Background Caches for Large Outdoor Scenes Bill Hess

Motivation:

Motivation:

View Frustum Volume enclosed by 6 planes Volume enclosed by 6 planes Objects outside the frustum are not drawn Objects outside the frustum are not drawn Back plane decides how deep the scene is Back plane decides how deep the scene is

Problem: Depth Buffer Geometry depth is stored at every pixel Geometry depth is stored at every pixel Allows objects to be drawn in any order Allows objects to be drawn in any order Allows objects to intersect each other Allows objects to intersect each other Depth buffer precision is fixed in hardware Depth buffer precision is fixed in hardware Multiple scene depths can map to one depth buffer value Multiple scene depths can map to one depth buffer value As the back plane is pushed back, the range of values that can map to the same depth value increases As the back plane is pushed back, the range of values that can map to the same depth value increases

Problem: Depth Buffer

Problem: Projection View Frustum volume increases with the cube of the scene depth View Frustum volume increases with the cube of the scene depth Potentially 8 times more geometry to draw just to double scene depth Potentially 8 times more geometry to draw just to double scene depth

Solution Draw backgrounds less frequently Draw backgrounds less frequently Draw background as a flat image Draw background as a flat image Common methods Common methods Render/Draw backgrounds ahead of time Render/Draw backgrounds ahead of time Render backgrounds into a texture at run-time Render backgrounds into a texture at run-time

Skybox Scene surrounded by a textured cube Scene surrounded by a textured cube Cube is textured with a backdrop representing the background Cube is textured with a backdrop representing the background Cube does not move with the scene Cube does not move with the scene Appears “infinitely” far away Appears “infinitely” far away

Skybox limitations Players can never reach the background Players can never reach the background Gap between foreground and background Gap between foreground and background No parallax effect No parallax effect Really only good for… sky. Really only good for… sky.

3D Skybox Used in Valve’s Source engine Used in Valve’s Source engine Background geometry is drawn to 1:16 scale in a hidden part of the map Background geometry is drawn to 1:16 scale in a hidden part of the map Camera is placed into the “skybox” to render the background Camera is placed into the “skybox” to render the background Use the depth buffer twice Use the depth buffer twice Background is only a mockup, not explorable Background is only a mockup, not explorable

Related Research Pre-Computed backgrounds Pre-Computed backgrounds Scene is broken into view-cells Scene is broken into view-cells Backgrounds are stored on disk Backgrounds are stored on disk City walkthrough City walkthrough Buildings are rendered to flat Impostors Buildings are rendered to flat Impostors Camera is constrained to street tracks Camera is constrained to street tracks

Layered Depth Images Render scene but record multiple colors and depths at each pixel Render scene but record multiple colors and depths at each pixel Use inverse camera transformation to reposition each pixel for a new camera angle Use inverse camera transformation to reposition each pixel for a new camera angle Parallax effect Parallax effect Hidden surfaces are revealed Hidden surfaces are revealed Storage required equal to depth complexity of the image (max number of overlapping objects) Storage required equal to depth complexity of the image (max number of overlapping objects)

Goal Dynamically generate background images Dynamically generate background images Show parallax for view changes Show parallax for view changes Transition between background and foreground Transition between background and foreground Work in real-time Work in real-time Combination of Skybox and Layered Depth Image Combination of Skybox and Layered Depth Image

Work So Far Recreate the problem Recreate the problem

Work So Far