six 2D textures

Transcrição

six 2D textures

Bachelor Praktikum:
Echtzeitgraphik in C++ und DirectX10
computer graphics & visualization
Proto-Texturing
• Idea:
– Set of textures that serve as prototypes for different
materials (e.g. sand, grass, rock, snow, etc.)
– Height/slope-dependent weighting function to
decide how the textures are blended for a single
fragment
3D Praktikum WS 2009/2010 – Echtzeitgraphik in C++ und DirectX10
K. Bürger, S. Auer, Prof. Dr. Westermann
Proto-Texturing
• Pre-Processing:
– Store the precomputed weight
function in a RGBA-texture
Slope
– Weights for the different
materials are stored in the
distinct color channels
– Sum of weights should be 1
Height
Sand
Grass
Rock
Snow
Proto-Texturing
• How to texture a specific fragment?
1. Use height and slope as texture
coordinates to determine the
according weights
2. Use xz-coordinate as (scaled)
texture coordinate to access the
proto textures
3. Fetch samples from the proto
textures and blend them according
to the given weights
Environment Mapping
• An “advanced texturing” method in computer
graphics, which is used to
approximate reflections in
curved surfaces
Cubic Environment Mapping
• Idea:
– The Environment Map is
composed of six 2D textures,
representing the view from
the center of the box in the
orthogonal viewing directions
– Object is thought to be placed
at the center of the box and
the direction of the reflectance rays are used to
determine the reflected color of the environment
• Assumptions:
– Object is at the center of the cube
– Distance between object and cube (and its pictured
surroundings) is (near) infinity (or far enough)
• Given:
– normal n, position p (-> view vector v)
• Approach:
1. Compute reflection vector r
2. Assuming that p is in the center of the cube:
• Largest component and sign determines the cube face
• The two other components are adapted to the texture
space and devided by the largest component in order to
get the texture coordinates within the cube face.
• Note: cube map sampling is directly supported by HLSL!
Using Cubemaps
Application (Loading the resource):
Use the D3DX10CreateShaderResourceViewFromFile() function and cubemaps
in .dds Format (available on the couse homepage), so DirectX will automatically
create CubeMap resouce (Texture2DArray with special settings...)
HLSL sample code to access a cube map resource:
TextureCube2D myCubeMap;
//the Cube Map
float4 PSTextured(float4 pos : SV_Position, float3 wp : WORLDPOS, float3 normal : NORMAL) : SV_Target0{
//Calculate reflection vector based on incident view direction and surface normal
float3 incident = normalize(g_vEyePos - wp);
float3 R = reflect(incident, normalize(normal));
return myCubeMap.Sample( mySampler, R ).rgba; // a 3 component vector is needed to sample a cubemap
}
Environment
How can we colorize the background with the cubemap ?
Render „SkyBox or SkyDome“ textured with CubeMap Faces
Render single quad covering the whole viewport and calculate cubemap
intersection analytically
Environment
(0,0)
(Width-1,0)
(1,0)
(1,2)
(0.143,0.111)
(0,Height-1)
(0,1)
(Width-1,Height-1)
(1,1)
Inside a pixelshader we can always access the system value SV_Position, whose
x and y components contain a fragments position in texelcoordinates !
Normalize those values trough division by (Width-1, Height-1)
Environment
Normalized Device Coordinates (a position projected onto the imageplane,
after perspective transformation and dehomogenization) range from [-1,1] in
the xy-Domain (plus a nonlinear depthvalue for z-Testing)
(-1,1)
x
(1,1)
y
(0,-1)
(1,-1)
Shift Coordinates into NDC range: x = 2∙x -1, y = 1-2∙y
Environment
• We also know that the Camera is located at the origin of the view coordinate system
and looks down the +z-Axis.
• Based on camera parameters we can transform NDC coordinates into a vector from
the camera trought the image plane by scaling the normalized device coordinates
accordingly („fan out the view rays...“!)
x
1
FoV
-1
y
Vec3 ViewVec= Vec3(AspectRatio∙tan(0.5f∙FieldOfView)∙x, tan(0.5f∙FieldOfView)∙y, 1.0f);
Environment
• Multiplication with the inverse View-Matrix then transforms the
view rays back to worldspace, where they can be used as
CubeMap-Lookup coordinates.
Assignment 7
1. Proto-Textures:
–
–
–
–
Different tetures for sand, grass, rock, snow.
Pre-process weights and write them into a texture.
Use Height/slope to determine weights.
Use weights to blend the different material textures.
2. Cubic Environment Mapping
– Create a water surface on a specific height.
– Use cube map to approximate the reflexions of the
environment on the water surface.
3. Environment
– Use the cube map to render the environment around the
terrain.

six 2D textures

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