三维可视化英文PPT汇.ppt

Simple Volume Rendering Fragment Shader void main( uniform float3 emissiveColor, uniform sampler3D dataTex, float3 texCoord : TEXCOORD0, float4 color : COLOR) { float a = tex3D(texCoord, dataTex); // Read 3D data texture color = a * emissiveColor; // Multiply by opac } Fragment Shader with Transfer Function void main( uniform sampler3D dataTex, uniform sampler1D tfTex, float3 texCoord : TEXCOORD0, float4 color : COLOR ) { float v = tex3d(texCoord, dataTex); // Read 3D data color = tex1d(v, tfTex); // transfer function } Local Illumination Blinn-Phong Shading Model Resulting = Ambient + Diffuse + Specular Local Illumination Blinn-Phong Shading Model Requires surface normal vector Whats the normal vector of a voxel? Resulting = Ambient + Diffuse + Specular Local Illumination Blinn-Phong Shading Model Requires surface normal vector Whats the normal vector of a voxel? Gradient Central differences between neighboring voxels Resulting = Ambient + Diffuse + Specular Local Illumination Compute on-the-fly within fragment shader Requires 6 texture fetches per calculation Precalculate on host and store in voxel data Requires 4x texture memory Pack into 3D RGBA texture to send to GPU Local Illumination Improve perception of depth Amplify surface structure Volumetric Shadows on GPU Light attenuated from light’s point of view CPU – Precomputed Light Transfer Secondary raymarch from sample to light source GPU Two-pass algorithm Modify proxy geometry slicing Render from both the eye and the light’s POV Two different frame buffers Two Pass Volume Rendering with Shadows Slice axis set half-way between view and light directions Allows each slice to be rendered from eye and light POV Render order for light – front-to-back Render order for eye – (a) front-to-back (b) back-to-front First Pass Render from eye Fragment shader Look up light color from light buffer bound as texture Multiply material color