Chapter 12 Interactive Graphics

Chapter 12

Interactive Graphics

Chih-Kuo Yeh

Interactive Graphics

Picking

Direct Manipulation Demo

Object Picking by Ray Tracing

p1

COPCenter of Projection

p2

WindowCoordinates

Object 1Object 2

OpenGL Geometric Pipline

ModelviewTransformation

Vertex Coordinatesx, y, z, w

Object Coordinates

Eye Coordinates

Clip Coordinates

Device Coordinates

Window Coordinates x,y

ProjectionTransformation

PerspectiveDivision

ViewportTransformation

Modelview Matrix

Projection Matrix

Part of OpenGL State

ViewportTransformation

OpenGL solution

SelectionFeedback

ApplicationModel

ApplicationProgram

GraphicsSystem

OutputDevices

InputDevices

API

Function Callsor Protocol

Data

Selection

planets.cpp

The Basic Steps

glSelectBuffer(…)

ProcessSelection

glMatrixMode(GL_PROJECTION)

glPushMatrix()


glPopMatrix()

Change render mode

The Basic Steps

glRenderMode(GL_SELECT )

glRenderMode(GL_RENDER )

RenderScene()

gluPickMatrix(…)

Change render mode

The Basic Steps

glInitNames()

glPushName()

glLoadName(…)

RenderScene

Draw your object 1

glLoadName(…)

Draw your object 2

Selection Mode

GLint glRenderMode(GLenum mode);Mode = 1. GL_RENDER (the default)2. GL_SELECT3. GL_FEEDBAC

glRenderMode()

GL_RENDER

GL_SELECT

1

zmin

zmax

Yellow Cube

glRenderMode(GL_RENDER) returns the number of hits while in SELECT mode

Picking

void gluPickMatrix(GLdouble x, GLdouble y, GLdouble width, GLdouble height, GLint viewport[4]);

glGetIntegerv(GL_VIEWPORT, viewport);

gluPickMatrix(xPos, viewport[3] – yPos + viewport[1], 2,2, viewport);

Picking in OpenGL

y

xz

z

x

y

Plane z= -1

Plane z= +1

DOP

z

x

y

Perspective View Volume Canonical View Volume

Projection

TransformPick MatrixTransform

Screen Coordinates

The Hit Record

Each hit record consists of four items, in order.1. The number of names on the name stack when

the hit occurred.2. Both the minimum and maximum window-

coordinate z values 3. The contents of the name stack at the time of

the hit, with the bottommost element first.

Selection Buffer

planets.cpp

void RenderScene(void){

// Clear the window with current clearing colorglClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

// Save the matrix state and do the rotationsglMatrixMode(GL_MODELVIEW);glPushMatrix();

// Translate the whole scene out and into viewglTranslatef(0.0f, 0.0f, -300.0f);

// Initialize the names stackglInitNames();glPushName(0);

// Name and draw the SunglColor3f(1.0f, 1.0f, 0.0f);glLoadName(SUN);DrawSphere(15.0f);

// Draw MercuryglColor3f(0.5f, 0.0f, 0.0f);glPushMatrix();glTranslatef(24.0f, 0.0f, 0.0f);glLoadName(MERCURY);DrawSphere(2.0f);glPopMatrix();

// Draw VenusglColor3f(0.5f, 0.5f, 1.0f);glPushMatrix();glTranslatef(60.0f, 0.0f, 0.0f);glLoadName(VENUS);DrawSphere(4.0f);glPopMatrix();

// Draw the EarthglColor3f(0.0f, 0.0f, 1.0f);glPushMatrix();glTranslatef(100.0f,0.0f,0.0f);glLoadName(EARTH);DrawSphere(8.0f);glPopMatrix();

// Draw MarsglColor3f(1.0f, 0.0f, 0.0f);glPushMatrix();glTranslatef(150.0f, 0.0f, 0.0f);glLoadName(MARS);DrawSphere(4.0f);glPopMatrix();

// Restore the matrix stateglPopMatrix(); // Modelview matrix

glutSwapBuffers();}

void MouseCallback(int button, int state, int x, int y){

if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN)ProcessSelection(x, y);

}

ProcessSelection(int xPos, int yPos)

void ProcessSelection(int xPos, int yPos){

GLfloat fAspect;

// Space for selection bufferstatic GLuint selectBuff[BUFFER_LENGTH];

// Hit counter and viewport storageGLint hits, viewport[4];

// Setup selection bufferglSelectBuffer(BUFFER_LENGTH, selectBuff);

// Get the viewportglGetIntegerv(GL_VIEWPORT, viewport);

// Switch to projection and save the matrixglMatrixMode(GL_PROJECTION);glPushMatrix();

// Change render modeglRenderMode(GL_SELECT);

glLoadIdentity();gluPickMatrix(xPos, viewport[3] - yPos + viewport[1], 2,2, viewport);

// Apply perspective matrix fAspect = (float)viewport[2] / (float)viewport[3];gluPerspective(45.0f, fAspect, 1.0, 425.0);

// Draw the sceneRenderScene();

// Collect the hitshits = glRenderMode(GL_RENDER);

GLuint nErr = glGetError();// If a single hit occurred, display the info.if(hits == 1)

ProcessPlanet(selectBuff[3]);else

glutSetWindowTitle("Nothing was clicked on!");

// Restore the projection matrixglMatrixMode(GL_PROJECTION);glPopMatrix();

// Go back to modelview for normal renderingglMatrixMode(GL_MODELVIEW);

Hierarchical Picking

Hierarchical Picking

Moons.cpp

Selection Buffer

glSelectBuffer( int size, int *pBuffer );

Set up Pick Buffer

Selection Buffer: user specified integer array

Name Stack

stack pointer

Set up Pick Buffer

Initialize Name Stack

glRenderMode( GL_SELECT );glInitNames();

Pick Volume

gluPickMatrix( x, y, 5.0, 5.0, viewport );


Set up Pick Buffer

Specify a Pick Volume

Fill Selection Buffer

glPushName(100);1 0 0 100



Set up Pick Buffer

Draw Object with IDs

100

glDrawRedRect();


glPushName(200);1 0 0 100 2 0 0 100 200




Set up Pick Buffer

200100

glDrawGreenRect();


1 0 0 100 2 0 0 100 200

100200300




Set up Pick Buffer

glPushName(300);

glDrawBlueRect();

Post Processing

Do anything you want !!!




Set up Pick Buffer

Post Processing

gRenderMode( GL_RENDER );

Feedback

select.cpp

The Basic Steps

glSelectBuffer(…)

ProcessSelection


glPushMatrix()


glPopMatrix()

Change render mode

The Basic Steps

glRenderMode(GL_SELECT )


RenderScene()

gluPickMatrix(…)

Change render mode

The Basic Steps

glInitNames()

glPushName()

RenderScene

glLoadName(…)

Draw your object 1

glPassThrough(…)

glLoadName(…)

glPassThrough(…)

The Basic Steps

glRenderMode(GL_FEEDBACK )


RenderScene()

glFeedbackBuffer(…)

MakeSelection

Parse the feedback buffer

The Feedback Buffer

void glFeedbackBuffer(GLsizei size, GLenum type, GLfloat *buffer);

Feedback Buffer Tokens

Feedback Buffer Memory

GL_3D type

Feedback Buffer Memory

[0] GL_PASS_THROUGH_TOKEN[1] User defined name[2] GL_POLYGON_TOKEN[3] Number of vertices[4] x[5] y See MakeSelection(int nChoice) for detail

Documents

Chapter 12 Interactive Graphics