Shader Programming
BY TIGRAN GASPARIAN
Who am I?
Name: Tigran Gasparian
Age: 22
Master student Game and Media Technology
Working on a game for almost two years already
◦ The Flock – multiplayer horror game
◦ Like us on Facebook!
◦ Doing a lot of graphics programming in Unity
Table of contents
Introduction and motivation
Graphics pipeline
Vertex shader intro
Pixel shader intro
Writing shaders in XNA
Tips & Tricks
What are shaders?
Programs that run on the graphics card
◦ Somewhat limited compared to languages like C#
◦ Because of these limitations, very good at certain tasks
◦ Perform some of the computations necessary for graphics
We’ll cover pixel and vertex shaders
◦ Geometry, Tessellation and Compute shaders not covered here.
Written in some shading language
◦ HLSL, GLSL, CG, PSSL, MSL, etc.
◦ We’re going to use HLSL – High Level Shading Language
Node-based editor
What are shaders?
Why learn to write shaders?
Game engines come with lots of built-in shaders
Why learn to write shaders?
Create a unique look and feel for your game
◦ Want something never done before? Do it yourself!
Implement state of the art techniques
◦ The latest and greatest techniques don’t have standard implementations yet.
Unlock the infinite powers of the GPU!
◦ Well, not infinite, but it’s certainly powerful.
◦ 14x speedup according to Intel
◦ 300x speedup according to NVIDIA
◦ Depends on the application.
Why learn to write shaders?
It helps you pass the second practicum.
The Graphics Pipeline
What is the graphics pipeline?
◦ A sequence of actions that is performed to render a 2D image
from a 3D scene
We’ll cover the following stages:
◦ Vertex Shader
◦ Rasterizer
◦ Can’t be programmed, but it’s an important stage
◦ Pixel Shader
Will be covered in-depth in the next lecture.
The Graphics Pipeline
Vertex data + resources + graphics card = image!
What is vertex data?
◦ Mostly triangles
What kind of resources?
◦ Textures
◦ Global variables
◦ Like the light color
◦ Lots of other stuff we won’t cover.
We first set the resources, then we push the vertices to the
graphics card
The Vertex Shader
Perform some computations per vertex.
◦ Can move the positions of vertices.
◦ Usually transforms vertices
◦ Using the World, View and Projection matrices
The Vertex Shader
Perform some computations per vertex.
◦ Can move the positions of vertices.
◦ Usually transforms vertices
◦ Using the World, View and Projection matrices
◦ Other deformations
The Rasterizer
Turns triangles into pixels!
Interpolates vertex data
◦ More about this later
The Pixel Shader
Perform computations per pixel
◦ More accurate than per-vertex computations
◦ Can’t change the shape of the geometry
◦ Vertex shaders can!
Common uses
◦ Texture mapping
◦ We need to sample the texture for every pixel
◦ Per pixel lighting
The Vertex Shader – In-Depth
What’s a vertex shader?
◦ Just a function called for every vertex
Input: Vertex data
◦ A struct containing vertex information
◦ Let’s call it: VertexShaderInput
Output: A struct
◦ Can contain anything
◦ Let’s call it: VertexShaderOutput
Observation: Vertex shader doesn’t know about triangles
The Vertex Shader – VertexShaderInput
struct VertexShaderInput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
float2 TextureCoordinate : TEXCOORD0;
float SomeCustomData : TEXCOORD1;
};
The data sent from the CPU to the GPU
HLSL code
Looks like C
◦ New data types
◦ Input semantics
The Vertex Shader – VertexShaderOutput
struct VertexShaderOutput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
float3 VertexPosition : TEXCOORD0;
};
Must have member with POSITION0 semantic
◦ Contains vertex position transformed to normalized device coordinates
Sidetrack #1 - Input semantics
Required for interaction with C# code
◦ More on this later
Lots of remnants from the fixed function pipeline era.
Lots of semantics
◦ POSITION[n]
◦ TEXCOORD[n] (e.g. TEXCOORD0, TEXCOORD1, etc..)
