Week 9 - Monday What did we talk about last time? Mipmapping - - PowerPoint PPT Presentation

Week 9 - Monday

 What did we talk about last time?  Mipmapping  Summed area tables  Anisotropic filtering

 We have been using BasicEffect to achieve most of our

shading

 BasicEffect gets so much done that it's tempting not to move

any further

 But more complex effects can be achieved by writing shader code

• urselves

 To start, open up the MonoGame pipepline, right-click on the

Content folder, and choose Add > New Item

 Choose Effect from the wizard and name it something that ends

with .fx

 We need to declare the variables we are going to use at the top of

the file

 These usually include at least the following (which are already

given in the template)

 We're also going to add an ambient and diffuse light

float4x4 World; float4x4 View; float4x4 Projection; float4x4 WorldInverseTranspose; float4 AmbientColor = float4(1, 1, 1, 1); float AmbientIntensity = 0.1; float4 DiffuseLightDirection = float4(0.7071f, 0.7071f, 0, 0); float4 DiffuseColor = float4(1, 1, 1, 1); float DiffuseIntensity = .5;

 We also have to define structures to take the input and the output  These vary because different vertex formats include different data (position,

normals, colors, texture coordinates)

 The simplest possible input and output would have position only  The POSITION0 is called a semantic  Semantics are used to tell the shader what the purpose of a variable is so that it

can pass the right data in and out

struct VertexShaderInput { float4 Position : POSITION0; float4 Normal : NORMAL0; }; struct VertexShaderOutput { float4 Position : POSITION0; float4 Color : COLOR0; };

 The job of the vertex shader is, at the very least, to transform a

vertex from model space to world space to view space to clip space

 It can also do normal and color calculations

VertexShaderOutput VertexShaderFunction(VertexShaderInput input){ VertexShaderOutput output; float4 worldPosition = mul(input.Position, World); float4 viewPosition = mul(worldPosition, View);

• utput.Position = mul(viewPosition, Projection);

float4 normal = mul(input.Normal, WorldInverseTranspose); float lightIntensity = dot(normal, normalize(DiffuseLightDirection));

• utput.Color = saturate(DiffuseColor * DiffuseIntensity * lightIntensity);

return output; }

 The pixel shader must find the final color of the pixel fragment  This pixel shader uses a diffuse shading model  The computed lighting is added to the ambient lighting

float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { return saturate(input.Color + AmbientColor * AmbientIntensity); }

 You're allowed to name your vertex and pixel shaders anything you want  You specify which you're going to use in a technique  At this level, techniques only have one pass, but it is possible to use

multiple techniques to achieve interesting effects

technique Diffuse { pass Pass1 { VertexShader = compile VS_SHADERMODEL VertexShaderFunction(); PixelShader = compile PS_SHADERMODEL PixelShaderFunction(); } }

 You have to load the shader like other content  Then, we run a loop similar to the earlier one, setting the parameters for the effect object effect = Content.Load<Effect>("Diffuse"); foreach( ModelMesh mesh in model.Meshes ) { foreach (ModelMeshPart part in mesh.MeshParts) { part.Effect = effect; effect.Parameters["World"]. SetValue(mesh.ParentBone.Transform * world); effect.Parameters["View"].SetValue(view); effect.Parameters["WorldInverseTranspose"]. SetValue(Matrix.Transpose(Matrix.Invert(mesh.ParentBone.Transform * world))); effect.Parameters["Projection"]. SetValue(projection); } mesh.Draw(); }

 Image textures are the most common, but 3D volume

textures can be used

 These textures store data in a (u, v, w) coordinate space  Even volume textures can be mipmapped

• Quadrilinear interpolation!

 In practice, volume textures are usually used for fog, smoke,

• r explosions
• 3D effects that are inconsistent over the volume

 A cube map is a kind of texture map with

6 faces

 Cube maps are used to texture surfaces

based on direction

 They are commonly used in environment

mapping

 A ray is made from the center of the cube

• ut to the surface
• The component with the largest magnitude

selects which of the 6 faces

• The other components are used for (u,v)

coordinates

 Cube maps can cause awkward seams

when jumping between faces

 You will never need to worry about this in this class, but

texture memory space is a huge problem

 There are many different caching strategies, similar ones used

for RAM:

• Least Recently Used (LRU): Swap out the least recently used

texture, very commonly used

• Most Recently Used (MRU): Swap out the most recently used

texture, use only during thrashing

 Prefetching can be useful to maintain consistent frame rates

 JPEG and PNG are common compression techniques for regular

images

 In graphics hardware, these are too complicated to be decoded on

the fly

• That's why the finished MonoGame projects have pre-processed.tkb

files

 Most DirectX texture compression divides textures into 4 x 4 tiles

• Two 16-bit RGB values are recorded for each tile
• Each texel uses 2 bits to select one of the two colors or two interpolated

values between them

 Ericsson texture compression (ETC) is used in OpenGL

• It breaks texels into 2 x 4 blocks with a single color
• It uses per-pixel luminance information to add detail to the blocks

 Normal maps (normals stored as textures) allow for interesting compression

approaches

• Only x and y components are needed since the z component can be calculated
• The x and y can then be stored using the BC5 format for two channels of color data

 A procedural texture is made by computing a function of u

and v instead of looking up a texel in an image

 Noise functions are often used to give an appearance of

randomness

 Volume textures can be generated on the fly  Values can be returned based on distance to certain feature

points (redder colors near heat, for example)

 Textures don't have to be static  The application can alter them over time  Alternatively, u and v values can be remapped to make the

texture appear to move

 Matrix transformations can be used for zoom, rotation,

shearing, etc.

 Video textures can be used to play back a movie in a texture  Blending between textures can allow an object to transform

like a chameleon

 The lighting we have discussed is based on material properties

• Diffuse color
• Specular color
• Smoothness coefficient m

 A texture can be used to modify these values on a per-pixel basis  A normal image texture can be considered a diffuse color map  One that affects specular colors is a specular color map (usually

grayscale)

 One that affects m is a gloss map

 Alpha values allow for interesting effects  Decaling is when you apply a texture that is mostly

transparent to a (usually already textured) surface

 Cutouts can be used to give the impression of a much

more complex underlying polygon

• 1-bit alpha doesn't require sorting
• Cutouts are not always convincing from every angle

 Bump mapping  BRDFs

 Make sure you're solid on bump mapping from Chapter 6  Read Chapter 7 (at a high level)  Finish Assignment 3

• Due tonight by midnight!

 Work on Project 2