General-purpose programming on GPU

How gaming brought us GPUs

Giuseppe Bilotta, Eugenio Rustico, Alexis Hérault

DMI — Università di Catania
Sezione di Catania — INGV

Evolution of video games

Games evolved with:

• more sophisticated gameplay
• more complex graphics
• shift to the third dimension
• more realistic game physics

Factors:

• better software
• better hardware

Software trick example: 'fast inverse square root'

float rsqrt(float x)
{
    float h = x/2;
    int i =  *(int*)&x;
    i = 0x5f3759df - (i>>1);
    x = *(float*)&i;
    return x*(1.5f - h*x*x); /* newton */
}

Hardware factors:

• faster CPUs
• more disk space, faster disks
• more and faster memory
• dedicated video hardware

Evolution of Video Cards

CGA (Color Graphics Adapter), 1981:

• 640x200, monochrome
• 320x200, 4 colors
• text modes, 16 colors
• (except for tricks)

EGA (Enhanced Graphics Adapter), 1984:

• 640x350, 16 colors palette (from 64 total colors, 2 bits per color per pixel)

VGA (Video Graphics Array), 1987:

• 6 bits per color per pixel: 262,144 different colors
• 256 colors programmable palette
• standard modes:
  • 640x480, 16 colors palette (from the 256)
  • 320x200, 256 colors
• first fully programmable video adapter, could be pushed to
  • 800 columns
  • 600 rows

IBM 8514, 1987:

• 1024x768, 256 colors, interlaced
• first 'professional' consumer device that accelerated basic 2D drawings:
  • line draw
  • color fill
  • 'bit blit' (pixel block combination with AND, OR, XOR).

IBM XGA, 1990:

• 800x600, 16-bit color (65,536 hues)
• 1024x768, 256-color palette

Mid-90's: Graphical User Interfaces (Windows, basically) become commonplace on consumer PCs. They benefit from hardware-accelerated 2D graphics. Leading companies: S3, Matrox, ATI.

Games and gamers wanted 3D graphics!

Auxiliary cards are born to handle scene rendering. Primary example: 3Dfx Voodoo. Programs must be written specifically to use it, but the quality justifies the effort (commercially, too).

Birth of GPUs

1990s. State of the art for professional (not consumer) 3D graphics: SGI, with hardware programmable using a specific API called IrisGL.

Competition from Sun, HP, IBM leads to an open subset: OpenGL.

OpenGL defines a set of (standard) functions to describe 2D and 3D 'scenes'. The API can be used to draw points, lines, polygons, set the viewer and light sources position, define colouring and textures.

OpenGL: cross-platform specification. DirectX/Direct3D: Microsoft Windows proprietary specification, specific for games. Advanced features include vertex and fragment shading: manipulate single 3D vertices or 2D pixels. These features are later included in OpenGL 2.0 too.

Video cards can support subsets of these APIs in hardware, the rest is software-emulated (and runs on the CPU).

Hardware support for 3D graphics acceleration leads to GPU (Graphic Processing Unit): computing processors that take care of the complex rendering operation, while the CPU takes care of AI, player control, physics engine, etc.