Computer Graphics  
Lecture 05 Shaders  
Edirlei Soares de Lima  
<edirlei.lima@universidadeeuropeia.pt>  
Graphics Pipeline  
Shaders  
Shaders are pieces of code written in a shading language.  
They describe how to process data in the graphics pipeline.  
The term “shader” was proposed by Cook [1984] to describe  
small programs written by the user as part of the modeling  
process to determine the color of objects.  
Types of shaders:  
Vertex shaders;  
Fragment shaders;  
Geometry shaders;  
Tessellation shaders;  
Shading Languages  
GLSL Standardized shading language used by OpenGL.  
HLSL C-style shader language for Direct3D.  
Cg Shading language developed by NVIDIA for easy and  
efficient production pipeline integration.  
RSL Shader language used by the Pixar RenderMan software  
(offline rendering).  
OSL Shading language developed by Sony and also used in  
Blender.  
Shaders in Unity  
The rendering process in Unity is entirely based on shaders:  
Shaders in Unity  
The rendering process in Unity is entirely based on shaders:  
with standard shader  
without shader  
Shading language: ShaderLab (HLSL + Cg).  
Shaders in Unity  
Main Unity Shader Types:  
Unlit Vertex, Frangment, Geometry, and Tessellation Shaders;  
Surface Code generation approach that makes it easier to write  
lighting shaders;  
Shaders in Unity  
Create a new shader: Create->Shaders->Unlit  
Shader "Custom/MyShader"{  
Properties{  
}
SubShader{  
Pass{  
}
}
}
Vertex and Fragment Shaders  
The Vertex Shader is responsible for  
processing individual vertices of a mesh.  
The Fragment Shader is responsible for  
processing (usually coloring) the  
fragments (generated by Rasterization)  
that lie inside the mesh's triangles.  
Vertex and Fragment Shaders  
Shader "Custom/MyShader"{  
Properties{  
}
SubShader{  
Pass{  
Definition of the functions that will  
be vertex and fragment programs.  
CGPROGRAM  
#
#
pragma vertex MyVertexProgram  
pragma fragment MyFragmentProgram  
Includes some essential  
functionalities to write shaders.  
#include "UnityCG.cginc"  
void MyVertexProgram(){  
}
void MyFragmentProgram(){  
}
ENDCG  
Implementation of the vertex and  
fragment programs/functions.  
}
}
Note: this shader do not produce any  
results (the objects using it will disappear).  
}
Vertex and Fragment Shaders  
To render something, the vertex program has to return the  
final coordinates of an input vertex, which is sent to the  
fragment program as input. The fragment program must  
return the final color of the fragment.  
float4 MyVertexProgram(float4 position : POSITION) : SV_POSITION  
{
Transforms the vertex  
from object space to  
camera space.  
return UnityObjectToClipPos(position);  
}
float4 MyFragmentProgram(float4 position:SV_POSITION):SV_TARGET  
{
return float4(0, 0, 0, 1);  
}
Unity Shader Compilation  
Unity compiles the shader code to a  
different shader language depending on  
the target platform.  
Different APIs and platforms require  
different shader languages.  
Windows Direct3D: HLSL  
MacOS OpenGL: GLSL  
Android OpenGL ES: GLSL ES  
Shader Properties  
Shader properties are declared in a separate block of code.  
Shader "Custom/MyShader"{  
Properties{  
_
Color("Color", Color) = (1, 1, 1, 1)  
SubShader{  
..  
}
.
}
}
Shader Properties  
Shader properties are declared in a separate block of code.  
CGPROGRAM  
...  
float4 _Color;  
float4 MyVertexProgram(float4 position:POSITION):SV_POSITION{  
return UnityObjectToClipPos(position);  
}
float4 MyFragmentProgram(float4 position:SV_POSITION):SV_TARGET{  
return _Color;  
}
ENDCG  
Sending More Information From  
Vertex To Fragment  
We can define a structure to send more information about  
each vertex to its respective fragment program.  
