Image Synthesis
GP-GPU
computer graphics & visualization
Graphics hardware
• Current performace – PlayStation 3
• CPU: Cell Prozessor (3,2 GHz)
– 512 kB L2-Cache
– ~200 GFLOP/s
• GPU (Graphics Processing Unit)
– Nvidia RSX Reality Synthesizer (550 MHz, ~300
MTransistors
– ~ 1,8 TFLOP/s
– ~ 20 GPixels/s
– ~ 2 GTriangles/s
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Graphics hardware - history
• 80: simple rasterization
– Windows, lines, polygons, text-fonts
• 90-95: „Geometry-Engines“ only on High-End-Workstations
– e.g. SGI O2 vs. Indigo2)
• 95: new rasterization functionality
– Realism by texturing, e.g: SGI Infinite Reality
• 98: Geometry processor (T&L) on PC-Graphics
• 2000: PC-Graphics achieves similar performance to High-End-Workstations
– 3D is becoming standard in Aldi-PC
• 2001: PC-Graphics offers new functionality
– Multitextures, Vertex- and Pixel-Shader
• 2002: DirectX Level 9.0 Hardware
– High Level Shader Languages
• 2006: DirectX Level 10.0 Hardware
– Geometry – Shader
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Trends in graphics hardware
Number of transistors doubles every 6 months
Advances in performance and functionality
Transistors (Mi)
300
150
60
ATI R520
GeForceFX / ATI Radeon 9800
50
40
GeForce3 (57M) R200 (60M)
30
20
Riva 128 (3M)
10
0
9/97 3/98 9/98 3/99 9/99 3/00 9/00 3/01
9/02
Time (month/year)
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Trends in graphics hardware
• Grows faster than Moore‘s law predicts
Performance
Graphics
CPU
Network
Time
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Parallel graphics hardware
• Graphics hardware has always been parallel
– Internal on chip or board
• Multiple rasterizer serve one frame buffer
– Multi-Pipe
• Multiple graphics cards in one system for one or multiple
displays
• Multiple geometry engines
– Distributed graphics
• Multiple knots in a connected cluster with one or
multiple cards serve one or multiple displays driven by
one application
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Graphics architectures
• State-of-the-Art GPUs
– Highly parallel stream architecture
• Stream of vertices/fragments is processed
• Pipelined and SIMD parallel processing
– SIMD: single set of instructions on multiple stream elements
– Specifies new rendering pipeline
• Additional stages a vertex or a fragment is passing
through
– Specifies new (vendor specific) OpenGL extensions
– Allows for new classes of algorithms
– Eventually makes programs platform dependent
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Graphics architectures
State-of-the-Art GPUs (G80)
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Graphics architectures
• State-of-the-Art GPUs
–
–
–
–
–
Multiple (texture) render targets
Up to 2GB video memory
Floating point textures (4 x 32 Bit)
Internal computations in float /double precision
Z-cull: discards fragments (before entering the pixel
pipelines) that will fail the depth test
– Dynamic flow control: per-vertex/geometry/fragment
specific operations (if then else)
– PCIe: serial, pont2point protocol, dual channels to allow
for bandwidth in both directions (upload/download)
– Fix fragment-to-pixel bound, i.e. a fragment (XY) can not
be written to a pixel (X´Y´)
• no scattering (at least not in DX/GL)– only gathering
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Graphics architectures
State-of-the-Art programmable GPUs
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Graphics architectures
State-of-the-Art programmable GPUs
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
GP-GPU Water
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Programmable graphics hardware
Displacement mapping
Simulation generates
height field texture
static grid
water surface
Displacer
Rendering
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Programmable graphics hardware
• GPU memory objects
– Semantics can be specified for chunk of memory
– Memory object can be a texture, a vertex array, a frame
buffer object
• What was a texture render target in the current pass becomes
a vertex array in the upcoming pass
– Texture elements can be interpreted as vertex attributes
without any copying operations (not in OpenGL)
– Same effect can be achieved with vertex texture fetch,
but this fetch actually slows down performance
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Programmable graphics hardware
• Example
– Computation of height values u at vertices of a 2D grid
y
Pi-1j+1 Pij+1 Pi+1j+1
h
Pi-1j Pij
Pi+1j
Pi-1j-1 Pij-1 Pi+1j-1
h
x
2
2
2
2

 t
c

t
4
c

t
t 1
t
t
t
t
t 1


uij 
u

u

u

u

2

u

u
i 1 j
i 1 j
ij 1
ij 1
ij
2

 ij
h2
h




– Starting with an initial distribution, compute evolution
over time t
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Programmable graphics hardware
Algorithm:
– Load initial height values (NxxNy) as 2D texture (sGridPrev, sGrid)
– Upload fragment shader (render to sGridNew):
void PerPixelSim (
float2 fragpos: TEXCOORD0, out height : COLOR0) {
centerPrev = tex2D(sGridPrev, fragpos);
float2 leftIndex = float2(-1.0/TexSize, 0.0);
left = tex2D(sGrid, fragpos + leftIndex);
// same for right, upper, lower, center
height = f(left, right, upper, lower, center, centerPrev);
}
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Programmable graphics hardware
Algorithm contd.:
(0,1)
(1,1)
– Simulation:
• Render a Quad that covers Nx x Ny pixels
with appropriate texture coords.
– Nx x Ny fragments will be generated
– Data parallel execution of fragments
(texCoord = 0,0)
(1,0)
– Swizzle texture identifiers
• sGridPrev = sGrid, sGrid = sGridNew; sGridNew = sGrdPrev
– Display height field in texture sGrid
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Programmable graphics hardware
Algorithm contd.:
– Display:
• Upload fragment shader (render to color buffer):
void PerPixelRefract (
float2 fragpos: TEXCOORD0, out color : COLOR0) {
tangent = float3(1.0, 0.0, tex2D(sGrid, fragpos + rightIndex).r tex2D(sGrid, fragpos).r;
binormal = float3(0.0, 1.0, tex2D(sGrid, fragpos + upper).r tex2D(sGrid, fragpos).r);
normal = normalize(cross(tangent, binormal));
refract = f(normal, refractionIndex);
color = tex2D(sBackground, fragpos + refract); }
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
GPGPU Particle Tracing
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
GPU Partikelverfolgung
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
GPU Partikelverfolgung
Eingabe
Strom
Input
Assembler
Vertex
Shader
Rasterizer
Ausgabe
Strom
Output
Merger
Pixel
Shader
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization
Programmable graphics hardware
Demonstration
Image Synthesis – WS 07/08
Dr. Jens Krüger – Computer Graphics and Visualization Group
computer graphics & visualization