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CS 4204 Computer Graphics
GLUT (Continue)GLUT (Continue)More InteractionsMore Interactions
Yong CaoYong CaoVirginia TechVirginia Tech
References:References:Interactive Computer Graphics, Fourth Edition, Ed AngleInteractive Computer Graphics, Fourth Edition, Ed Angle
Orthographical Projection
Synthetic camera model
View angle and view volume
Clipping
Aspect ratio
Viewport mapping
Synthetic camera modelSynthetic camera model
View angle and view volumeView angle and view volume
ClippingClipping
Aspect ratioAspect ratio
Viewport mappingViewport mapping
Synthetic Camera Model
center of projection
image plane
projector
p
projection of p
View angle
View volume
Creating an orthographic view by moving the camera away from the projection plane.
Orthographical projection
Orthographic projectors with projection plane z = 0.
Orthographical projection
The default camera and an orthographic view volume.
Orthographical projection
Clipping
(a) Objects before clipping. (b) Image after clipping.
Aspect-ratio
(a) Viewing rectangle. (b) Display window.
A mapping to the viewport.
Reshaping the window
We can reshape and resize the OpenGL display window by pulling the corner of the window
What happens to the display?• Must redraw from application
• Two possibilities
– Display part of world
– Display whole world but force to fit in new window
Can alter aspect ratio
We can reshape and resize the OpenGL display We can reshape and resize the OpenGL display window by pulling the corner of the windowwindow by pulling the corner of the window
What happens to the display?What happens to the display?•• Must redraw from applicationMust redraw from application
•• Two possibilitiesTwo possibilities
–– Display part of worldDisplay part of world
–– Display whole world but force to fit in new windowDisplay whole world but force to fit in new window
Can alter aspect ratioCan alter aspect ratio
Reshape possibilities
original
reshaped
The Reshape callbackglutReshapeFunc(myreshape)
void myreshape( int w, int h)
• Returns width and height of new window (in pixels)• A redisplay is posted automatically at end of
execution of the callback • GLUT has a default reshape callback but you
probably want to define your own
The reshape callback is good place to put viewing functions because it is invoked when the window is first opened
glutReshapeFunc(myreshapeglutReshapeFunc(myreshape))
void void myreshapemyreshape( ( intint w, w, intint h)h)
•• Returns width and height of new window (in pixels)Returns width and height of new window (in pixels)•• A redisplay is posted automatically at end of A redisplay is posted automatically at end of
execution of the callbackexecution of the callback•• GLUT has a default reshape callback but you GLUT has a default reshape callback but you
probably want to define your ownprobably want to define your own
The reshape callback is good place to put The reshape callback is good place to put viewing functions because it is invoked viewing functions because it is invoked when the window is first openedwhen the window is first opened
Example Reshape (Demo)This reshape preserves shapes by making the viewport and world window have the same aspect ratio This reshape preserves shapes by making the viewport and This reshape preserves shapes by making the viewport and world window have the same aspect ratioworld window have the same aspect ratiovoid myReshape(int w, int h){
glViewport(0, 0, w, h);glMatrixMode(GL_PROJECTION); /* switch matrix mode */glLoadIdentity();if (w <= h)
gluOrtho2D(-2.0, 2.0, -2.0 * (GLfloat) h / (GLfloat) w,2.0 * (GLfloat) h / (GLfloat) w);
else gluOrtho2D(-2.0 * (GLfloat) w / (GLfloat) h, 2.0 * (GLfloat) w / (GLfloat) h, -2.0, 2.0);
glMatrixMode(GL_MODELVIEW); /* return to modelview mode */}
Toolkits and Widgets
Most window systems provide a toolkit or library of functions for building user interfaces that use special types of windows called widgets
Widget sets include tools such as• Menus
• Slidebars
• Dials
• Input boxes
But toolkits tend to be platform dependent
GLUT provides a few widgets including menus
Most window systems provide a toolkit or library of Most window systems provide a toolkit or library of functions for building user interfaces that use special types functions for building user interfaces that use special types of windows called of windows called widgetswidgets
Widget sets include tools such asWidget sets include tools such as
•• MenusMenus
•• SlidebarsSlidebars
•• DialsDials
•• Input boxesInput boxes
But toolkits tend to be platform dependentBut toolkits tend to be platform dependent
GLUT provides a few widgets including menusGLUT provides a few widgets including menus
Menus
GLUT supports pop-up menus• A menu can have submenus
Three steps• Define entries for the menu
• Define action for each menu item
– Action carried out if entry selected
• Attach menu to a mouse button
GLUT supports popGLUT supports pop--up menusup menus•• A menu can have submenusA menu can have submenus
Three stepsThree steps•• Define entries for the menuDefine entries for the menu
•• Define action for each menu itemDefine action for each menu item
–– Action carried out if entry selectedAction carried out if entry selected
•• Attach menu to a mouse buttonAttach menu to a mouse button
Defining a simple menu
In main.cIn In main.cmain.cmenu_id = glutCreateMenu(mymenu);glutAddmenuEntry(“clear Screen”, 1);
gluAddMenuEntry(“exit”, 2);
glutAttachMenu(GLUT_RIGHT_BUTTON);
entries that appear whenright button depressed
identifiers
clear screen
exit
Menu actions• Menu callback
• Note each menu has an id that is returned when it is created
• Add submenus by
glutAddSubMenu(char *submenu_name, submenu id)
•• Menu callbackMenu callback
•• Note each menu has an id that is returned when it is Note each menu has an id that is returned when it is createdcreated
•• Add submenus byAdd submenus by
glutAddSubMenu(charglutAddSubMenu(char *submenu_name, submenu id)*submenu_name, submenu id)
void mymenu(int id){
if(id == 1) glClear();if(id == 2) exit(0);
}
entry in parent menu
Other functions in GLUTDynamic Windows• Create and destroy during execution
Multiple Windows (Demo)
Changing callbacks during execution
Timersvoid glutTimerFunc( unsigned int msecs, void (*func)(int value), value);
Portable fonts• glutBitmapCharacter (See demo)
• glutStrokeCharacter (See demo)
Dynamic WindowsDynamic Windows
•• Create and destroy during executionCreate and destroy during execution
Multiple Windows Multiple Windows (Demo)(Demo)
Changing callbacks during executionChanging callbacks during execution
TimersTimersvoid void glutTimerFuncglutTimerFunc(( unsigned unsigned intint msecsmsecs, void (*, void (*func)(intfunc)(int value), value);value), value);
Portable fontsPortable fonts•• glutBitmapCharacterglutBitmapCharacter (See demo)(See demo)
•• glutStrokeCharacterglutStrokeCharacter (See demo)(See demo)