...  
struct VertexToFragment {  
float4 position : SV_POSITION;  
float3 localPosition : TEXCOORD0;  
};  
VertexToFragment MyVertexProgram(float4 position : POSITION){  
VertexToFragment v2f;  
v2f.localPosition = position.xyz;  
v2f.position = UnityObjectToClipPos(position);  
return v2f;  
Makes a copy of  
the local position  
of the vertex.  
}
float4 MyFragmentProgram(VertexToFragment v2f) : SV_TARGET{  
return float4(v2f.localPosition + 0.5, 1) * _Color;  
}
Uses the local position of the  
vertex to compute its color.  
...  
Texturing  
Texturing consists of projecting an image onto the triangles of  
a mesh.  
Texture coordinates are used to control the projection. These  
coordinates are 2D pairs that cover the entire image in a one-  
unit square area.  
The horizontal coordinate is known as U and the vertical coordinate as  
V (UV coordinates).  
Texturing  
Texturing  
Unity's default meshes have UV coordinates and the vertex  
program can access them.  
struct VertexData {  
float4 position : POSITION;  
float2 uv : TEXCOORD0;  
};  
struct VertexToFragment {  
float4 position : SV_POSITION;  
float2 uv : TEXCOORD0;  
};  
VertexToFragment MyVertexProgram(VertexData vert){  
VertexToFragment v2f;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv;  
return v2f;  
}
Texturing  
We need to add another shader property for the texture and  
define another variable in the shader program to access the  
texture (type sampler2D).  
Properties  
{
_
_
Color("Color", Color) = (1, 1, 1, 1)  
MainTex("Texture", 2D) = "white" {}  
}
CGPROGRAM  
..  
.
float4 _Color;  
sampler2D _MainTex;  
...  
Texturing  
Sampling the texture with the UV coordinates is done in the  
fragment program, by using the tex2D function.  
...  
float4 MyFragmentProgram(VertexToFragment v2f) : SV_TARGET{  
return tex2D(_MainTex, v2f.uv) * _Color;  
}
...  
Texturing Tiling and Offset  
When we added a texture to our shader,  
the material inspector also added tiling  
and offset controls. These values can be  
accessed and used by the shader.  
sampler2D _MainTex;  
float4 _MainTex_ST;  
The same name as the  
texture, plus the _ST suffix.  
...  
VertexToFragment MyVertexProgram(VertexData vert){  
VertexToFragment v2f;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
return v2f;  
}
Combining Textures  
We can also use shaders to combine textures and add more  
details the surfaces of the objects.  
Tiling 1x1  
Texture  
Tiling 10x10  
Combining Texture  
We can also use shaders to combine textures and add more  
details the surfaces of the objects.  
...  
float4 MyFragmentProgram(VertexToFragment v2f) : SV_TARGET{  
float4 color = tex2D(_MainTex, v2f.uv) * _Color;  
color *= tex2D(_MainTex, v2f.uv * 10);  
return color;  
}
...  
Combining Textures  
When you multiply two textures together, the result will be  
darker. To brighten the original texture, we can multiply the  
color by 2.  
..  
.
float4 MyFragmentProgram(VertexToFragment v2f) : SV_TARGET{  
float4 color = tex2D(_MainTex, v2f.uv) * _Color;  
color *= tex2D(_MainTex, v2f.uv * 10) * 2;  
return color;  
}
...  
Combining Textures  
A better solution is to use a special detail texture, which is  
centered around gray.  
Tiling 1x1  
Texture  
Detail Texture  
Tiling 10x10  
Combining Textures  
To use a second detail texture, we have to add a new texture  
property to the shader.  
Properties  
{
_Color("Color", Color) = (1, 1, 1, 1)  
_MainTex("Texture", 2D) = "white" {}  
_DetailTex("Detail Texture", 2D) = "gray" {}  
}
sampler2D _MainTex, _DetailTex;  
float4 _MainTex_ST, _DetailTex_ST;  
struct VertexToFragment {  
float4 position : SV_POSITION;  
float2 uv : TEXCOORD0;  
float2 uvDetail : TEXCOORD1;  
};  
Combining Textures  
To use a second detail texture, we have to add a new texture  
property to the shader.  
