Open gles

OpenGL amp OpenGLES

Introduction to OpenGL

OpenGL (Open Graphics Library)[2] is a standard specification defining a cross-language cross-platform API for writing applications that produce 2D and 3D computer graphics

The interface consists of over 250 different function calls which can be used to draw complex three-dimensional scenes

OpenGL was developed by Silicon Graphics Inc (SGI) in 1992[3] and is widely used in CAD virtual reality scientific visualizationinformation visualization and flight simulation

It is also used in video gameswhere it competes with Direct3D on Microsoft Windows platforms

OpenGL is managed by a non-profit technology consortium the Khronos Group

Introduction to OpenGLES

OpenGL ES (OpenGL for Embedded Systems) is a subset of the OpenGL 3D graphics API designed for embedded devices such as mobile phones PDAs and video game consoles

It is defined and promoted by the Khronos Groupa graphics hardware and software industry consortium interested in open

APIs for graphics and multimedia

The following APIs will provide central understanding in OpenGL amp OpenGLES

1048577 glVertexPointer 1048577 glDrawElements 1048577 glColor 1048577 glClear 1048577 gluLookAt 1048577 glFrustum 1048577 glViewport

OpenGL ES offers two primary methods to facilitate drawing

glVertexPointer to specify a series of points or

vertices

glDrawElements to draw them using one of the

primitive shapes

glVertexPointer( Are we using (xy) or (xyz) in each point

3 each value is a float value in the buffer

GL10GL_FLOAT Between two points there is no space

0 pointer to the start of the buffer

mFVertexBuffer)

glVertexPointer API Definition

glVertexPointer takes native buffer rather than array floatsWe need to convert these java-based floats into an accceptable C-like native bufferWe use Javanio classes to convert float array into native buffer

javanioByteBuffer vbb = javanioByteBufferallocateDirect(3 3

4)vbborder(ByteOrdernativeOrder())javanioFloatBuffer mFVertexBuffer =

vbbasFloatBuffer()

glDrawElements API Definition

glDrawElements( type of shape

GL10GL_TRIANGLE_STRIP Number of indices

3 How big each index is

GL10GL_UNSIGNED_SHORT buffer containing the 3 indices

mIndexBuffer)

glColor

We use it to set the default color for the subsequent drawing that takes place

Set the current color glColor4f(10f 0 0 05f)

Where 4f refers to 4 arguments all are float

glClear

This method is used to erase the drawing surface we can reset not only the color but also the depth and the type of stencils used

GL_COLOR_BUFFER_BIT GL_DEPTH_BUFFER_BIT GL_STENCIL_BUFFER_BIT

Understanding OpenGL Camera and Coordinates

gluLookAt Controls the direction of the

camera

glFrustum Controls the viewing volume or zoom

glViewport Controls the size of the screen or the size of the camerarsquos ldquofilmrdquo

Y-axis

Frustrum

Z-axis

Point it up

height000

Near(3)

Far(7)

gluLookAt(gl 005 000 010)

location of the camera

Eye point

direction the camera is pointing

Look-at point

whether the camera is up down or slanted

Up vector

glFrustrumto specify the area of the scene that you are interested inThe area as bounded by a box also called the frustum or viewing volume

frustrum= far point - near point

In OpenGL you can imagine this box in one of two ways

Prespective projection Orthographic projection

Specifying a Frustum through glFrustum

calculate aspect ratio first

float ratio = (float) w hindicate that we want a perspective projection

glMatrixMode(GL10GL_PROJECTION)Specify the frustum the viewing volume

glglFrustumf( -ratio Left side of the viewing box

ratio right side of the viewing box

1 top of the viewing box

-1 bottom of the viewing box

3 how far is the front of the box from the camera

7) how far is the back of the box from the camera

glViewport

It is responsible for specifying the rectangular area on the screen onto which the viewing volume will be projected

glViewport(0 lower left x of the rectangle on the screen

0 lower left y of the rectangle on the screen

width width of the rectangle on the screen

height) height of the rectangle on the screen

The other classes in the package include

GLUThis utility class contains utilities that wrap the underlying OpenGL ES API in order to aggregate some common functionality

GLUtilsThis utility class contains Android-specific utilities that are built to make interacting with the OpenGL ES easier

MatrixThis is the transformation matrix that is essential for transformations such as scaling moving etc

VisibilityIt deals with the visibility aspects of OpenGL

such as what triangle meshes are visible on the screen GLDebugHelperA static utility class that allows you to

wrap the ldquoGLrdquoand ldquoEGLrdquo interfaces so that you can control logging errors additional checks etc

GLSurfaceViewEGLConfigChooserAn EGL tells

OpenGL the type of display characteristics GLSurfaceViewGLWrapperThis interface allows you to

wrap theldquoglrdquo interface so that you can intercept the OpenGL calls across the entire system

GLSurfaceViewRendererThis interface allows for derived classes to draw It allows GLSurfaceView to call draw when the surface has changed etc

public static interface GLSurfaceViewRenderervoid onDrawFrame(GL10 gl)void onSuraceChanged(GL10 gl int width int

height)void onSurfaceCreated(GL10 gl EGLConfig config)

onDrawFrame()- This is called to draw the current frameThe main drawing happens in this method onSurfaceCreated()-Whenever new surface is created this method is calledwe can also call a no of OpenGL APIrsquos such as dithering or depth controlonSurfaceChanged()-Whenever surface changes

such as width height of the window this method is called

Thank You