Billboards A texture mapped polygon, which always faces ...computer-graphics.se/TSBK07/files/pdf18/9c billboards.pdf · Billboards!! A texture mapped polygon, which always faces the

Information Coding / Computer Graphics, ISY, LiTH

Billboards!!

A texture mapped polygon, which always faces the viewer

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Billboards!!

2D images placed on surfaces that are always facing the camera!

!“Sprites” in older action games!

!Advanced version: “impostors”!

!Often used for complex objects even today!

!Example: forests

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Classic example: Doom!!

Big billboards. No 3D models.

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Classic example: Dark Forces!!

Big billboards. Some 3D models.

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Problem with too few views.

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Implementing billboards!!

• Billboards generally need transparency!!!!!!!!!!

=> Special care is needed to avoid problems with Z-buffering!

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Transparency!!

1) Sort by distance (Painter's algorithm)!!

• Perfect results!• Supports semi-transparency!

• Required sorting and a separate stage!!

2) Discard fragments!!

• No semi-transparency!• Some artifacts at edges!

•Very easy

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#version 150!!out vec4 outColor;!!in vec2 texCoord;!uniform sampler2D tex;!!void main(void)!{!!vec4 t = texture(tex, texCoord);!!if (t.a < 0.01) discard;!!else!!!outColor = t;!}

discard; as cheap!solution to transparency

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• Texture files must support transparency!!!

File formats:!!

TGA!PNG!!

TGA: simple format, good for demos!!

Libraries for PNG:!libPNG!

PNGlite by Daniel Karling

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Variants:!!

• World oriented billboard!• Viewpoint oriented billboard (face the

camera in full 3D)!• Axial (viewpoint) billboard!

• View plane oriented billboard!• View plane oriented axial billboard

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View plane oriented billboard!!

Easy! Zero out rotation!!!

Good - no overlaps!

View plane oriented

Viewpoint oriented

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Axial billboard!!

Rotate around Y

Axial!Suitable for

trees etc

Non-axial

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Full 3D viewpoint oriented billboard!!

Change of basis solution!!

Z vector from viewpoint, pick an up vector (usually Y axis), form basis with cross products

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World oriented billboard!!

No camera dependent rotation

Example: Tomb Raider 2 Terracotta warriors (Temple of Xian)

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A grid of billboards

Non-axial AxialViewpoint oriented

View plane oriented

World oriented billboard not in grid

Construct basis

Clear rotations

Construct axial rotation

Construct basis based on view

plane

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Billboard variants1) Always facing the camera.!One triangle or quad is enough!

2) A few polygons.!Good for world oriented billboards.

3) Multiple billboards.!Simplify complex objects om moderate distance.

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Temple of Xian!!

Statues behind first row are billboards!

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Billboard variants!!

The objects on the plate are billboards - some 2-poly!

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Application: Particle systems!!

Explosions, rain, fountains, smoke...!!

Excellent billboarding application!!

Many small objects - good opportunities to ”cheat” with transparency problems

More about this in the Animation part!

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Impostors!!

”Live” billboards!!

Render to texture, update sometimes!!

Render as other billboards!!

Decide when to update

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Large worlds, conclusions!!

HIgh-level VSD to limit processing to visible parts - start with frustum culling!

!Level-of-detail to reduce unneccessary processing of

detailed models!!

Use billboards for extreme simplification on large distance, particle effects etc!

!!

If we can’t see the difference, use the cheaper solution!

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Documents

Billboards A texture mapped polygon, which always faces ...computer-graphics.se/TSBK07/files/pdf18/9c billboards.pdf · Billboards!! A texture mapped polygon, which always faces the