VertexToFragment MyVertexProgram(VertexData vert){  
VertexToFragment v2f;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
v2f.uvDetail = vert.uv * _DetailTex_ST.xy + _DetailTex_ST.zw;  
return v2f;  
}
float4 MyFragmentProgram(VertexToFragment v2f):SV_TARGET{  
float4 color = tex2D(_MainTex, v2f.uv) * _Color;  
color *= tex2D(_DetailTex, v2f.uvDetail) * 2;  
return color;  
}
Combining Textures  
To use a second detail texture, we have to add a new texture  
property to the shader.  
VertexToFragment MyVertexProgram(VertexData vert){  
VertexToFragment v2f;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
v2f.uvDetail = vert.uv * _DetailTex_ST.xy + _DetailTex_ST.zw;  
return v2f;  
}
float4 MyFragmentProgram(VertexToFragment v2f):SV_TARGET{  
float4 color = tex2D(_MainTex, v2f.uv) * _Color;  
color *= tex2D(_DetailTex, v2f.uvDetail) *  
unity_ColorSpaceDouble;  
return color;  
}
Combining Textures  
Same texture multiplied  
Using a separated gray detail texture  
Same texture multiplied and brighter  
Level of Detail with Mipmaps  
Mipmaps are pre-calculated sequences  
of images with a progressively lower  
resolution representation of the same  
image.  
They are intended to increase rendering  
speed and reduce aliasing artifacts.  
Level of Detail with Mipmaps  
Without Mipmaps  
With Mipmaps  
Using a Noise Texture to “Dissolve” an Object  
We need a new texture and a float property:  
Properties  
{
_
_
_
_
Color("Color", Color) = (1, 1, 1, 1)  
MainTex("Texture", 2D) = "white" {}  
DissolveTexture ("Dissolve Texture", 2D) = "white" {}  
DissolveCutoff ("Dissolve Cutoff", Range(0, 1)) = 1  
}
sampler2D _MainTex, _DissolveTexture;  
float4 _MainTex_ST;  
float _DissolveCutoff;  
struct VertexToFragment {  
float4 position : SV_POSITION;  
float2 uv : TEXCOORD0;  
};  
Using a Noise Texture to “Dissolve” an Object  
The clip function checks if the given value is less than 0. If it is,  
then it discards the pixel and draw nothing. If it isn’t it keeps  
the pixel and continue as normal.  
VertexToFragment MyVertexProgram(VertexData vert) {  
VertexToFragment v2f;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
return v2f;  
}
float4 MyFragmentProgram(VertexToFragment v2f) : SV_TARGET{  
float4 textureColor = tex2D(_MainTex, v2f.uv) * _Color;  
float4 dissolveColour = tex2D(_DissolveTexture, v2f.uv);  
clip(dissolveColour.rgb - _DissolveCutoff);  
return texturecolor;  
}
Manipulating Vertices  
The Vertex Shader allows us to manipulate each vertex  
individually.  
Simple example:  
Moves all  
vertices to  
the right.  
VertexToFragment MyVertexProgram(VertexData vert){  
VertexToFragment v2f;  
vert.position.x += 1;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
return v2f;  
}
Manipulating Vertices  
Unity provides some handful of built-in variables that allow us  
to access some important values in a shader. One of these  
variables is the time:  
_Time : float4 - running time as float4 (t/20, t, t*2, t*3)  
VertexToFragment MyVertexProgram(VertexData vert){  
VertexToFragment v2f;  
vert.position.x += sin((_Time.y*3)+(vert.position.y*5))*0.1;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
return v2f;  
}
Exercise 1  
1
) The code that implements the deformation in the object is  
using some constants (3, 5, 0.1) to determine how the object  
is deformed. Change the shader code to use parameterized  
properties instead of constant values.  
.
