Chapter 12 Interactive Graphics ChihKuo Yeh Interactive Graphics

Chapter 12 Interactive Graphics Chih-Kuo Yeh

Interactive Graphics

Picking Direct Manipulation Demo

Object Picking by Ray Tracing Object 1 p 1 COP Center of Projection Window Coordinates Object 2 p 2

Open. GL Geometric Pipline Vertex Coordinates x, y, z, w Object Coordinates Modelview Matrix Modelview Transformation Eye Coordinates Projection Matrix Projection Transformation Clip Coordinates Perspective Division Device Coordinates Viewport Transformation Part of Open. GL State Viewport Transformation Window Coordinates x, y

Open. GL solution Selection Feedback Application Model API Output Devices Application Program Graphics System Function Calls or Protocol Data Input Devices

Selection

planets. cpp

The Basic Steps Process. Selection gl. Select. Buffer(…) gl. Matrix. Mode(GL_PROJECTION) gl. Push. Matrix() Change render mode gl. Matrix. Mode(GL_PROJECTION) gl. Pop. Matrix()

The Basic Steps Change render mode gl. Render. Mode(GL_SELECT ) glu. Pick. Matrix(…) Render. Scene() gl. Render. Mode(GL_RENDER )

The Basic Steps Render. Scene gl. Init. Names() gl. Push. Name() gl. Load. Name(…) Draw your object 1 gl. Load. Name(…) Draw your object 2

Selection Mode GLint gl. Render. Mode(GLenum mode); Mode = 1. GL_RENDER (the default) 2. GL_SELECT GL_RENDER 3. GL_FEEDBAC 1 zmin gl. Render. Mode() GL_SELECT zmax Yellow Cube gl. Render. Mode(GL_RENDER) returns the number of hits while in SELECT mode

Picking void glu. Pick. Matrix(GLdouble x, GLdouble y, GLdouble width, GLdouble height, GLint viewport[4]); gl. Get. Integerv(GL_VIEWPORT, viewport); glu. Pick. Matrix(x. Pos, viewport[3] – y. Pos + viewport[1], 2, 2, viewport);

Picking in Open. GL Perspective View Volume Canonical View Volume Projection Transform Screen Coordinates Pick Matrix Transform

The Hit Record Each hit record consists of four items, in order. 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. 1.

Selection Buffer

planets. cpp void Render. Scene(void) { // Clear the window with current clearing color gl. Clear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT // Save the matrix state and do the rotations gl. Matrix. Mode(GL_MODELVIEW); gl. Push. Matrix(); // Translate the whole scene out and into view gl. Translatef(0. 0 f, -300. 0 f); // Initialize the names stack gl. Init. Names();

void Mouse. Callback(int button, int state, int x, int y) { if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN Process. Selection(x, y); }

Process. Selection(int x. Pos, int y. Pos) void Process. Selection(int x. Pos, int y. Pos) { GLfloat f. Aspect; // Space for selection buffer static GLuint select. Buff[BUFFER_LENGTH]; // Hit counter and viewport storage GLint hits, viewport[4]; // Setup selection buffer gl. Select. Buffer(BUFFER_LENGTH, select. Buff);

// Get the viewport gl. Get. Integerv(GL_VIEWPORT, viewport); // Switch to projection and save the matrix gl. Matrix. Mode(GL_PROJECTION); gl. Push. Matrix(); // Change render mode gl. Render. Mode(GL_SELECT);

gl. Load. Identity(); glu. Pick. Matrix(x. Pos, viewport[3] - y. Pos + viewport[1], 2, 2, viewport); // Apply perspective matrix f. Aspect = (float)viewport[2] / (float)viewport[3]; glu. Perspective(45. 0 f, f. Aspect, 1. 0, 425. 0); // Draw the scene Render. Scene(); // Collect the hits = gl. Render. Mode(GL_RENDER);

GLuint n. Err = gl. Get. Error(); // If a single hit occurred, display the info. if(hits == 1) Process. Planet(select. Buff[3]); else glut. Set. Window. Title("Nothing was clicked on!"); // Restore the projection matrix gl. Matrix. Mode(GL_PROJECTION); gl. Pop. Matrix(); // Go back to modelview for normal rendering gl. Matrix. Mode(GL_MODELVIEW);

Hierarchical Picking

Hierarchical Picking

Moons. cpp

Selection Buffer Set up Pick Buffer Selection Buffer: user specified intege gl. Select. Buffer( int size, int *p. Buffer );

Name Stack Set up Pick Buffer Initialize Name Stack stack pointer gl. Render. Mode( GL_SELECT ); gl. Init. Names();

Pick Volume Set up Pick Buffer Initialize Name Stack Specify a Pick Volume glu. Pick. Matrix( x, y, 5. 0, viewport );

Fill Selection Buffer Set up Pick Buffer Initialize Name Stack Specify a Pick Volume Draw Object with IDs gl. Push. Name(100 ); gl. Draw. Red. Rect(); 1 0 0 100

Fill Selection Buffer Set up Pick Buffer Initialize Name Stack Specify a Pick Volume Draw Object with IDs gl. Push. Name(200 ); gl. Draw. Green. Rec t(); 1 0 0 100 200

Fill Selection Buffer Set up Pick Buffer Initialize Name Stack Specify a Pick Volume Draw Object with IDs gl. Push. Name(300 ); gl. Draw. Blue. Rect() ; 1 0 0 100 200

Post Processing Set up Pick Buffer Initialize Name Stack Specify a Pick Volume Draw Object with IDs Post Processing g. Render. Mode( GL_RENDER ); Do anything you want !!!

Feedback

select. cpp

The Basic Steps Process. Selection gl. Select. Buffer(…) gl. Matrix. Mode(GL_PROJECTION) gl. Push. Matrix() Change render mode gl. Matrix. Mode(GL_PROJECTION) gl. Pop. Matrix()

The Basic Steps Change render mode gl. Render. Mode(GL_SELECT ) glu. Pick. Matrix(…) Render. Scene() gl. Render. Mode(GL_RENDER )

The Basic Steps Render. Scene gl. Init. Names() gl. Push. Name() gl. Load. Name(…) gl. Pass. Through(…) Draw your object 1 gl. Load. Name(…)

The Basic Steps Make. Selection gl. Feedback. Buffer(…) gl. Render. Mode(GL_FEEDBACK ) Render. Scene() gl. Render. Mode(GL_RENDER ) Parse the feedback buffer

The Feedback Buffer void gl. Feedback. Buffer(GLsizei size, GLenum type, GLfloat *buffer);

Feedback Buffer Tokens

Feedback Buffer Memory GL_3 D 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 Make. Selection(int n. Choice) for detail