Screen Space Decals in Warhammer 40,000: Space Marine

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 This subtitle is 20 points
 Screen
Bullets are blue Space Decals
 They have 110% line spacing, 2 Spacebefore & after
in Warhammer 40,000: points Marine
 Longer bullets in the form of a paragraph are harder to
read if there is insufficient line spacing. This is the
maximum recommended number of lines per slidePope Kim
Sr. Graphics Programmer
(seven). Relic Entertainment (past)
 Sub bullets look like this

Traditional Decals

 Sometime between 2008
This subtitle is 20 points and 2009, I was given a task
 to implement a decal system
Bullets are blue
 So I researched what spacing, 2 points doing & after
They have 110% line other games are before
 Quick 2bullets in the form of a paragraph are harder to
Longer min review on shooting a bullet against a wall
maximum recommended number of lines per slide
(seven).

A Wall with 4 Verts

 Bullets are blue
 They have 110% line spacing, 2 points before & after
(seven).

Bullet Hits Here

(seven).

Want to text a create a Heading
Edit thisDrawto Dent Texture

(seven).

But this text to create a Heading
Edit How?

 Draw this texture points
This subtitle is 20 at the collision point

 To draw a texture, we need a mesh
Longer bullets in the form of a paragraph are harder to
 So let’s drawis insufficient line spacing. This is the
read if there a textured rectangle mesh
 But how can we generate the rectangle mesh that
maximum recommended number of lines per slide fits?
(seven).

Find Smallest Mesh Patch Covering It

(seven).

Duplicate the Mesh Patch

(seven).

And Draw

(seven).

Two Traditional Solutions

 This subtitle is 20 points resolution of underlying
1. (very easy) Increase the
geometry
2. They have 110% line spacing, 2 points before & after
 (not so easy) Magically calculate correct UV for each
verts
(seven).

1. Wall with Many Verts

(seven).

2. Calculate to create a
Edit this textCorrect UVsHeading

 (-4.5, -3.2)
Bullets are blue (3.4, -3.2)
(0, 0)
(1, 1)
(seven). 4)
(-4.5,
(3.4, 4)

Still this text to
Edit Problems create a Heading

 This subtitle is resolution of underlying geometry
1. Increase the 20 points
– Slower blue
 Bullets areto iterate
– More memory foot print
2. Longer bullets in the area = tooparagraph are harder to
 Wasted rasterized form of a much overdraw
– Edge of textures must be transparent
– Wasted rasterized area = too much overdraw
– UV calculation is tricky with complex geometries
(seven).

UV Calculation create a Heading
Edit this text to is Not Easy

 How subtitleyou points
 This would is 20
 calculate decals UVs
Bullets are blue
 from this statue? line spacing, 2 points before & after
They have 110%
(seven).

Brilliant text to
Edit this Idea? create a Heading

 So you would 20 points
This subtitle isthink we made Screen Space Decal to
 solve theseblue
Bullets are problems?
(seven).

Brilliant text to

 solve theseblue
NO.
(seven).

Brilliant text to

 solve theseblue
NO.
 The old way was simply too hard for me….
(seven).
 But SSD ended up solving these problems. 

Screen Space Decals a Heading
Edit this text to create(SSD)

 Similar techniques were
This subtitle is 20 points introduced by other developers
 in the recent years
Bullets are blue
  Deferred 110% line spacing, 2 points before & after
They haveDecals (Jan Krassnigg, 2010)
 Volume Decals (Emil Persson, 2011)
 SSD was developed independently, but the
implementation details is very similar
 So a quick review
(seven).
 More on howlook like this
 Sub bullets we used SSD and solved the problems
with SSD

SSDs in text to create
Edit this Space Marine a Heading

Not just for FX
 It's literally used everywhere:
 Blood splat on the wall or ground
 They havedecoration spacing, 2 points before & after
 Stone wall
110% line
 Longermark on concrete slate of a paragraph are harder to
 Burnt bullets in the form
 Ork there
read ifpainting is insufficient line spacing. This is the
 Rubble piles on the ground
 Bullet holes
(seven). damage
 Explosion
 ......and list goes on like this
 Sub bullets look
 Yup, environment artists loved it!