◦ Use this for all custom data
◦ COLOR[n]
◦ Clamped between 0 and 1
◦ NORMAL[n]
◦ Many more…
Sidetrack #2 - HLSL Data types
HLSL has some specialized data types
◦ float – nothing special
◦ float2 – 2D vector
◦ float3 – 3D vector
◦ float4 – 4D vector
◦ float4x4 – 4x4 float matrix
◦ float2x3 – 2x3 float matrix
◦ Same thing with
◦ half – 16 bit floats
◦ fixed – 8 bit floats
◦ int – 32 bit integer
◦ etc.
Sidetrack #3 - HLSL Data types
float3 position = float3(0, 0, 0);
float3 direction = float3(1, 2, 1.2f);
float someValue = 5;
position += direction * someValue;
float yDirection = direction.y;
float2 xyDirection = direction.xy;
Works mostly like you’d expect it to.
We’ll cover more HLSL later on
The Graphics Pipeline
We just covered the Vertex Shader
Output:
struct VertexShaderOutput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
float3 VertexPosition : TEXCOORD0;
};
The Graphics Pipeline
We just covered the Vertex Shader
Output:
struct VertexShaderOutput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
float3 VertexPosition : TEXCOORD0;
};
Input for Rasterizer
The Rasterizer
Converts triangles into pixels
◦ Or: Rasterizes triangles
The Rasterizer
Converts triangles into pixels
◦ Or: Rasterizes triangles
Interpolates values between vertices
◦ For example the colors
struct VertexShaderOutput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
float3 VertexPosition : TEXCOORD0;
};
The Rasterizer – Linear Interpolation
Values in the vertex structures are linearly interpolated
float LinearInterpolate(float a, float b, float t)
{
return (1 - t)*a + t*b;
}
Weighted average
Can also be done with vectors and colors
◦ Interpolating vectors does not preserve length
◦ Renormalize your normals after interpolation!
The Rasterizer – Interpolating vectors
Can also be done with vectors and colors
◦ Interpolating vectors does not preserve length
◦ Renormalize your normals after interpolation!
Notice what happens when we interpolate between the blue and red vectors
The Graphics Pipeline
After the rasterizer stage, we end up with pixels.
struct VertexShaderOutput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
float3 VertexPosition : TEXCOORD0;
};
The Graphics Pipeline
After the rasterizer stage, we end up with pixels.
struct VertexShaderOutput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
float3 VertexPosition : TEXCOORD0;
};
For every pixel, we get a VertexShaderOutput struct
◦ With POSITION0 field removed
The Pixel Shader – In-Depth
What’s a pixel shader?
◦ Just a function called for every pixel
Input: Interpolated Vertex Shader Output
◦ We reuse the struct VertexShaderOutput
◦ POSITION0 field “eaten” by the rasterizer
Output: One or more colors (or depth)
◦ We can put this in a struct
◦ Or just output a float4
The Pixel Shader – PixelShaderOutput
struct PixelShaderOutput
{
float4 color : COLOR0;
};
COLOR0 semantic is mandatory
And that’s it!
