Texturing Massive Terrain

Texturing Massive Terrain Colt McAnlis

Graphics Programmer – Blizzard

60 minutes (ish)

What are we talking about?

Keys to Massive texturing

Texturing data is too large to fit into memory

Texturing data is unique

Lots of resolution Down to maybe 1meter / per pixel

What we’re ignoring

Vertex data General terrain texturing issues Low End Hardware Review of technologies

What We’re covering

Paging & Caches DXT++ Compression Compositing frameworks Editing Issues Example Based Texture Synthesis

The World : So Far..

What’s Visible?

Only subsection visible at a time Non-visible areas remain on disk

New pages must be streamed in Quickly limited by Disk I/O

Fast frustum movements kill perf New pages occur frequently

Radial Paging

Instead page in full radius around player Only need to stream in far-away pages

Distance based resolution

Chunks stream in levels of mip-maps As Distance changes, so does LOD New mip levels brought in from disk

Textures typically divided across chunk bounds Not ideal for Draw call counts..

Typical Setup

Each chunk has it’s own mipchain

Difficult To filter across boundaries

One mip to rule them..

But we don’t need full chains at each chunk Radial paging requires less memory

Would be nice to have easier filtering

What if we had one large mip-chain?

Mip Stack

Use one texture per ‘distance’ Resolution consistent for range

All textures are same size As distance increases, quality decreases

Can store as 3d texture / array Only bind 1 texture to GPU

Big textures

The benefit of this is that we can use 1 texture Texturing no longer a reason for

breaking batches No more filtering-across-boundary

issues 1 sample at 1 level gets proper filtering

Mip mapping still poses a problem though Since mips are separated out

Mipping solution

Each ‘distance’ only needs 2 mips Current mip, and the next smallest

At distance boundaries, mip levels should be identical. Current distance is mipped out to next

distance Memory vs. perf vs. quality tradeoff

YMMV

MipChain

Mip Transition

Updating the huge texture

How do we update the texture? GPU resource?

Should use render-to-texture to fill it. But what about compression?

Can’t RTT to compressed target GPU compress is limited

Not enough cycles for good quality Shouldn’t you be GPU bound??

So then use the CPU to fill it? Lock + memcpy

Compressing Textures

Goal : Fill large texture on CPU Problem : DXT is good

But other systems are better (JPG)

ID Software: JPEG->RGBA8->DXT Re-compressing decompressed streams

2nd level quality artifacts can be introduced Decompress / recompress speeds?

Compressing DXT

We have to end up at GPU friendly format Sooner or later..

Remove the Middle man? We would need to decompress directly to DXT Means we need to compress the DXT data MORE

Let’s look at DXT layout

High 565

Low 565

2 bit Selectors

DXT1 : Results in 4bpp

In reality you tend to have a lot of them :512x512 texture is 16k blocks

…

Really, two different types of data per texture

16 bit block colors 2bit selectors

Each one can be compressed even further

Block ColorsInput texture :

Potential for millions of colorsInput texture :

Actual used colors16 bit compressed

Used colors

•Two unique colors per block.•But what if that unique color exists in other blocks?• We’re duplicating data

•Let’s focus on trying to remove duplicates

Huffman Encoding

Lossless data compression Represents least-bit dictionary set

IE more frequently used values have smaller bit reps

String : AAAABBBCCD (80 bits)

Result : 00001010101101101111 (20 bits)

Symbol Used % Encode

A 50% 0

B 25% 10

C 15% 110

D 5% 111

Huffman block colors

More common colors will be given smaller indexes 4096 identical 565 colors = 8kb Huffman encoded = 514 bytes

4k single bits, one 16 bit color

Problem : As number of unique colors increases, Huffman becomes less effective.

Goal : Minimize Unique Colors

Similar colors can be quantized Human eye won’t notice

Vector Quantization Groups large data sets into correlated

groups Can replace group

elements withsingle value

Compressing Block Colors

Step #1 - Vectorize unique input colors Reduces the number of unique colors

Step #2 – Huffmanize quantized colors Per-DXT block, store the Huffman index

rather than the 565 color.

W00t..

Selector bits

Each selector block is a small number of bits

Chain 2bit selectors together to make larger symbol

Can use huffman on these too!

Huffman’s revenge!!

4x4 array of 2bit –per block values Results in four 8 bit values

Might be too small to get good compression results

Or a single 32 bit value Doesn’t help much if there’s a lot of unique

selectors

Do tests on your data to find the ideal size 8bit-16 bit works well in practice

DXT Data

Block Colors

Huffman Table

Selector Bits

Seperate

Q Block Colors

Vector Quantization

Huffman

Huffman Table

Huffman

Color Indexes

Selector Indexes

TO

DIS

K

Compressing DXT : rehash

Color Indexes

Selector Indexes

Huffman TableBlock Colors

Huffman TableSelector Bits

Fill DXT blocks

Decompressing

Results : 1024x1024 diffuse

Uncompressed DXT1 (4bpp) DXT1 ++

3mb 512kb 91kb

0.7 bpp

Results : 1024x1024 AO

Uncompressed DXT3A (4bpp) DXT ++

1mb 512kb 9kb

0.07 bpp

BACK UP!

