Graphics Graphics Korea University cgvr.korea.ac.kr 1 Surface Rendering Methods 고려대학교 컴퓨터 그래픽스 연구실

CGVR Graphics Korea University cgvr.korea.ac.kr 2 Surface Rendering: Shading Determine a Color for Each Filled Pixel How to Choose a Color for Each Filled Pixel Each illumination calculation for a ray from the eyepoint through the view plane provides a radiance sample

CGVR Graphics Korea University cgvr.korea.ac.kr 3 Shading Methods Ray Casting Polygon Shading Ray Tracing Radiosity

CGVR Graphics Korea University cgvr.korea.ac.kr 4 Ray Casting Simplest Shading Approach Perform independent lighting calculation for every pixel

CGVR Graphics Korea University cgvr.korea.ac.kr 5 Polygon Shading Can Take Advantage of Spatial Coherence Illumination calculations for pixels covered by same primitive are related to each other

CGVR Graphics Korea University cgvr.korea.ac.kr 6 Polygon Shading Algorithms Flat Shading Gouraud Shading Phong Shading

CGVR Graphics Korea University cgvr.korea.ac.kr 7 Polygon Shading Algorithms Flat Shading Gouraud Shading Phong Shading

CGVR Graphics Korea University cgvr.korea.ac.kr 8 Flat Shading Illuminated only by directional light sources Diffuse or viewed from infinitely far away

CGVR Graphics Korea University cgvr.korea.ac.kr 9 Flat Shading One Illumination Calculation per Polygon Assign all pixels inside each polygon the same color

CGVR Graphics Korea University cgvr.korea.ac.kr 10 Flat Shading Objects Look Like They are Composed of Polygons OK for polyhedral objects Not so good for ones with smooth surfaces

CGVR Graphics Korea University cgvr.korea.ac.kr 11 Polygon Shading Algorithms Flat Shading Gouraud Shading Phong Shading

CGVR Graphics Korea University cgvr.korea.ac.kr 12 Gouraud Shading Smooth Surface Represented by polygonal mesh with a normal at each vertex

CGVR Graphics Korea University cgvr.korea.ac.kr 13 Gouraud Shading One Lighting Calculation per Vertex Assign pixels inside polygon by interpolating colors computed at vertices ViewerLight N1N1 N3N3 N2N2 V1V1 L1L1 Polygon

CGVR Graphics Korea University cgvr.korea.ac.kr 14 Gouraud Shading Bilinearly Interpolate Colors at Vertices Down and Across Scan Lines I1I1 I2I2 I3I3

CGVR Graphics Korea University cgvr.korea.ac.kr 15 Gouraud Shading Smooth Shading over Adjacent Polygons Curved surfaces Illumination highlights Soft shadows Mesh with shared normals at vertices

CGVR Graphics Korea University cgvr.korea.ac.kr 16 Gouraud Shading Produces Smoothly Shaded Polygonal Mesh Piecewise linear approximation Need fine mesh to capture subtle lighting effects Flat ShadingGouraud Shading

CGVR Graphics Korea University cgvr.korea.ac.kr 17 Polygon Shading Algorithms Flat Shading Gouraud Shading Phong Shading

CGVR Graphics Korea University cgvr.korea.ac.kr 18 Phong Shading What if Polygonal Mesh is too Coarse to Capture Illumination Effects in Polygon Interiors? ViewerLight N1N1 N3N3 N2N2 V1V1 L1L1 Polygon

CGVR Graphics Korea University cgvr.korea.ac.kr 19 Phong Shading One Lighting Calculation per Pixel Approximate surface normals for points inside polygons by bilinear interpolation of normals from vertices ViewerLight N1N1 N3N3 N2N2 VL Polygon N

CGVR Graphics Korea University cgvr.korea.ac.kr 20 Phong Shading Bilinearly Interpolate Normals at Vertices Down and Across Scan Lines αβ γ N1N1 N2N2 N3N3

CGVR Graphics Korea University cgvr.korea.ac.kr 21 Phong Shading Gouraud Wireframe Phong Flat

CGVR Graphics Korea University cgvr.korea.ac.kr 22 Shading & Subdivision GouraudPhongFlat Loop Subdivision Level 1 Level 2 Control Mesh

CGVR Graphics Korea University cgvr.korea.ac.kr 23 Shading Methods Ray Casting Polygon Shading Ray Tracing Radiosity

CGVR Graphics Korea University cgvr.korea.ac.kr 24 Ray Tracing Extension of Ray Casting Look for the visible surface for each pixel Continue to bounce the ray around the scene