Simple example – Vertex Color shader
Walkthrough for a simple shader
Vertex shader:
◦ Transform cube with World, View and Projection matrix
◦ Pass vertex colors to rasterizer
Pixel shader
◦ Output interpolated vertex colors
Simple example – Vertex Color shader
struct VertexShaderInput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
};
struct VertexShaderOutput
{
float4 Position : POSITION0;
float4 Color : COLOR0;
};
float4x4 World;
float4x4 View;
float4x4 Projection;
Simple example – Vertex Color shader
VertexShaderOutput VertexShaderFunction(VertexShaderInput input)
{
VertexShaderOutput output;
float4 worldPosition = mul(input.Position, World);
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);
output.Color = input.Color;
return output;
}
Simple example – Vertex Color shader
struct PixelShaderOutput
{
float4 color : COLOR0;
};
PixelShaderOutput PixelShaderFunction(VertexShaderOutput input)
{
PixelShaderOutput output;
output.color = input.Color;
return output;
}
Simple example – Vertex Color shader
float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
{
return input.Color;
}
Simple example – Vertex Color shader
Tell the compiler which functions are the vertex shader and the pixel shader
Technique
◦ A shader file consists of one or more techniques (e.g. effect)
Pass
◦ Every technique consists of one or more passes
◦ Every pass consists of a vertex shader and a pixel shader
Simple example – Vertex Color shader
technique VertexColorsTechnique
{
pass FirstPass
{
VertexShader = compile vs_2_0 VertexShaderFunction();
PixelShader = compile ps_2_0 PixelShaderFunction();
}
}
We choose a vertex shader and pixel shader profile
◦ Lower profile – 2_0 – less capabilities, supports older graphics cards
◦ Higher profile – 3_0 – more capabilities, only supports more recent graphics cards
Simple example – Vertex Color shader
That’s it!
◦ Not that much code!
Simple example – Vertex Color shader
float4x4 World; VertexShaderOutput VertexShaderFunction(VertexShaderInput input)
float4x4 View; {
float4x4 Projection; VertexShaderOutput output;
struct VertexShaderInput float4 worldPosition = mul(input.Position, World);
{ float4 viewPosition = mul(worldPosition, View);
float4 Position : POSITION0; output.Position = mul(viewPosition, Projection);
float4 Color : COLOR0; output.Color = input.Color;
};
return output;
struct VertexShaderOutput }
{
float4 Position : POSITION0; float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
float4 Color : COLOR0; {
}; return input.Color;
}
technique VertexColorsTechnique
{
pass FirstPass
{
VertexShader = compile vs_2_0 VertexShaderFunction();
PixelShader = compile ps_2_0 PixelShaderFunction();
}
}
Using shaders in XNA
Vertex declarations
Loading shaders
Setting global variables
Rendering
Vertex Declarations
You’ve probably used this in P1
private VertexPositionColor[] vertices;
Later in P1, you define your own vertex types (see Section 7.2 of P1)
private VertexPositionColorNormal[] vertices;
Vertex Declarations
In the vertex declaration, we see this:
public static VertexElement[] VertexElements =
{
new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0),
new VertexElement(sizeof (float)*3, VertexElementFormat.Color, VertexElementUsage.Color, 0),
new VertexElement(sizeof (float)*3 + 4, VertexElementFormat.Vector3, VertexElementUsage.Normal, 0),
};
Relates to the following shader code:
struct VertexShaderInput
{
float3 Position : POSITION0;
float4 Color : COLOR0;
float3 Normal : NORMAL0;
};
Vertex Declarations
In the vertex declaration, we see this:
public static VertexElement[] VertexElements =
{
new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0),
new VertexElement(sizeof (float)*3, VertexElementFormat.Color, VertexElementUsage.Color, 0),
new VertexElement(sizeof (float)*3 + 4, VertexElementFormat.Vector3, VertexElementUsage.Normal, 0),
};
Relates to the following shader code:
struct VertexShaderInput
{
float3 Position : POSITION0;
float4 Color : COLOR0;
float3 Normal : NORMAL0;
};
Vertex Declarations
In the vertex declaration, we see this:
public static VertexElement[] VertexElements =
{
new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0),
