Practical 3 Introduction Paul Scharf Tom Rijnbeek Practical 3 - PowerPoint PPT Presentation

Practical 3 Introduction Paul Scharf Tom Rijnbeek

Practical 3 Advanced Shader Programming • 18 tasks: 6 easy; 7 medium; 5 hard • Easy exercises: choose 4 out of 6 – Maximum grade: 8 • Two more points by doing either: – Two medium tasks – One hard task • Deadline: Thursday June 26, 23:59

EASY TASKS

[E1] Multiple light sources • Repeat light calculations for every source

[E2] Spotlight

[E3] Cel shading • Discretised shading smooth

[E3] Cel shading • Easy solution: use texture for spectrum • More complicated: – Discretise mathematically – Use gradients for smoothing

[E4] Frustrum culling • Only draw visible models • Calculated on the CPU

[E4] Frustrum culling • Frustrum bounded by six planes • Don’t draw models on the wrong side of planes • Or use XNA’s BoundingFrustrum class...

Post-processing basics 1. Render scene to texture (rendertarget) 2. Render screen-filling quad sampling from texture in pixel shader • XNA: draw texture with Spritebatch using pixel shader

[E5] Simple colour filter • Apply grey-scale filter to every pixel • Use weighted sum: 𝑍 = 0.3𝑆 + 0.59𝐻 + 0.11𝐶

[E6] Gaussian blur • Box blur : average pixels in a square area around target pixel • Calculate by applying a convolution kernel on the image 1/9 1/9 1/9 1/9 1/9 1/9 1/9 1/9 1/9

[E6] Gaussian blur • Gaussian blur: average pixels in a (roughly) circular area around target pixel • Use normal distribution to build kernel

[E6] Gaussian blur 0.00000067 0.00002292 0.00019117 0.00038771 0.00019117 0.00002292 0.00000067 0.00002292 0.00078633 0.00655965 0.01330373 0.00655965 0.00078633 0.00002292 0.00019117 0.00655965 0.05472157 0.11098164 0.05472157 0.00655965 0.00019117 0.00038771 0.01330373 0.11098164 0.22508352 0.11098164 0.01330373 0.00038771 0.00019117 0.00655965 0.05472157 0.11098164 0.05472157 0.00655965 0.00019117 0.00002292 0.00078633 0.00655965 0.01330373 0.00655965 0.00078633 0.00002292 0.00000067 0.00002292 0.00019117 0.00038771 0.00019117 0.00002292 0.00000067

[E6] Gaussian blur • Convolution can be heavily optimised • Split in vertical and horizontal pass 1 3 1 9 1 9 1 9 1 3 ∗ 1 3 1 3 1 3 1 9 1 9 1 9 = 1 3 1 9 1 9 1 9

MEDIUM TASKS

[M1] Textured light • Create view & projection matrix for light • Transform vertex position twice

[M2] Shadow mapping • Render depth texture from light • Render scene normally – Compare pixel’s distance to light with value from depth texture

[M2] Shadow mapping depth from light from camera distance compare to light pictures from: http://en.wikipedia.org/wiki/Shadow_mapping

[M3] Reflection • Render scene from reflected camera • Render to texture – Render mirror with texture • Or: use stencil buffer – Mask mirror pixels, to only render reflection there

[M4] Cube mapping • Cube map: texture represting lighting from all directions

[M4] Cube mapping • Calculate reflection vector • Use cube texture lookup to find reflected colour

[H5] Advanced cube mapping • Precomputed diffuse light map • Stronger reflections at shallow reflection angles

[M5] Transparency • Render transparent objects after opaque ones • Sort transparent objects back-to-front

[M6] Post-processing: Bloom • Render scene • Threshold bright pixels • Downscale and blur repeatedly • Add up all scales

[M6] Post-processing: Bloom threshold all added up scale down and blur

[M7] Post-processing: God rays • Volumetric light scattering through dust/mist • Approximate in screen-space

HARD TASKS

[H1] HDR Lighting & Tone Mapping • Simulate adaption of human eye to changing brightness • LDR vs. HDR – LDR [0, 1] – HDR [0, ∞) • Tone Mapping: HDR  LDR

[H2] Deferred Shading • Earlier lighting methods inefficient with many lights • Render geometry information to multiple rendertargets (G-buffers) • Calculate lighting per light for affected pixels

[H2] Deferred Shading Diffuse Colour Depth/Position Normal Tons of lights

[H3] Parallax Mapping • Use height map to displace diffuse texture

[H4] Post-processing: SSAO

[H4] Post-processing: SSAO • Crude approximation of full global illumination • Calculate in screen- space • First real-time implementation: Crysis

Final words • Try focusing on doing few tasks well rather than lots of exercises poorly • Finish the easy tasks first • Start in time!

Recap • Finish 4 easy tasks for an 8 • Finish 2 medium tasks or 1 hard task for 2 points • Additional tasks don’t improve grade • Start in time!

Questions?