GAM532
DPS932 – Week 8
Texture Shadow Implementation
Depth Texture Shadows Basics
Render scene depth
from each light
Render Scene from
main camera for each
light
Compare depth from
light’s depth target
to each fragment
Binding Light Camera Values
struct Light {
float4 diffuse;
float4 specular;
float3 attenuation;
float3 spot;
};
Texture2D shadowTex : register(t0);
SamplerState shadowSamp : register(s0);
Render scene depth
from each light
Bind each shadow camera
to a depth target (no
color needed)
Bind each depth target
to a slot in the shader
Bridging the Gap
Main Camera’s View
Space
Rendering scene from
the main camera
Read from texture bound
to shadow camera
Shadow Camera’s
Clip-To-Texture
Space
Must find a way to
transform from one space
to the next
What We Need To Find
FragPos * InvLightMat
Main Camera’s
View Space
Fragment
Position
Shadow Camera’s
View Space
Fragment
Position
Main Camera’s
View Space
Fragment
Position
Main Camera’s
View Space Light
Transformation
Inverse
Inversion of Orthographic Matrices
| 0 1
| 0 0
| -1 0
| -8 9
0
1
0
3
0
0
0
1
|
|
|
|
Origin
Orthographic
Matrix
Inverse
Translation +
Identity
Transpose
Rotation Translation
|
|
|
|
|
|
|
|
1 0 0
0 1 0
0 0 1
8 -9 -3
0
0
0
1
|
|
|
|
Inverse
Translation
Matrix
*
0
1
0
0
0 -1 0 |
0 0 0 |
1 0 0 |
0 0 1 |
Inverse
Rotational
Matrix
=
| 0 0 -1 0 |
| 1 0 0 0 |
| 0 1 0 0 |
| -9 -3 -8 1 |
Inverse
Orthographic
Matrix
From View Space to Clip Space
struct Light {
float4x4 shadowProjection;
float4 diffuse;
float4 specular;
float3 attenuation;
float3 spot;
};
Texture2D shadowTex : register(t0);
SamplerState shadowSamp : register(s0);
Shadow Camera’s
View Space
Fragment
Position
Shadow Camera
Projection
Transformation
FragPos * shadowProjection
Clip Space To Texture Coordinate
Screen Coordinates
-1
[ 23 12 29 31 ]
[ x/w y/w z/w w/w]
[ 0.74 -0.39 0.94 ]
X
Y
Depth
-1
[ 0.74 -0.39 0.94 ]
1
1
U
V
Depth
[ x/2+0.5 y/2+0.5 z ]
0
[ 0.74 -0.39 0.94 1 ]
[ 0.87 0.31 0.94 ]
1
0
Shadow Camera’s
Clip Space
Fragment
Position
Screen
Coordinates of
Fragment with
Depth
1
Texture Coordinates
Texture
Coordinates of
Fragment with
Depth
Testing Depth
Yes
0.87
[ 0.87 0.31
0.94 ]
0.31
U
V
Depth
Texture
Coordinates of
Fragment with
Depth
Sample Depth
from Shadow
Texture
Is sampled depth
lower than the
calculated depth
of the fragment?
No
The light hit a
different object first,
shadow casted on
fragment, fragment is
not lit
The light hit the
surface of the object,
no shadow casted on
fragment, fragment is
lit
Adding All Lights Together
Each light contributes to an object
Shadows only block one light
Single object can project many shadows
+
+
=
Final Result
High Detail (texture limited)
Dynamically changing Shadow
Self Shadowing
Translucency effects easily added
Expensive
(re-render scene for each light)
Detail limited by texture size
Point lights are very
expensive to cast shadows from
(6 renders per light)
Shadow Texture Notes
Point lights require
up to 6 shadow
textures to map out
(don’t do it)
Point and spot lights
radiate light in many
directions
Directional lights
work in one direct
and require an
orthographic camera
Depth Fighting Shadow Acne
Floating point precision issue
0.94534 > 0.94522
0.945341458 > 0.945341456
0.945341458458??? > 0.945341458458???
Shadow Acne
No Acne
0.945341458458??? + 0.0000001
>
0.945341458458???
Alias Reduction
float2 poissonDisk[4] = {
float2(-0.94201624, -0.39906216),
float2(0.94558609, -0.76890725),
float2(-0.094184101, -0.92938870),
float2(0.34495938, 0.29387760)
);
for (int i=0; i<4; i++) {
if(texture2D(shadowTex, shadow.xy +
poissonDisk[i]/700.0).z<ShadowCoord.z-bias ){
visibility-=0.2;
}
}
Texture resolution
can cause aliasing
Sampling adjacent
texels and blending
can soften shadows
Graphics Section Complete
Audio Next…
To Do
• Begin work on your enhancement
• Begin work on OpenGL labs
• Prepare for Mid-term (for real this time, I’m not pushing back again)