COMP 175 | COMPUTER GRAPHICS Remco Chang1/XX13 – GLSL Lecture 13: OpenGL Shading Language (GLSL) COMP 175: Computer Graphics April 12, 2016

COMP 175 | COMPUTER GRAPHICS Remco Chang2/XX13 – GLSL  Last week, we discussed the many of the new “tricks” in Graphics require low-level access to the Graphics pipeline  For example, using textures, which is a pain in regular OpenGL. Motivation

COMP 175 | COMPUTER GRAPHICS Remco Chang3/XX13 – GLSL Graphics History  Software Rendering  Old-fashioned way (Use ray casting)  Fixed-Function  Immediate Mode (What we have used)  Programmable Pipeline (~2001)  GL Shading Language (What we will learn)  CUDA/OpenCL (GPGPU) (~2008)  General Purpose GPU Programming

COMP 175 | COMPUTER GRAPHICS Remco Chang4/XX13 – GLSL Ray Casting (Software Rendering)  Wolfenstein  Quake 1

COMP 175 | COMPUTER GRAPHICS Remco Chang5/XX13 – GLSL Fixed-Function  Quake 3  Half-Life

COMP 175 | COMPUTER GRAPHICS Remco Chang6/XX13 – GLSL Programmable Pipeline (Shaders)  Doom 3  Far Cry

COMP 175 | COMPUTER GRAPHICS Remco Chang7/XX13 – GLSL GPGPU  General Purpose Graphics Processing Unit  Utilize graphics card for computation  Do work other than graphics

COMP 175 | COMPUTER GRAPHICS Remco Chang8/XX13 – GLSL Old Fixed-Function

COMP 175 | COMPUTER GRAPHICS Remco Chang9/XX13 – GLSL Programmable Pipeline

COMP 175 | COMPUTER GRAPHICS Remco Chang10/XX13 – GLSL Accessing Programmable Pipeline Introducing Shaders! 4/15/

COMP 175 | COMPUTER GRAPHICS Remco Chang11/XX13 – GLSL  CPU: Typical C++ code  GPU: OpenGL Shading Language (GLSL)  CPU passes data to GPU  Some processing happens on the CPU:  Get mouse movement  Load and parse data from disk  Some processing happens on the GPU:  Transform point from Object to World space  Solve lighting equation  Render CPU + GPU

COMP 175 | COMPUTER GRAPHICS Remco Chang12/XX13 – GLSL  Most common:  Vertex  Fragment (Pixel)  Newer:  Geometry  Tessellation  Compute Types of Shaders

COMP 175 | COMPUTER GRAPHICS Remco Chang13/XX13 – GLSL  OpenGL Shading Language (GLSL)  Syntax  Sequence and processes  Vertex Shader  Pixel Shader  Communication between CPU and GPU  What type of information can be passed  How to pass information  Note that you also need to know how to load a shader program, but that’s “magic incantation” that (mostly) stays the same every time. Two Things to Learn:

COMP 175 | COMPUTER GRAPHICS Remco Chang14/XX13 – GLSL

COMP 175 | COMPUTER GRAPHICS Remco Chang15/XX13 – GLSL Interfacing with the GPU  Modern OpenGL  Mobile/Web Programming  Direct3D  Compute Languages  Stream, OpenCL, CUDA  Future

COMP 175 | COMPUTER GRAPHICS Remco Chang16/XX13 – GLSL Client/Server Architecture  Think of like a network  Client = the CPU  Server = the GPU  The less they talk, the better  Less waiting for memory to transfer  Bandwidth is almost always the bottleneck  Send data over once, and have it ready to go

COMP 175 | COMPUTER GRAPHICS Remco Chang17/XX13 – GLSL Optimizations Available  Vertex Array  Display Lists  Vertex Buffer Objects  Pixel Buffers  Frame Buffer Objects Michael Shah

COMP 175 | COMPUTER GRAPHICS Remco Chang18/XX13 – GLSL Immediate Mode  Every ‘gl’ command is being sent to the GPU every iteration.  Very inefficient  Think of it like having an interpreter versus a compiler for C++ Michael Shah

COMP 175 | COMPUTER GRAPHICS Remco Chang19/XX13 – GLSL Vertex Array  No more glBegin/glEnd  Store Vertices, indices, normals, colors, texture coordinates in an array  Minimizes OpenGL calls on Client (CPU)  Data still being passed from Client to Server every frame  A little better because it’s all at once  Stylistically, much cleaner code as well Michael Shah

