArrays

glCreateProgram
glUseProgram
glCreateShader
glShaderSource
glCompileShader
glLinkProgram
glUniform

Exercice 3: Play with shaders

Each time you change something in the shader file, you can test directly wihout having to re-execute the program since shaders can be compiled at runtime.
Simply press the "r" button (see viewer.cpp): it will call shader->reload and re-compile everything.
Your may also visualize the mesh in wireframe by pressing the "w" key.

Do not forget to read the GLSL specification for creating and modifying shaders.

apply some simple transformations (scale/translate/etc) to the mesh vertices. Observe what happens.
send a animated uniform variable to the shader (for instance the scalar _var available in viewer.h)
animate the transformations
and / or use the variable to modify the rendering colors
try different GLSL functions on the output color, for instance

step
smoothstep
mix
etc (see the built-in functions in the GLSL documentation)

Try to modulate your rendering according to any kind of 3D function (how to obtain a checkerboard effect for instance)?
What does the function discard do? Try to use it somewhere.

PREVIOUS: 03 - PIPELINES

NEXT: 04 - LIGHTING