CGVR Graphics Korea University cgvr.korea.ac.kr 25 Ray Tracing Global Illumination Shadows Refractions Inter-object reflections Highly Realistic vs. Computation Time Transparency Reflectance Shadow

CGVR Graphics Korea University cgvr.korea.ac.kr 26 Basic Ray Tracing Algorithm For Each Pixel Ray Primary ray  Test each surface if it is intersected Intersected: Secondary ray  Reflection ray  Transparent – Refraction ray

CGVR Graphics Korea University cgvr.korea.ac.kr 27 Basic Ray Tracing Algorithm For Each Pixel Ray Primary ray  Test each surface if it is intersected Intersected: Secondary ray  Reflection ray  Transparent – Refraction ray

CGVR Graphics Korea University cgvr.korea.ac.kr 28 Ray Tracing Tree Ray tree represents illumination computation One branch  reflection The other branch  transmission Terminated  reach the preset maximum or strike a light source SceneRay Tree

CGVR Graphics Korea University cgvr.korea.ac.kr 29 Ray Tracing Tree Pixel intensity Sum of intensities at root node Start at terminal node If no surfaces are intersected, the intensity of background SceneRay Tree I back I pixel

CGVR Graphics Korea University cgvr.korea.ac.kr 30 Shading Methods Ray Casting Polygon Shading Ray Tracing Radiosity

CGVR Graphics Korea University cgvr.korea.ac.kr 31 Radiosity Goal Simulate diffuse inter-object reflections and shadows

CGVR Graphics Korea University cgvr.korea.ac.kr 32 Radiosity Basic Idea Treat every polygon as light source

CGVR Graphics Korea University cgvr.korea.ac.kr 33 Radiosity Advantages Physically models shadows and indirect diffuse illumination Independent of any viewpoint Equation B i = Radiosity of patch i E i = Emission of patch i ρ i = Reflectivity of patch i F i = Form-factor between patches i and j

CGVR Graphics Korea University cgvr.korea.ac.kr 34 Form Factors Definition Fraction of energy leaving patch j that arrives at patch i Computation Project onto unit hemisphere Project onto unit circle base Divide by area of circle Project scene onto hemi-cube Project onto unit hemisphere Project onto Hemi-cube

CGVR Graphics Korea University cgvr.korea.ac.kr 35 Matrix Solution Methods Matrix Formulation Progressive Refinement Iterate shoot radiosity from patches O(n 2 ) computation, but get pretty good solutions more quickly

CGVR Graphics Korea University cgvr.korea.ac.kr 36 Matrix Solution Methods 24 iterations 1 iteration 100 iterations 2 iterations

CGVR Graphics Korea University cgvr.korea.ac.kr 37 Hierarchical Radiosity Multiresolution Computation Substructure patches into quad-tree Transfer energy using lower resolution mesh elements if can do so within error tolerance O(n) computation

CGVR Graphics Korea University cgvr.korea.ac.kr 38 Ray Tracing & Radiosity Dilemma: Radiosity is good at diffuse inter-object reflection Ray tracing is good at specular inter-object reflection Combine them Example: compute diffuse inter-object reflections in a ray tracer Monte Carlo methods

CGVR Graphics Korea University cgvr.korea.ac.kr 39 Summary Ray Casting Flat Gouraud Phong Ray Tracing Radiosity Less Expensive More Accurate

CGVR Graphics Korea University cgvr.korea.ac.kr 40 Visible-Line Determination

CGVR Graphics Korea University cgvr.korea.ac.kr 41 Visible-Surface Determination with Ambient Illumination only

CGVR Graphics Korea University cgvr.korea.ac.kr 42 Individually Shaded Polygons with Diffuse Reflection

CGVR Graphics Korea University cgvr.korea.ac.kr 43 Gouraud Shaded Polygons with Diffuse Reflection

CGVR Graphics Korea University cgvr.korea.ac.kr 44 Gouraud Shaded Polygons with Specular Reflection

CGVR Graphics Korea University cgvr.korea.ac.kr 45 Phong Shaded Polygons with Specular Reflection

CGVR Graphics Korea University cgvr.korea.ac.kr 46 Curved Surfaces with Specular Reflection

CGVR Graphics Korea University cgvr.korea.ac.kr 47 Improved Illumination Model and Multiple Lights

CGVR Graphics Korea University cgvr.korea.ac.kr 48 Texture Mapping

CGVR Graphics Korea University cgvr.korea.ac.kr 49 Displacement Mapping

CGVR Graphics Korea University cgvr.korea.ac.kr 50 Reflection Mapping