Getting back to texturing.. Insert decompressed data into mip-

stack level Can lock the mip-stack level

Update the sub-region on the CPU

Decompression not the only way..

Paged data

Pages for the cache can come from anywhere Doesn’t have to be compressed unique

data What about splatting?

Standard screenspace method Can we use it to fill the cache?

Frame buffer splatting

Splatting is standard texturing method Re-render terrain to screen Bind new texture & alpha each time Results accumulated via blending

De facto for terrain texturing

2D Splatting : Compositing

Same process can work for our caching scheme Get same memory benefits

Don’t splat to screen space, Composite to page in the cache

What about compression? Can’t composite & compress

Alpha blending + DXT compress???

Composite->ARGB8->DXT

Why composite?

Compression is awesome But we could get better results

Repeating textures + low-res alpha = large memory wins

Decouples us from Verts overdraw Which is a great thing!

Why don’t composite?

Quality vs. Perf tradeoff Hard to get unique quality @ same perf More blends = worse perf

Trade uniqueness for memory Tiled features very visible.

Effectively wasting cycles Re-creating the same asset every frame

End Goal

Mix of compositing & decompression Fun ideas for foreground /

background Switch between them based on distance

Fun ideas for low-end platforms High end gets decompression Low end gets compositing

Fun ideas for doing both!

Cache

Disk Data

2D Compositor

CPU Compress

GPU Compress

Decompress

A really flexible pipeline..

Authoring issues

UR A T00L (programmer..)

Standard pipelines choke on data Designed for 1 user -> 1 asset work Mostly driven by source control setups

Need to address massive texturing directly

Multi-user editing

Problem with allowing multiple artists to texture a planet. 1 artist per planet is slow…

Standard Source Control concepts fail If all texturing is in one file, it can only

safely be edited by one person at a time Solution : 2 million separate files?

Need a better setup

Texture Control Server

Allows multiple users to edit texturing User Feedback is highly important

Edited areas are highlighted immediately to other users Highlighted means ‘has been changed’ Highlighted means ‘you can’t change’

Artist A Artist B

Texturing Server

Change Made Data Updated

Custom Submission

Custom merge tool required Each machine only checks in their

sparse changes

Server handles merges before submitting to actual source control Acts as ‘man in the middle’

Artist A Artist B

Texturing Server

Source Control

Changes Changes

Batching ideas

What about planet-sized batch operations? Could modify entire planet at once? Would ignore affected areas?

Double Edged Sword.. Important to still have batching. Maybe limit batch operation distances? Flag if trying to modify edited area?

Batch texture generation

Common texturing concepts Set texture by slope Set texture by height Set texture by area

Could we extend it further?

Complex interactions

View ‘set’ operations as ‘masks’ Set texturing by procedural functions

Combine masks in a graph setup Common concept

.kkriger, worldmachine, etc

Mask Graphs = good

Masks can re-generate based upon vertex changes As long as you store the graph, not the

mask. Generate multiple masks for other

data Apply trees, objects, etc

Cool algorithms here for all

Texture Tiling Problems

Repeating textures causes problems Takes more blends to reduce repetition

Increases Memory Increases perf Burden

Would be nice to fix that automagically

Example Based Texture Synthesis

Generates output texture per-pixel Chooses new pixel based upon current

neighborhood Represent input pixel as a function

of its neighbors Create search acceleration structure Find ‘neighborhood’ similar to input

This is known as ‘Per-pixel’ synthesis

Texture being synthesized

Exemplar

Issues

Basically a Nearest Neighbor search

Doesn’t give best quality Only correcting input pixel based upon

previously corrected neighborhood Introduces sequential dependencies

Need to increase neighborhood size to get better results

This increases sample time

Exemplar Noisy Output image

Appearance Texture Synthesis

Hoppe 2006 (Microsoft Research)

Multi-resolution: Fixes pixels at various sizes in output image This ‘keeps’ course texture features Reduces image artifacts

GPU based

Highly controllable Artists / mesh provided vector fields

For terrain

Can synthesize large textures Rather than have same repeating

texture Use terrain normals as input

Allows texture to ‘flow’ with contours Allow artists to adjust vectors

So they can paint custom swirls etc.

Could even use to synthesize terrain vertex data

But that’s another talk ;)

Issues

Still too slow to composite MASSIVE terrain @ edit time Synthesize the whole planet? Would have to be a render-farm process.

Actually, still too slow to do non-massive terrain.. Maybe generate custom decals?

But what about CPU? Multicore may shed light on it Future research?

In Conclusion

Use 1 Texture Resource for texture data MipStack structure

Use DXT++ to decrease footprint W/o using RGBA->DXT

Multi-input cache filling algorithms Stream + Composite

Use Custom texturing server Make texture synthesis Faster!!

I’m talking to you Mr. Hoppe ;)

Thank you! Andrew Foster Rich Geldreich

Ken Adams

[email protected]

Texturing Massive Terrain

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