Graphics Libraries

Presented By:Prachi Mishra

Contents

Overview

Common Graphics Libraries

PHIGS

Features of PHIGS

OpenGL

OpenGL Pipeline

Commands

Direct3D

How’s Direct3D Different?

Conclusion

References

03

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05

06

07

08

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14

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Overview

• Today 3D graphics tools provide new methods in engineering, medicine, entertainment and technology

• These are selected from exhaustive online research

• Incorrect selection can lead to undesired results

• A graphics library is a software interface to graphics hardware commonly called the APIs

• It provides a set of graphics commands and functions which can specify primitive geometric models and their attributes to digitize and display

Common Graphics Libraries

A graphics programmer is should be able to program in at least one of the following:

• OpenGL

• Direct3D

• PHIGS (Programmer's Hierarchical Interactive Graphics System)

• GKS (Graphics Kernel System)

PHIGS (Programmer's Hierarchical Interactive Graphics System)

• An API standard for rendering 3D computer graphics through 1980s

• Available as a standalone implementation like IBM’s GraPHIGS or Sun’s SunPHIGS

• Became a standard by 1990s ( ANSI and ISO)

• Supports only the most basic 3D graphics, including basic geometry and meshes

• A combination of features of PHIGS and power led to the rise of OpenGL

Features of PHIGS

• Included a scene graph which is a data structure for storing logical sequences

• Had a CSS (Centralized Structure Store) i.e. a database for storing primitives and their attributes

• CSSes were shared under workstations to give views

• Simple working:

Model built into CSSWorkstation created and opened Model connected

OpenGL (Open Graphics Library)

• Most widely adopted graphics API

• Easy to use, well documented

• Cross platform and cross language

• Everything is primitive (can accept only simple shapes and sizes)

• Largely built on C but can be used in most programming languages

OpenGL Graphics Pipeline

void display(void){

int x, y;//a. generate a random pointx = rand() % Width;y = rand() % Height;//b. specify a drawing color: redglColor3f(1, 0, 0);//c. specify to draw a pointglBegin(GL_POINTS);glVertex2i (x,y);glEnd();//d. start drawingglFlush();

}

Basic Commands for Drawing and Shape

void drawtriangle(float *v1, float *v2, float *v3){glBegin(GL_TRIANGLES);glVertex3fv(v1);glVertex3fv(v2);glVertex3fv(v3);glEnd();}

Commands for Transformation

glPushMatrix();glLoadIdentity ();glRotatef (alpha, 0.0, 0.0, 1.0);drawArm (O, A);glTranslatef (A[0], A[1], 0.0);glRotatef (beta, 0.0, 0.0, 1.0);glTranslatef (-A[0], -A[1], 0.0);drawArm (A, B);

glPopMatrix();

Viewing

static void reshape(int w, int h)

{

//a.specify modeling coordinates

glMatrixMode(GL_PROJECTION);

glLoadIdentity ();

glOrtho(left, right, bottom, top, new, far);}

Color and Lighting

• Different colors for different vertices of the model can be specified

• Light sources can be put to give different colors at different positions in the environment, so the model can have overall brightness, dull reflections, and/or shiny spots

• Lighting can be achieved by calculating the color of a pixel

• The normal of the pixel, the position of the viewer, and the colors and positions of the light sources inherently decide the lighting

Transparency

▪ Used for transparent objects by implementing transmission coefficients for overlapping objects

▪ A final pixel’s R,G or B value depends on the blending of the corresponding R, G, or B values of the pixels in the overlapping objects through the transmission coefficients: Iλ = a1Iλ1 + a2 Iλ2, where λ is R, G, or B; Iλ the blended color component, a1 the transmission coefficient of the pixel in the first object, and Iλ1 the color of the first object.

Direct3D

• Graphics API for Microsoft Windows

• Used to render 3D applications where performance is important like gaming environments

• Implemented on Windows family of operating systems

• Also on embedded versions of Xbox family of video game consoles

How’s Direct3D Different?

▪ Portability – OpenGL is cross platform while Direct3D is Windows centric

▪ User Functionality – Direct3D is 3D hardware interface while OpenGL is 3D rendering system that could be hardware accelerated

▪ Performance – Direct3D is more suitable when performance is considered because of lighter codes

▪ Users/Applications – OpenGL has always seen more number of users. Direct3D is mostly used for computer games

References

▪ http://www.opengl.org

▪ http://mohammadshakergtr.wordpress.com/

▪ http://graphics.wikia.com/wiki/Direct3D_vs._OpenGL

▪ http://slideshare.net/OpenGL_Basics

▪ https://ilias.fhv.at/goto_ilias_fhv_at_file_225344_download.html