new VertexElement(sizeof (float)*3, VertexElementFormat.Color, VertexElementUsage.Color, 0),
new VertexElement(sizeof (float)*3 + 4, VertexElementFormat.Vector3, VertexElementUsage.Normal, 0),
};
Relates to the following shader code:
struct VertexShaderInput
{
float3 Position : POSITION0;
float4 Color : COLOR0;
float3 Normal : NORMAL0;
};
Vertex Declarations
In the vertex declaration, we see this:
public static VertexElement[] VertexElements =
{
new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0),
new VertexElement(sizeof (float)*3, VertexElementFormat.Color, VertexElementUsage.Color, 0),
new VertexElement(sizeof (float)*3 + 4, VertexElementFormat.Vector3, VertexElementUsage.Normal, 0),
};
Relates to the following shader code:
struct VertexShaderInput
{
float3 Position : POSITION0;
float4 Color : COLOR0;
float3 Normal : NORMAL0;
};
Vertex Declarations
In the vertex declaration, we see this:
public static VertexElement[] VertexElements =
{
new VertexElement(0, VertexElementFormat.Vector3, VertexElementUsage.Position, 0),
new VertexElement(sizeof (float)*3, VertexElementFormat.Color, VertexElementUsage.Color, 0),
new VertexElement(sizeof (float)*3 + 4, VertexElementFormat.Vector3, VertexElementUsage.Normal, 0),
};
Relates to the following shader code:
struct VertexShaderInput
{
float3 Position : POSITION0;
float4 Color : COLOR0;
float3 Normal : NORMAL0;
};
Creating shader file
Right click on Content Project
◦ Add -> New Item
Creating shader file
Right click on Content Project
◦ Add -> New Item
◦ Visual C# -> Effect File
Setting up the shader
Load the shader like any other resource
Effect effect = Content.Load<Effect>("ExampleShader");
Set the active technique
effect.CurrentTechnique = effect.Techniques["VertexColorsTechnique"];
Set shader global variables
effect.Parameters["World"].SetValue(Matrix.Identity);
effect.Parameters["View"].SetValue(Matrix.CreateLookAt(...));
effect.Parameters["Projection"].SetValue(Matrix.CreatePerspectiveFieldOfView(...));
Rendering using the shader
foreach (EffectPass pass in effect.CurrentTechnique.Passes)
{
pass.Apply();
// Rendering code here
}
Rendering using the shader
foreach (EffectPass pass in effect.CurrentTechnique.Passes)
{
pass.Apply();
// Rendering code here
GraphicsDevice.DrawUserIndexedPrimitives(PrimitiveType.TriangleList,
vertices, 0, vertices.Length, indices, 0, indices.Length/3);
}
In the draw function
effect.Parameters["World"].SetValue(Matrix.Identity);
effect.Parameters["View"].SetValue(Matrix.CreateLookAt(...));
effect.Parameters["Projection"].SetValue(Matrix.CreatePerspectiveFieldOfView(...));
foreach (EffectPass pass in effect.CurrentTechnique.Passes)
{
pass.Apply();
// Rendering code here
GraphicsDevice.DrawUserIndexedPrimitives(PrimitiveType.TriangleList,
vertices, 0, vertices.Length, indices, 0, indices.Length/3);
}
That’s it!
HLSL tips and tricks
Some useful things to know about HLSL
Just a quick glance, google it for details
Useful functions in HLSL
Vector length
◦ float len = length(myVector);
Normalize vector
◦ myNormal = normalize(myNormal);
Cross product
◦ float3 crossProduct = cross(forward, up);
Dot product
◦ float intensity = dot(normal, lightDirection);
Clamp value between [3,5]
◦ int x = clamp(y, 3, 5);
Clamp value between [0,1]
◦ int x = saturate(y);
◦ In some cases, this function is free!
Useful functions in HLSL
Other functions:
◦ abs, min, max, sin, cos, tan, pow, sqrt, exp, log, floor, lerp, smoothstep, reflect, refract, and many more..
Most common math functions are available
Just Google for ‘HLSL function name’ or ‘CG function name’
Sampling textures in HLSL
Define a texture global variable
◦ Texture2D MyTexture;
◦ Set its value in C#.
Then we define a texture sampler
sampler2D MySampler = sampler_state
{
texture = <MyTexture>;
magfilter = LINEAR;
minfilter = LINEAR;
mipfilter = LINEAR;
AddressU = mirror;
AddressV = mirror;
};
Sampling textures in HLSL
Now we need to ‘read’ the texture
◦ This is called sampling
◦ Lots of ways to do it
Sample function in HLSL
float4 color = tex2D(MySampler, float2(0.2, 0.3));
Note that we pass the sampler, not the texture.
