Transcript Document 7459404

Walk-Through Illustrations:
Frame-Coherent Pen-and-Ink
Style in a Game Engine
Bert Greudenberg
Maic Masuch
Thomas Strothotte
It Looks All Crappy
Cartman: Aw, screw it. It
probably isn't all that
good anyway.
Kyle: Cartman! What are
you talking about?! You
LOVE Terrance and
Phillip!
Cartman: Yeah, but the
animation's all crappy —
it probably can't sustain
itself over ninety minutes.
Who wants crappy animation?
• Tired of the gothic space dungeons?
• Tired of “realistic” animation that fools you
for five seconds?
• You need a change
• A non-photorealistic change!
3D Game Engines
• 3D game engines have
made huge advances
• Engines primarily still
focus on photorealistic
images
• Game images are
technically non
photorealistic
NPR Here to Stay
• Research has turned
•
•
to NPR of still images
Great advances in
Toon, Painterly, and
Pen & Ink (i.e. South
Park)
However, animating
NPR or real-time
rendering 2 problems
occur.
What’s the Problem?
• Maintenance of frame-to-frame coherence
– Hidden Surface Removal
• Objects appear and disappear correctly
• Ability of a 3D engine to render NP images
in real time
Solution!
• Create an engine that facilitates a hybrid
rendering pipeline
• Allows specification of the rendering style
on a per object basis
More to follow
Computer Games and NPR
• No games achieves
•
true photorealism
Rendering style can
be called
photorealistic
– Shapes, spatial
relationships, surface
details
NPR Video Games
• Very few games
•
incorporate NPR
elements
Examples:
– Cartoon Rendering
– Pen & Ink
•
Broken Arrow
Cartoon Rendering
• Shading Model in 2D
cartoon
– Games only use 2D
data.
– Visually appealing, but
not that interactive
• Monkey Island III
• Broken Sword
Monkey Island III
Pen and Ink Rendering
• NPRQuake by Gleicher
• Intercepts the calls to
•
•
graphics libraries
Replaces them with
different drawing
primitives
Uses core GLQuake
engine and maintains
gameplay
NPRQuake Sketch
NPRQuake Blue-Print
NPRQuake Brush-Stroke
Problems with NPRQuake
• Achieves non-photorealistic look
• Style elements do not preserve frame
coherence
– Outlines of objects vary from frame to frame
– Results in lively but disturbing experience
How to Fix It?
• Few systems deal with frame to frame
coherence.
• Many systems can create Pen & Ink
illustrations
– But, probability is used to model the line
deviations of hand drawings
• Not suitable for real time rendering in animations
Non-Photorealistic Visualization
In Game Engine
• NP imaging allows the
user to simplify an image
by omitting details to
control the viewer’s
attention
– Emphasize, Deemphasize
certain elements of a scene
• Aim for pen-and-ink
illustrations
– Silhouettes and creases are
clearly drawn
– Surface detail added
through hatching
Hybrid Rendering Pipeline
• Able to specify rendering style of each object
– Gain additional freedom in expression for the
visualization
• Photorealistic Images – use normal texture
•
•
mapping and shading
NP Images – consist of modified shading, an
outline, and NP textures (ink maps or hatch
maps)
Hybrid – combine photorealistic rendering and
NP drawing styles
NP Elements in 3D Game Engine
• Properties of 3D game engine
– Provide player with highly immersive
experience
• Enhace speed, realism, and image quality
– Preprocess as much data as possible
– Let hardware handle most of the per-frame
load
• Mip-Mapping, anti-aliasing
NP Elements in 3D Game Engine
• Non-Photorealism uses image space
elements
– Pixels generated on the screen are not a strict
projection of the 3D scene objects
– A triangle outline rendered as lines has a
constant width independent of the actual
distance of the triangle to the viewer
Outlining
• Silhouettes
– Drawn to enhance the visual separation of objects from each
other and background
– Silhouette edges need to be determined every frame
– Non-Convex edges are never drawn (second)
– Sharp Edges are always drawn (third)
– Only smooth convex edges are drawn (fourth)
– Result with hidden lines removed
Hatching
• Textures are supposed to become smaller with
•
increasing distance
Hatching
– shade by drawing or etching fine parallel or perpendicular lines
– Pen & Ink hatching textures cause serious moire´e patterns
– In motion this produces even worse artifacts than still images
• Prevents frame coherence
How to Fix This?
•
Common antidote
–
–
–
Mip-mapping
Unfortunately, normal filtering process applied to large white
areas and thin black lines of hatching texture cause lines to
vanish
Visible structure is lost
Hatch Maps
• Normal mip-mapping
– Lines are black and well
separated at the top level
– Become lighter and closer
at lower levels
• Hatch Map
– Equally space black hatch
lines for all mip-map levels
– Only very lowest levels are
gray values used to
maintain tone
Hatch Maps
• Unfortunately, all over tone is not continuous
• Abrupt switch between hatch-map levels
• Use Tri-linear Filtering
Ink Maps
• Hatching is a mechanical process
• Hybrid Pipeline
– Photorealistic: Mip-Mapping
– Non-Photorealistic: Ink Map
• Adding details to surfaces is artistically challenging
• Construct ink maps
– Smooth animation achieved with carefully crafted ink maps
– Frame Coherence is maintained using tri-linear filtering
What They Achieved
• Part of a medieval palace created for the
UNREAL engine
What they Achieved
Specifications
• 3D engine runs on:
– 750 MHz CPU
– GeForce2 ultra graphics card
• Even on unoptimized models, engine runs
at interactive speeds, i.e. 25 fps
And Now….Zelda!!!
• The Legend of Zelda: The Wind Wakers
• Right now, this is the pinnacle of NPR in
game engines.
– First game to max out hardware of Nintendo
Gamecube
– Combines great use of interactive 3D and NPR
Screenshots
More
Zelda Video!!
Thank You
Any Questions?