Edit This slide hasaa 16:9 media
this text to create Heading window
SSD ON
(seven).

SSD OFF
(seven).

Implementation Details

1. Draw underlying geometries onto scene
 Bullets are blue box
2. Rasterize a SSD
3. Read the scene depth for each pixel
4. Calculate 3D position from the depth
5. read if there is insufficient line spacing. This is the
If this position is outside of the SSD box, reject
6. maximum recommended number of decal per slide
Otherwise, draw the pixel with the lines texture
(seven).

Edit This slide hasaa 16:9Scene
this text toGiven This media
create Heading window
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Edit This slideWant Heading
this text to create aato Draw This
We has 16:9 media window
(seven).

Edit This slide underlyingmedia window
this text to create aa 16:9 geometries
1. draw has Heading
(seven).

Edit This slide hasaa 16:9SSD Box
2. rasterizer a media window
this text to create Heading

(seven).

Edit This slide hasaa 16:9SSD Box
2. rasterizer a media window

 They have 110%not this!
No line spacing, 2 points before & after
 Longer bullets in want to use it as a
We the form of a paragraph are harder to
projection box
(seven).

Edit3. read to create aa 16:9 for each pixel
This slide has depth media window
this text scene Heading

(seven).

4. calculate 3D create a Heading
Edit this text toposition from depth

float2 screenPosition = clipPosition.xy / clipPosition.w;
float2 depth_uv = screenPosition * float2(0.5f, -0.5f)
+ float2(0.5f, 0.5f);
depth_uv += ScreenDimension.zw;
Half-pixel Offset Basically
float sceneDepth = tex2D(DepthMap, depth_uv).r;
read if there is insufficient line spacing. This
is the
float4 scenePosView = float4(clipPosition.xy * sceneDepth
/ (Deproject.xy * clipPosition.w), -depth, 1);
(seven).
Deproject.X = ProjectionMatrix.M11;
Deproject.Y = ProjectionMatrix.M22;

Edit Thisif outside a 16:9 media window
this text to create a of SSD box, reject
5. slide has Heading
 This subtitle is 20 points OUTSIDE
 Bullets are blue INSIDE
OUTSIDE
(seven).

5. if this text to create Heading
Edit outside of the SSDabox, reject

• Simply transform the position
 This subtitle is 20 points to object space
• Then anything bigger than 0.5 is outside
position = mul(scenePosView, InvWorldView);
clip(0.5f - abs(position.xyz));
(seven).

Edit This6. to create aa 16:9 media window
this text Otherwise, draw decal
slide has Heading
// Decal Texture UV
(seven). float2 uv = position.xz;
 Sub bullets look like this += 0.5f;
uv

this text Now Lighting is Free
Edit This slide hasaa 16:9 media window
to create Heading

(seven).
Without SSD

this text Now Lighting is Free
to create Heading

(seven).
With SSD

thisandto create Heading is same
text combiner pass

(seven).

Mix-n-Match

 Artists can choose not to
This subtitle is 20 points draw decals either in Gbuffer
 or combiner pass
Bullets are blue
 Another free gift from spacing, 2 points before & after
They have 110% line light-prepass renderer
(seven).

this text to Gbuffer and Combiner
Both create Heading

(seven).

Edit This slide hasaa Gbuffer
Only 16:9 media
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this text to create Combiner
Only Heading
(seven).

More Examples (both)

(seven).

More Examples (GBuffer)

(seven).

More Examples (Combiner)

(seven).

Artist Control

 Artists make *.ssdecal file,
 which is are blue
Bullets just an XML
 In level editor, artists can
drag and drop any SSD
 From there, it’s
WYSIWYG & tweakable
per instance
(seven).

Problems & to Solutions
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1. Alpha Blending
 Bullets are Objects
2. Dynamic blue
3. Side Stretching
4. Clipped Decals
5. read if there is insufficient line spacing. This is the
Performance
(seven).