Texture coordinates
◦ [0,1] range
◦ Usually you’d pass a variable (like interpolated texture coordinates)
Returns a float4
Sampling textures in HLSL
Lots of sampling functions available
◦ But you won’t need most of these
And these aren’t the only ones!
tex2D
tex2Dbias
tex2Dgrad
tex2Dlod
tex2Dproj
Sampling textures in HLSL
1D Textures
2D Textures
3D Textures
Cubemaps
All of these have their own sampling functions
◦ tex1D, tex2D, tex3D, texCUBE
Swizzling
Take a look at the following code
float4 a;
float4 b;
a = b.wyzx;
You can also reuse components
float4 a;
float4 b;
a = b.wyyx;
Or reuse one components four times
float4 a;
float4 b;
a = b.xxxx;
Swizzling
Generate a 2D vector from a 4D vector
float2 a;
float4 b;
a = b.xz;
Or a 4D vector from a 2D vector
float4 a;
float2 b;
a = b.xxyy;
Instead of .xyzw, we can also use .rgba
float4 a;
float4 b;
a = b.rgba;
Common errors
You’ve forgotten a semicolon
◦ ERROR: Unexpected token ‘something’
◦ Take a look at the line before the error
You misspelled variable names in C#
◦ Shader parameters and technique names are all CASE Sensitive!
Mesh doesn’t show up
◦ It’s probably the cullmode
◦ Or your World Matrix
◦ Or your View Matrix
◦ Or your Projection Matrix
◦ Or some other render state
◦ Or… I don’t know, it’s your code!
Common errors
Debugging shaders is hard
◦ Certainly harder than the CPU
◦ Can’t step through code, add breakpoints, etc.
◦ Can’t Console.WriteLine values
All is not lost though!
◦ Just don’t write any errors.
Common errors
Start with very simple shaders
◦ Don’t write everything and test it afterwards.
◦ Use a very simple pixel shader to write your vertex shader
float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
{
return float4(1,0,0,0);
}
◦ Make sure you test all the code you write. Lots of sanity checks!
◦ If you’ve finished with your vertex shader, write simple pixel shaders to test all the input
◦ Returning colors is kind of like Console.WriteLine()
float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0
{
return float4(input.Normal,0);
}
Common errors
Document every line of code
◦ It’s not that many lines of code anyway!
Use proper variable naming
◦ Indicate global variables
◦ If a vector is a normalized vector, call it myVectorN
◦ If a vector is in world space, call it positionW or positionWorld or worldPosition, just indicate it.
◦ Same thing with view space
◦ Same thing with projected coordinates
◦ If a vector points to the camera, call it toCamera, if it’s pointing to the camera and is normalized, call it
toCameraN
If there’s a built-in function for it, use it!
Test your vertex declaration
◦ Often the semantics in the C# vertex declaration and the HLSL struct don’t match
Help, my shader was working and now
it’s not working anymore!
Changed your shader code?
◦ Well, there’s your problem
Changed C# code?
◦ Some render state probably changed.
Render states changed by SpriteBatch
GraphicsDevice.BlendState = BlendState.AlphaBlend;
GraphicsDevice.DepthStencilState = DepthStencilState.None;
GraphicsDevice.RasterizerState = RasterizerState.CullCounterClockwise;
GraphicsDevice.SamplerStates[0] = SamplerState.LinearClamp;
You’ll need to change it back, even though you didn’t set it explicitly in the first place
GraphicsDevice.BlendState = BlendState.Opaque;
GraphicsDevice.DepthStencilState = DepthStencilState.Default;
Help, my shader was working and now
it’s not working anymore!
Some other shader may also have changed the render states
◦ Check this first
Some global variables might be incorrect
◦ Example:
◦ Render object 1 with a 100x scaling matrix
◦ Forget to set the world matrix back to 1x scaling
◦ Render object 2, which is so big, it gets clipped away
◦ You can check these values easily in C#
The End
ANY QUESTIONS?
Buy The Flock!
The End
ANY QUESTIONS?