COMP 175 | COMPUTER GRAPHICS Remco Chang20/XX13 – GLSL  Compiled geometry  Send it to the Server(GPU) once, and it is stored in memory on Server  Geometry cannot be updated, without deleting display list. someGeometryDisplayList = glGenLists(1); glNewList(someGeometryDisplayList,GL_COMPILE); drawShape(); glEndList(); Display List 4/22/2014 Michael Shah 20

COMP 175 | COMPUTER GRAPHICS Remco Chang21/XX13 – GLSL Vertex Buffer Object (VBO)  Improves upon Vertex Array  We can store data on the Server (GPU)  Just like display lists!  We get a pointer into the Server (GPU) so that we can update it!  As good as display lists!  Because we have a pointer to the data, multiple clients can access data.  Multiple instances of a program can access data 4/22/2014 Michael Shah 21

COMP 175 | COMPUTER GRAPHICS Remco Chang22/XX13 – GLSL Modifiers to Variables Uniform/Varying/Attribute  Uniform – Read only data passed into vertex/fragment shaders  Attributes – Input value which change every vertex.  Read only – Used only in vertex shader  Depending on GLSL version:  GLSL <3.0: Varying – Pass data from vertex to fragment shader.  GLSL >=3.0: in / out – in is the variable being passed in, out is the variable being passed out  Read-only in fragment shader.  Read/Write in Vertex Shader

COMP 175 | COMPUTER GRAPHICS Remco Chang23/XX13 – GLSL OpenGL Shading Language

COMP 175 | COMPUTER GRAPHICS Remco Chang24/XX13 – GLSL GLSL  C-Like Language  Made for GPU Architecture  Because GPU’s are different than CPU’s  Still Cross Platform  Debugging – Still as difficult  Domain Specific Language  Compiled at runtime

COMP 175 | COMPUTER GRAPHICS Remco Chang25/XX13 – GLSL GLSL Primitives  float, int, bool Example: float f = 10.0; or float f = float(10); (Casting not allowed, choose your type wisely!)

COMP 175 | COMPUTER GRAPHICS Remco Chang26/XX13 – GLSL GLSL Types  Vector: vec2, vec3, vec4  Overloaded to take in each type  Example: vec4 temp= vec4(1.0, 1.0, 1.0, 1.0)  Matrix: mat2, mat3, mat4  Example: glModelViewMatrix is a mat4 type  Access first column with: mat[0]  Access second column with: mat[1]  Example: mat[1] = vec3(1.0, 1.0, 1.0);  Access individual element: mat[2][1];

COMP 175 | COMPUTER GRAPHICS Remco Chang27/XX13 – GLSL Some more examples  Pass in vec3 into a vec4 vec3 color = vec3(1.0,0.5,0.25) vec4 temp = vec4(color, 1.0)  Get components of vector  color.x = 1.0; or color[0] = 1.0  color.y = 1.0; or color[1] = 1.0;

COMP 175 | COMPUTER GRAPHICS Remco Chang28/XX13 – GLSL Swizzling [1][1]  Swizzling is the ability to rearrange a vectors components  vec2 pos = temp.xy; // retrieve x and y component, or any of xyzw  vec2 pos = temp.yz;  vec4 = color.agbr; // opposite of rgba

COMP 175 | COMPUTER GRAPHICS Remco Chang29/XX13 – GLSL  Note that some of these default keywords might not be there depending on GLSL version number (for example: gl_ModelViewMatrix isn’t there any more) More GLSL Keywords [1][2]12

COMP 175 | COMPUTER GRAPHICS Remco Chang30/XX13 – GLSL Write a Simple Shader Basic Vertex and Fragment Shader

COMP 175 | COMPUTER GRAPHICS Remco Chang31/XX13 – GLSL Writing a Shader  Writing a shader, compiling a shader, and loading a shader  Compile at runtime  So we do not need to recompile entire source, if we only modify shader.

COMP 175 | COMPUTER GRAPHICS Remco Chang32/XX13 – GLSL

COMP 175 | COMPUTER GRAPHICS Remco Chang33/XX13 – GLSL Simple Vertex Shader

COMP 175 | COMPUTER GRAPHICS Remco Chang34/XX13 – GLSL Simple Fragment Shader

COMP 175 | COMPUTER GRAPHICS Remco Chang35/XX13 – GLSL The cpp file

COMP 175 | COMPUTER GRAPHICS Remco Chang36/XX13 – GLSL Drawing with immediate mode for now

COMP 175 | COMPUTER GRAPHICS Remco Chang37/XX13 – GLSL Final Image