Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex...

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Real-Time Rendering Graphics Programming

Transcript of Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex...

Page 1: Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex and fragment shaders Replace fixed functionality Shader: high-level language (C-like)

Real-Time Rendering

Graphics Programmingp g g

Page 2: Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex and fragment shaders Replace fixed functionality Shader: high-level language (C-like)

Graphics Libraries (APIs)

Give access to graphics hardware…D l ti (Wh t t H )Declarative (What, not How)

Describe the scene (e.g., scene graphs) SGI Open Inventor, SGI Performer, Renderman OpenSceneGraphRenderman, OpenSceneGraph…

Imperative (How, not What)Sequence of drawing commandsOpenGL, DirectX (Direct3D), PostscriptOpenGL, DirectX (Direct3D), PostscriptMore direct control

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Graphics Libraries (APIs)

Using a scene graph API…

ApplicationApplicationApplicationApplication

ScenegraphScenegraphScenegraphScenegraph

ApplicationApplicationApplicationApplication

Windows/LinuxWindows/LinuxWindows/LinuxWindows/Linux OpenGLOpenGLOpenGLOpenGL

ScenegraphScenegraphScenegraphScenegraph

Windows/LinuxWindows/LinuxWindows/LinuxWindows/Linux OpenGLOpenGLOpenGLOpenGL

HardwareHardwareHardwareHardware

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Graphics Libraries (APIs)

Using an immediate-mode API…

ApplicationApplicationApplicationApplication

GLUTGLUTGLUTGLUT

ApplicationApplicationApplicationApplication

Windows/LinuxWindows/LinuxWindows/LinuxWindows/Linux OpenGLOpenGLOpenGLOpenGL

GLUTGLUTGLUTGLUT

Windows/LinuxWindows/LinuxWindows/LinuxWindows/Linux OpenGLOpenGLOpenGLOpenGL

HardwareHardwareHardwareHardware

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Immediate vs. Retained

Immediate (OpenGL)Total control over renderingTotal control over rendering

traversal and data structures and formatsMany subroutine callsDriver cannot optimizeDriver cannot optimize

Retained (scene graph, display lists)Driver can optimize execution of display listsAPI can optimize traversal of scene graphAPI can optimize traversal of scene graph

for different platforms!T l i diffi lt t h

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Traversal is difficult to change

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The OpenGL Graphics System

Web site: www.opengl.orgO GL t d k d b SGIOpenGL trademark owned by SGI

More than 70 licenseesOpenGL is controlled by the “ARB”

Architecture Review BoardArchitecture Review BoardMembers: Compaq, IBM, Intel, Microsoft, SGI, Evans & Sutherland, HP, Sun, NVidia, ATI, AppleppMeeting notes on the Web

follow ARB decisions discussionsVienna University of Technology 6

follow ARB decisions, discussions, …

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A Short OpenGL Freshup

All primitives made up of vertices…

G O SGL POINTS

GL_LINESGL_LINES

GL_POLYGONGL_POLYGONGL LINE LOOPGL LINE LOOPGL LINE STRIPGL LINE STRIP

GL_POINTSGL_POINTS_ __ __ __ _

GL_TRIANGLESGL_TRIANGLES

GL QUAD STRIPGL QUAD STRIPGL TRIANGLE FANGL TRIANGLE FANGL TRIANGLE STRIPGL TRIANGLE STRIP

GL_QUADSGL_QUADS

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GL_QUAD_STRIPGL_QUAD_STRIP_ __ _GL_TRIANGLE_STRIPGL_TRIANGLE_STRIP

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A Short OpenGL Freshup

Shading: From wire frame to texture mappedFrom wire frame to texture mapped…

Wire frame (hidden line) flat shading

Gouraud Textured (Combination)

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Gouraud Textured (Combination)

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Short History of OpenGL1982 Silicon Graphics (SGI) incorporated1983 IRIS GL on IRIS 1000 terminal

(the predecessor to OpenGL)(the predecessor to OpenGL)1991 OpenGL ARB created1992 OpenGL 1.0 (June 30)1995 OpenGL 1 11995 OpenGL 1.11996 OpenGL specification made public1998 OpenGL 1.2

O G2000 OpenGL goes open source2001 OpenGL 1.32002 OpenGL 1.42002 OpenGL 1.42003 OpenGL 1.52004 OpenGL 2.0 (Shaders)2008 OpenGL 3 0 (Depreciation model)2008 OpenGL 3.0 (Depreciation model)2008 OpenGL 3.0 (Depreciation model)2009 OpenGL 3.2 (Geometry shaders)2010 O GL 4 0 (T l ti )

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2010 OpenGL 4.0 (Tesselation)

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Modern Graphics Pipeline

Application

Command

Geometry

Rasterization

TextureTexture

Fragment

Display

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OpenGL Programing Model

OpenGL is a state machineAll command change stateAll command change stateOnly glVertex causes action

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Page 13: Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex and fragment shaders Replace fixed functionality Shader: high-level language (C-like)

