libGLI - New Object HowTo

by Benjamin Schieder

v0.1, 03. Jan 2003

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This HowTo mainly shows how to create a new 3D-Object using and for use with libGLI
Copyright (c) 2003 Benjamin Schieder

1. Introduction

• 1.1 Author
• 1.2 Getting

2. Problem

• 2.1 Requirements
• 2.2 Problem-Description

3. Solution

• 3.1 Start
• 3.2 Adding the class
• 3.3 Adding the Draw() code
• 3.4 Effects
• 3.5 Multiple Objects

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1. Introduction

1.1 Author

The Author of this document is also the current Maintainer of libGLI which, at the time of writing, can be found at http://www.crash-override.net.
You contact him via E-Mail via 'libgli at scavenger dot homeip dot net'

1.2 Getting

This document is maintained together with the libGLI library at its website http://www.crash-override.net.

1.3 License

Copyright (c) 2003 Benjamin Schieder

2. Problem

2.1 Requirements

To create a new object to use it with libGLI you need the following:

1. libGLI - http://www.crash-override.net./libgli/main.php
2. An implementation of OpenGL - Mesalib, NVidia's GLX driver or whatever suits your needs (ask your distributor)
3. A C++-Compiler and standard header files (*.h)
4. Knowledge about OpenGL-Programming
5. The will to do it

2.2 Problem-Description

So, now you've successfully downloaded, compiled and installed libGLI, you understand how the demo-programs work and adapted them a little so that you now have a basic understanding of how libGLI works. Now you want to create your own object for your own program, say, a game.
This HowTo will tell you how to create a simple 3D-Object with libGLI.

3. Solution

3.1 Start

We start out with a simple program opening our OpenGL-Window with a width of 800600 using the GLUT library.

#include <stdio.h> #include <stdlib.h> #include <math.h> #include <time.h> #include <GL/glut.h> #include "gli.h" int WindW, WindH; CGLI_Interface iface; void Reshape(int width, int height){ glViewport(0, 0, width, height); glMatrixMode(GL_PROJECTION); glLoadIdentity(); if (width <= height){ glOrtho(-100.0, 100.0, -100.0*(GLfloat)height/(GLfloat)width, 100.0*(GLfloat)height/(GLfloat)width, -100.0, 100.0); } else { glOrtho(-100.0*(GLfloat)width/(GLfloat)height, 100.0*(GLfloat)width/(GLfloat)height, -100.0, 100.0, -100.0, 100.0); } glMatrixMode(GL_MODELVIEW); WindW = width; WindH = height; } void Draw(void){ glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); iface.Draw(); glFlush(); glutSwapBuffers(); } void mouse(int button, int state, int x, int y){ switch (button){ case GLUT_LEFT_BUTTON: button = GLI_MOUSE_BUTTON_LEFT; break; case GLUT_MIDDLE_BUTTON: button = GLI_MOUSE_BUTTON_MIDDLE; break; case GLUT_RIGHT_BUTTON: button = GLI_MOUSE_BUTTON_RIGHT; break; } switch (state){ case GLUT_DOWN: state = GLI_MOUSE_BUTTON_DOWN; break; case GLUT_UP: state = GLI_MOUSE_BUTTON_UP; break; } iface.SendMouseParameters(GLI_MOUSE_CLICK, button, state, x, WindH-y); } void mouse2(int x, int y){ iface.SendMouseParameters(GLI_MOUSE_MOTION_BUTTON, GLI_MOUSE_BUTTON_NONE, GLI_MOUSE_BUTTON_NONE, x, WindH-y); } void mouse3(int x, int y){ iface.SendMouseParameters(GLI_MOUSE_MOTION, GLI_MOUSE_BUTTON_NONE, GLI_MOUSE_BUTTON_NONE, x, WindH-y); } static void Key(unsigned char key, int x, int y){ switch (key){ case 27: exit(0); break; } } void timf(int value){ glutPostRedisplay(); glutTimerFunc(30, timf, 0); } void CallBack(GLuint id){ exit(0); } int main(int argc, char *argv[]){ WindW = 800; WindH = 600; glutInit(&argc, argv); glutInitWindowSize(WindW, WindH); glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH); (void)glutCreateWindow("Image Demo"); glutReshapeFunc(Reshape); glutDisplayFunc(Draw); glutMouseFunc(mouse); glutMotionFunc(mouse2); glutPassiveMotionFunc(mouse3); glutKeyboardFunc(Key); glutTimerFunc(10, timf, 0); glClearColor(0, 0, 0, 0); glColor3f(1, 1, 1); glEnable(GL_DEPTH_TEST); glEnable(GL_TEXTURE_2D); glutMainLoop(); return 0; }

3.2 Adding the class

For the sake of simplicuty we just add the new class to the existing code instead of a separate file.
DO NOT DO THAT IN PRODUCTION CODE!!!