..  
vert.position.x += sin((_Time.y * 3)+(vert.position.y * 5)) * 0.1;  
..  
.
Extruding Objects  
Extrusion push the faces of the objects in or out.  
Properties{  
...  
_ExtrudeAmount("Extrude Amount", float) = 0  
}
...  
float _ExtrudeAmount;  
struct VertexData {  
...  
float3 normal : NORMAL;  
};  
VertexToFragment MyVertexProgram(VertexData vert) {  
VertexToFragment v2f;  
vert.position.xyz += vert.normal.xyz * _ExtrudeAmount;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
return v2f;  
}
Accessing Shaders Properties by Script  
public class ExtrusionAnimator : MonoBehaviour  
{
private Renderer render;  
void Start()  
{
render = GetComponent<Renderer>();  
}
void Update ()  
{
render.material.SetFloat("_ExtrudeAmount", Time.time);  
}
}
Manipulating Vertices  
We can also use the information of an image to manipulate  
the vertices an object.  
Properties  
{
_
_
_
Color("Color", Color) = (1, 1, 1, 1)  
MainTex("Texture", 2D) = "white" {}  
DeformTex("Detail Texture", 2D) = "gray" {}  
Lookup the color values  
of a 2D texture.  
}
VertexToFragment MyVertexProgram(VertexData vert) {  
VertexToFragment v2f;  
float4 deformColor = tex2Dlod(_DeformTex,float4(vert.uv.xy,0,0));  
vert.position.y += deformColor.r;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv * _MainTex_ST.xy + _MainTex_ST.zw;  
return v2f;  
}
Manipulating Vertices  
We can also use the information of an image to manipulate  
the vertices an object.  
Flat plane  
Texture  
Manipulated plane  
Deformation Texture  
Post-Processing Shaders Image Effects  
After a virtual camera has rendered an image, it is often  
useful to apply some image post-processing to the image.  
Artistic reasons and technical reasons.  
A post-processing shader needs a shader and script file.  
[RequireComponent(typeof(Camera))]  
[ExecuteInEditMode]  
public class Test : MonoBehaviour {  
public Material material;  
void OnRenderImage(RenderTexture source,  
RenderTexture destination){  
Graphics.Blit(source, destination, material);  
}
}
Post-Processing Shaders Image Effects  
Shader "Image Effect/InvertColor"{  
Properties{  
_MainTex ("Source", 2D) = "white" {}  
}
SubShader{  
Cull Off  
ZWrite Off  
ZTest Always  
Pass{  
CGPROGRAM  
#
#
#
pragma vertex MyVertexProgram  
pragma fragment MyFragmentProgram  
include "UnityCG.cginc"  
sampler2D _MainTex;  
float4 _MainTex_ST;  
struct VertexData{  
float4 position : POSITION;  
float2 uv : TEXCOORD0;  
};  
struct VertexToFragment{  
float4 position : POSITION;  
float2 uv : TEXCOORD0;  
};  
VertexToFragment MyVertexProgram(VertexData vert){  
VertexToFragment v2f;  
v2f.position = UnityObjectToClipPos(vert.position);  
v2f.uv = vert.uv;  
return v2f;  
}
float4 MyFragmentProgram(VertexToFragment v2f) : SV_TARGET{  
float4 color = tex2D(_MainTex, v2f.uv);  
return 1 - color;  
}
ENDCG  
}
}
}
Exercise 2  
2
) Implement image effect shaders for the following effects:  
a) Add a red tone to the rendered  
image;  
b) Transform the rendered image  
into a gray scale image;  
c) Add a blur effect to the rendered  
image;  
Further Reading  
Hughes, J. F., et al. (2013). Computer Graphics: Principles and Practice  
(
0
3rd ed.). Upper Saddle River, NJ: Addison-Wesley Professional. ISBN: 978-  
-321-39952-6.  
Chapter 33: Shaders  
Web:  
http://catlikecoding.com/unity/tutorials/rendering/part-2/  
http://catlikecoding.com/unity/tutorials/rendering/part-3/