Chapter 12 Interactive Graphics Chih-Kuo Yeh

Direct Manipulation Demo

p1 COP Center of Projection p2 Window Coordinates Object 1 Object 2

Modelview Transformation Vertex Coordinates x, y, z, w Object Coordinates Eye Coordinates Clip Coordinates Device Coordinates Window Coordinates x,y Projection Transformation Perspective Division Viewport Transformation Modelview Matrix Projection Matrix Part of OpenGL State Viewport Transformation

 Selection  Feedback Application Model Application Program Graphics System Output Devices Input Devices API Function Calls or Protocol Data

glSelectBuffer(…) ProcessSelection glMatrixMode(GL_PROJECTION) glPushMatrix() glMatrixMode(GL_PROJECTION) glPopMatrix() Change render mode

glRenderMode(GL_SELECT ) glRenderMode(GL_RENDER ) RenderScene() gluPickMatrix(…) Change render mode

glInitNames() glPushName() glLoadName(…) RenderScene Draw your object 1 glLoadName(…) Draw your object 2

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

 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);

Perspective View Volume Canonical View Volume Projection Transform Pick Matrix Transform Screen Coordinates

 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.

void RenderScene(void) { // Clear the window with current clearing color glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Save the matrix state and do the rotations glMatrixMode(GL_MODELVIEW); glPushMatrix(); // Translate the whole scene out and into view glTranslatef(0.0f, 0.0f, f); // Initialize the names stack glInitNames(); glPushName(0); // Name and draw the Sun glColor3f(1.0f, 1.0f, 0.0f); glLoadName(SUN); DrawSphere(15.0f); // Draw Mercury glColor3f(0.5f, 0.0f, 0.0f); glPushMatrix(); glTranslatef(24.0f, 0.0f, 0.0f); glLoadName(MERCURY); DrawSphere(2.0f); glPopMatrix(); // Draw Venus glColor3f(0.5f, 0.5f, 1.0f); glPushMatrix(); glTranslatef(60.0f, 0.0f, 0.0f); glLoadName(VENUS); DrawSphere(4.0f); glPopMatrix(); // Draw the Earth glColor3f(0.0f, 0.0f, 1.0f); glPushMatrix(); glTranslatef(100.0f,0.0f,0.0f); glLoadName(EARTH); DrawSphere(8.0f); glPopMatrix(); // Draw Mars glColor3f(1.0f, 0.0f, 0.0f); glPushMatrix(); glTranslatef(150.0f, 0.0f, 0.0f); glLoadName(MARS); DrawSphere(4.0f); glPopMatrix(); // Restore the matrix state glPopMatrix();// Modelview matrix glutSwapBuffers(); }

void MouseCallback(int button, int state, int x, int y) { if(button == GLUT_LEFT_BUTTON && state == GLUT_DOWN) ProcessSelection(x, y); }

void ProcessSelection(int xPos, int yPos) { GLfloat fAspect; // Space for selection buffer static GLuint selectBuff[BUFFER_LENGTH]; // Hit counter and viewport storage GLint hits, viewport[4]; // Setup selection buffer glSelectBuffer(BUFFER_LENGTH, selectBuff);

// Get the viewport glGetIntegerv(GL_VIEWPORT, viewport); // Switch to projection and save the matrix glMatrixMode(GL_PROJECTION); glPushMatrix(); // Change render mode glRenderMode(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 scene RenderScene(); // Collect the hits hits = 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 matrix glMatrixMode(GL_PROJECTION); glPopMatrix(); // Go back to modelview for normal rendering glMatrixMode(GL_MODELVIEW);

glSelectBuffer( int size, int *pBuffer ); Set up Pick Buffer Selection Buffer: user specified integer array

stack pointer Set up Pick Buffer Initialize Name Stack glRenderMode( GL_SELECT ); glInitNames();

gluPickMatrix( x, y, 5.0, 5.0, viewport ); Initialize Name Stack Set up Pick Buffer Specify a Pick Volume

glPushName(100); Specify a Pick Volume Initialize Name Stack Set up Pick Buffer Draw Object with IDs glDrawRedRect();

glPushName(200); Specify a Pick Volume Draw Object with IDs Initialize Name Stack Set up Pick Buffer glDrawGreenRect();

Specify a Pick Volume Draw Object with IDs Initialize Name Stack Set up Pick Buffer glPushName(300); glDrawBlueRect();

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

glSelectBuffer(…) ProcessSelection glMatrixMode(GL_PROJECTION) glPushMatrix() glMatrixMode(GL_PROJECTION) glPopMatrix() Change render mode MakeSelection

glRenderMode(GL_SELECT ) glRenderMode(GL_RENDER ) RenderScene() gluPickMatrix(…) Change render mode

glInitNames() glPushName() RenderScene glLoadName(…) Draw your object 1 glPassThrough(…) glLoadName(…) Draw your object 2 glPassThrough(…)

glRenderMode(GL_FEEDBACK ) glRenderMode(GL_RENDER ) RenderScene() glFeedbackBuffer(…) MakeSelection Parse the feedback buffer

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

GL_3D type

[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