1. Alpha text to create a Heading
Edit this Blending(Normal)

•
 Transparent objects in combiner pass are fine
This subtitle is 20 points
•
 Transparent objects in Gbuffer are NOT
Bullets are blue
 – Originally 110% line spacing, 2 points before & after
They have just alpha test
– Later
 Longer enabled withthe form of a paragraph are harder to
bullets in Best Fit Normal by Crytek
– 3 months later, found a bug in our implementation of Best Fit
Normal: just same as our old normal buffer
maximum recommended numbernormal blending. So we are
– Artists never complained about weird
of lines per slide
(seven). it
still doing
– Mathematically wrong,this whatever
 Sub bullets look like but

1. Alpha text to create a Heading
Edit this Blending(Spec Power)

•
 Alpha channel of points
This subtitle is 20Gbuffer is specular power
•
 Cannot simply use normal alpha points before & after
They have 110% line spacing, 2 blending
 – alpha output from SSD shader
Longer bullets in the form ofisaused for RGB(normal) blending
paragraph are harder to
– Solution: Blend Factor!
maximum recommended =number of lines per slide
AlphaBlendFunction BlendFunction.Add;
AlphaSourceBlend
(seven). = Blend.BlendFactor;
AlphaDestinationBlend = Blend.InverseSourceAlpha;
 Sub bullets look like this = ssd.SpecularPower / 255.0f;
BlendFactor

1. Alpha Bleding(Spec Power)

(seven).


(seven). Power = 128


 Bullets are blue Power = 40
(seven). Power = 128

Edit This slideDynamic Objectswindow
2. has Heading
this text to create aa 16:9 media

(seven).

2. Dynamic Objects

•
 We subtitle attached the
Thiscould’ve is 20 points decal on moving objects
•
 But skinned mesh(e.g, ork arms) is still a problem
Bullets are blue
•
 So we simply didn’t draw any 2 points dynamic objects
They have 110% line spacing,decals onbefore & after
•
 Used a simple stencil buffer a paragraph
Longer bullets in the form of technique are harder to
(seven).

this text to create Heading Stencil
window
(seven).

Edit This slide hasaa Stretching
this text to3. SideHeading
create 16:9 media window
(seven).

3. Side Stretching

•
 Happens when SSD box’s
This subtitle is 20 points projection surface is not
 completely blue of underlying geometry
Bullets are inside

• They have 110% line spacing, 2 points before & after
Tried different ways

• Longer bulletsdoing rejectiona paragraph are harder to
But ended up in the form of based on the angle
read if there is insufficient box and underlying normal
difference between decal line spacing. This is the
from GBuffer
(seven).

Edit This slide hasaa Stretching
this text to3. SideHeading
create 16:9 media window
 Bullets are blue 90 degree
(seven).

3. Side Stretching

 Anything above this
 degree are blue
Bullets will be clipped

 180 degree means no
They have 110% line spacing, 2 points before & after
 clippingbullets in the form of a paragraph are harder to
Longer based on angle
 We found 60isdegree
read if there insufficient line spacing. This is the
works generally great number of lines per slide
maximum recommended
(seven).

3. Side Stretching

 This subtitle orientation In Vertex Shader:
1. Find box’s is 20 points
output.Orientation = normalize(WorldView[1].xyz);
2. gNormalThreashold is cos(degree)
3. maximum recommended number of lines per slide
Read GBufferNormal and clip in Pixel Shader
(seven). normal = DecodeGBufferNormal( tex2D(
float3
GNormalMap, depth_uv ) );
clip(dot(normal, orientation) - gNormalThreshold);

3. Side Stretching

•
 Alternatives is tried instead of hard clip
This subtitle we20 points
 Bullets arefade away based on angle between box orientation and
– smoothly blue
 vertex normal: looks horrible on “round” pipes
They have 110% line spacing, 2 points before & after
 – smoothly fade in the form of a paragraph are harder to
Longer bullets away based on angle between box orientation and
Gbuffer normal
• makes everything a bit too faint for existing arts
• With noisy gbuffer, artists liked hard clip more
(seven).
• Still worth trying for your games

4. Clipped Decals

•
 Doesn’t happen often environment decals
 Bullets decals carefully placed for performance reason
– Thin are blue

• They have 110% line spacing, 2 points before & after
Happens often with big FX explosion craters
 Longer bullets is insideformdecal box
– When camera in the of a of a paragraph are harder to
– No rasterization
(seven).

this text4. Clipped Decal (OK)
to create Heading

(seven).

this text to create Heading (BAD)
4. Clipped Decal

(seven).

