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Special Image Effects

• Particle Systems

• Fog• Lens Flares• Shadows• Programmable Shaders

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Particle Systems

• Each particle is a point, line, or textured polygons (with transparency).

• Polygons can be oriented to always face the viewpoint (fire, water spray, explosions, weapon fire, etc.)

• Or textured onto surfaces (splats)• Usually thousands of particles are used

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Particle Systems• Particle Source

• Particle Attributes (can be static or functional)– Position– Velocity (speed and direction) – Color– Lifetime– Age– Shape– Size– Transparency

Shape

Point

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Particle Systems

• Simple concept, simple to implement…• However, a good implementation requires

some careful thought and consideration since you need to dynamically manage thousands of objects.

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Particle Systems

• Some links– Particle Systems by Allen Martin

• http://www.cs.wpi.edu/~matt/courses/cs563/talks/psys.html

– Gammasutra: Building an Advanced Particle System• http://www.gamasutra.com/features/20000623/vanderburg_01.htm

– Particle Systems API• http://www.cs.unc.edu/~davemc/Particle/• (demo taken from here)

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Fog

• Function of distance from the camera (linear or exponential)– as distance increases, bring colors to grey

• Can be done just with Z-buffer• Also can be used to reduce scene

complexity• Same idea can be used to fade far objects in

and out (prevents flickering)

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Fog example 1

MechWarrior 4: Mercenaries

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Fog example 2

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Billboard objects

• Textured polygons that rotate to stay flat towards the eye.

• Used often for trees, trees, clouds, smoke, explosions, lens effects, etc.

Red Faction 3 - PC

Another way to do trees, bushes, telephone poles, etc. without reorienting polygons each frame

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Lens Effects• Billboards at varying levels of depth.• Usually rendered last.• Sometimes just an overlay on the screen.

From http://www.geocities.com/SiliconValley/Lakes/1434/lenseffects.html

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Lens animation

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Lens Effects – Asheron’s Call 2

Asheron’s Call 2

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Shadows

• Projected shadows on flat surfaces (project polygon onto surface)

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Soft Shadows

• Multiple light sources or area sources give soft shadows (umbra, penumbra)

penumbra

umbra

penumbra

umbra

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Soft Shadows

From http://www.stereopsis.com/shadow/

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Shadow Volumes

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Programmable Shaders

• Renderman was the first programmable shading language

• DirectX 8 featured vertex and pixel shaders• Nvidia and ATI boards now have

programmable shading capabilities

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Direct3D Pipeline

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Shaders

• Vertex Shaders: – procedural geometry deformation – range-based or radial fog effects – camera lens effects including fish eye, wide angle, and

water refraction effects.

• Pixel Shaders: – per-pixel reflections – per-pixel lighting using Phong-style shading or DOT3

effects – procedural textures

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Cg Vertex Shader Examples

Anisotropic Lighting Fog

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Cg Vertex Shader Examples

Stencil Shadow VolumesRefract Reflect Demo

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Cg Pixel Shader Examples

Soft Stencil Shadows Hardware Shadow Maps

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Cg Pixel Shader Examples

Water InteractionFlare

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Cg Shader Examples

Firehttp://www.cgshaders.org/shaders/show.php?id=39

Shadow volumes w/foghttp://www.cgshaders.org/shaders/show.php?id=49