OpenGL Design Goals

Platform independent (unlike DirectX)Window-system dependent code separate (GLXWindow system dependent code separate (GLX, WGL)Implementations on Windows Linux MacOS BeImplementations on Windows, Linux, MacOS, Be, OS/2, Unix, …Language independent (bindings for C JavaLanguage independent (bindings for C, Java, Fortran, …)

Consistency (unlike DirectX 9)Consistency (unlike DirectX 9)Tightly written specificationConformance tests and required verificationNot too tight: not pixel exact

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Invariance across passes (for correct multipass)

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OpenGL Design Goals

Complete implementations (unlike DirectX 9)Missing hardware features emulated inMissing hardware features emulated in softwareSilent error recoverySilent error recovery

Clean interface (unlike DirectX 9)State machineMost states are orthogonal (i.e., don’t g ( ,influence each other, no side effects!)

Extensibility (unlike DirectX 9)Extensibility (unlike DirectX 9)Favors innovationN HW f t fi t il bl O GL!

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New HW features first available on OpenGL!

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More Goals

High qualityI t iti bilit (b t t )Intuitive usability (beauty counts)Good documentation (Programming Guide)( g g )Long life…

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OpenGL Problems

ExtensibilityDifferent extensions for different GPUsDifferent extensions for different GPUsHell for production code (games)

D i b ittDesign by committeeUnified extension interfaces take long timeVery slow to adopt non-GPU specific features (e.g., offscreen buffers)

Non-existent toolsetShading debuggers (but: gDebugger)g gg ( g gg )Performance tools (but: NVPerfKit)Mesh tools (already included in DirectX)

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Mesh tools (already included in DirectX)Mediocre driver support

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OpenGL Extensions

SGI maintains central registryC f ll d t dCarefully documented

Takes into account previous extensionsNew OpenGL version could be implemented by applying all extensionsby applying all extensions

A bit difficult to readRead overview, then “Additions to…”

Very stable processVery stable processExtensions are refined and improved…

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OpenGL Extension Categories

Proprietary: suffixed with vendore g SGIS texture lod NV fragment programe.g., SGIS_texture_lod, NV_fragment_program

EXT suffixI l t d b t l t 2 d ( ll NV AMD)Implemented by at least 2 vendors (usually NV,AMD)e.g. EXT_blend_func_separate

ARB suffixSpecification controlled by ARBp yARB_multitexture

1 x: no suffix1.x: no suffixRequired feature for version 1.x

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Page 20: Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex and fragment shaders Replace fixed functionality Shader: high-level language (C-like)

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Page 23: Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex and fragment shaders Replace fixed functionality Shader: high-level language (C-like)

Using Extensions

Get glext.h from www.opengl.orgCh k f t i il bilitCheck for extension availabilityAcquire function pointer(s) (only Win32)q p ( ) ( y )Easier: use glew or glee

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OpenGL 2.0

Main novelty: shading language GLSLV t d f t h dVertex and fragment shaders

Replace fixed functionalityShader: high-level language (C-like)O GL d i il d li k fOpenGL driver: compiler and linker for shadersVertex-, texture coordinates etc.: abstract input values to shader functionabstract input values to shader functionArbitrary calculations possible

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Requires DX9 (GeforceFX/6) cards

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OpenGL 3.0

Not much newV t A Obj tVertex Array Objects

Encapsulate VBO statesRGB framebuffersT tTexture arraysTransform feedbackExtensions: geometry shaders, instancing, ...D i ti h i !Depreciation mechanism!

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OpenGL 3.2

Geometry shaders

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Page 27: Real-Time Rendering Grappg ghics Programming · Main novelty: shading language GLSL Vt df thdVertex and fragment shaders Replace fixed functionality Shader: high-level language (C-like)

OpenGL 4.0/3.3

TesselationTi iTimer queriesDouble precision floating pointp g pEtc.O GL 3 3 f tibilit ith ldOpenGL 3.3: for compatibility with older hardware

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OpenGL ES

For embedded systemsR d d i t ti tReduced instruction setDevelopers love it pOpenGL 4.1 is backwards compatible with OpenGL ES!OpenGL ES!

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OpenGL Architecture

Symmetric geometry and image pathsO ti i d d t (“ th l”)Operations independent (“orthogonal”)

UnpackPixels

PixelOperations

ImageRasterization

PackTexture Fragment

Image

PackPixels

Memory Operations

Point, Line,Polygon

Rasterization

UnpackVertexes

VertexOperations

FrameBufferGeometry

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Rasterization

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Typical OpenGL Block Diagram

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They match!

Application

Command

Geometry

RasterizationRasterization

Texture

Fragment

Display

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Introduction to the OpenGL Shading Language (GLSL)web.engr.oregonstate.edu/~mjb/cs550/PDFs/Shaders.1pp.pdfmjb –August 9, 2020 5 Computer Graphics GLSL Variable Types attribute These

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