4. Clipped Decals(Solution)

•
 When camera 20 points
This subtitle is is colliding with a decal

• Bullets are blue
We draw backface with flipped z-test, instead
• Bad for Performance
– No Hi-Z 
– But mostly problem with FX number we have an slide
maximum recommended decals andof lines per“amazing” way
of solving this (see next slides)
(seven).

Edit This slide hasaa (Drawing Backface)
4. this text to create Heading
Clipped Decal 16:9 media window
(seven).

5. Performance

•
 Avoid rasterizing points
This subtitle is 20pixels that will be rejected

• Bullets are blue early-Z with flipped Z-test
Avoid turning off
• So basically make decals very thin
– Environmental Decals are easy to solve
– FX Decals are not so easy
• (seven). Space Marine always runs at 30+ FPS
As a result,
except bullets look Decals go crazy 
 Sub when FX like this

5. Performance
Longer bullets in the form of a paragraph are harder to
(seven).
Two Sub bulletsdrawing this
 ways of look like this

5. Performance
(seven).
Thick bullets look like this
 Sub

5. Performance
(seven).
AndSub bullets look like this
 Thin

5. Performance
(seven).
PS Operations Wasted

5. Performance
 This subtitle is 20 points of Orks throw explosive stuff
A lot
(seven).

5. Performance
Which leaves large decals like this
(seven).

5. Performance
Sometimes 5 of them
 They have 110% line spacing, 2 points together after
stacked before &
(seven).

5. Performance
Sometimes 5 of them
 They have 110% line spacing, 2 points together after
stacked before &
read if there is insufficient line spacing. This is the passes
Almost 5 fullscreen
= only time we go down to
maximum recommended number FPS 25 of lines per slide
(seven).
Our Solution?

5. Performance
 This subtitle is 20 points THIS!
(seven).

5. Performance
 Bullets are blue So much overlay!
 They have 110% line spacing, 2 pointsSo many particles!
before & after
(seven).

5. Performance
before & after
don’t even notice it’s slow!
(seven).

5. Performance
before & after
don’t even notice it’s slow!
(seven). Was not intentional,
but saved us 

Special text to
Edit thisThanks create a Heading

•
 Relic Entertainment for allowing me to present this

• Bullets Marine rendering programmers
Space are blue
• Space Marine artists for producing amazing content and
 Longer bulletsdo more work! a paragraph are harder to
pushing us to in the form of
(seven).

References

• ENGEL, W. 2009, Designing
 This subtitle is 20 points a Renderer for Multiple Lights –
 The Light Pre-Pass Renderer. In ShaderX7: Advanced
Bullets are blue
Rendering Techniques, Charles River Media
• KAPLANYAN A. 2010, CryEngine 3: Reaching the Speed of
Light, Siggraph 2011
• KRASSNIGG, J. 2010. A Deferred Decallines per slide
maximum recommended number of Rendering
Technique. In Game Engine Gems 1, Jones and Barlett
(seven).
• PERSSON, E.look like this Decal. In GPU Pro 2, A K Peters
 Sub bullets 2011. Volume

Got this text to
Edit Questions?create a Heading

•
 More info on Space Marine rendering engine:
http://www.popekim.com/2011/11/slides-rendering-
tech-of-space-marine.html
• read if there is insufficient line spacing. This is the
Twitter: @BlindRenderer
• E-mail: blindrenderer@gmail.com
(seven).

(seven).

Screen Space Decals in Warhammer 40,000: Space Marine

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Screen Space Decals in Warhammer 40,000: Space Marine