#include <stdio.h> #include <stdlib.h> #include <math.h> #include <time.h> #include <GL/glut.h> #include "gli.h" int WindW, WindH; CGLI_Interface iface; class CGLI_Pyramid : public CGLI_Object { public: CGLI_Pyramid(); virtual ~CGLI_Pyramid(); virtual void Draw(); // Draw method virtual void UpdateObject(); virtual void DoAnimationTick(); protected: virtual void ProcessInternalCallBack(GLuint obj_id); }; CGLI_Pyramid::CGLI_Pyramid(){ } CGLI_Pyramid::~CGLI_Pyramid(){ } void CGLI_Pyramid::Draw(){ } void CGLI_Pyramid::UpdateObject(){ } void CGLI_Pyramid::DoAnimationTick(){ } void CGLI_Pyramid::ProcessInternalCallBack(GLuint obj_id){ } CGLI_Pyramid pyramid;

Here we inserted a class CGLI_Pyramid and created the instance "pyramid". Note that all methods from CGLI_Object are inherited which include, but are not limited to, Show, Hide, SetRotation, SetPosition and others.

3.3 Adding the Draw() code

Now, what good does this do when the object does not draw anything to the screen? Here we add the Draw() code:

CGLI_Pyramid::CGLI_Pyramid(){ } CGLI_Pyramid::~CGLI_Pyramid(){ } void CGLI_Pyramid::Draw(){ glBegin(GL_TRIANGLES); glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Front) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f(-1.0f,-1.0f, 1.0f); // Left Of Triangle (Front) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f( 1.0f,-1.0f, 1.0f); // Right Of Triangle (Front) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Right) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f( 1.0f,-1.0f, 1.0f); // Left Of Triangle (Right) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f( 1.0f,-1.0f, -1.0f); // Right Of Triangle (Right) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Back) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f( 1.0f,-1.0f, -1.0f); // Left Of Triangle (Back) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f(-1.0f,-1.0f, -1.0f); // Right Of Triangle (Back) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Left) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f(-1.0f,-1.0f,-1.0f); // Left Of Triangle (Left) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f(-1.0f,-1.0f, 1.0f); // Right Of Triangle (Left) glEnd(); }

This will draw a 3-D Pyramid made of three colors to the screen.


int main(int argc, char *argv[]){ WindW = 800; WindH = 600; glutInit(&argc, argv); glutInitWindowSize(WindW, WindH); glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH); (void)glutCreateWindow("Image Demo"); glutReshapeFunc(Reshape); glutDisplayFunc(Draw); glutMouseFunc(mouse); glutMotionFunc(mouse2); glutPassiveMotionFunc(mouse3); glutKeyboardFunc(Key); glutTimerFunc(10, timf, 0); glClearColor(0, 0, 0, 0); glColor3f(1, 1, 1); pyramid.SetScalingFactor(25); pyramid.SetRotation(45, 45, 0); iface.AddObject(&pyramid); glEnable(GL_DEPTH_TEST); glEnable(GL_TEXTURE_2D); glutMainLoop(); return 0; }

Also note the 3 new lines in the main() part. This adds the Object to the screen using the CGLI_Interface 'iface'.

3.4 Effects

Now, an object that just sits there is pretty boring. Now we let the pyramid do something when clicked on with the mouse. To achive this, we insert two new variables and some code into the constructor, the Draw(), and the ProcessInternalCallBack():

class CGLI_Pyramid : public CGLI_Object { public: CGLI_Pyramid(); virtual ~CGLI_Pyramid(); virtual void Draw(); // Draw method virtual void UpdateObject(); virtual void DoAnimationTick(); protected: virtual void ProcessInternalCallBack(GLuint obj_id); GLint m_rot_add; GLint m_click_event_type; }; CGLI_Pyramid::CGLI_Pyramid(){ m_rot_add = 0; m_click_event_type = 0; }

Two new variables to play with. m_rot_add will hold the value of additional rotation. It's additional becaule CGLI_Object::SetRotation will already hold some information of this kind.
m_click_event_type will indicate which rotation will be done:
0: Z-Axis
1: Y-Axis
2: X-Axis


CGLI_Pyramid::~CGLI_Pyramid(){ } void CGLI_Pyramid::Draw(){ if (m_rot_add > 0){ switch (m_click_event_type) { case 0: glRotatef(m_rot_add, 0, 0, 1); break; case 1: glRotatef(m_rot_add, 0, 1, 0); break; case 2: glRotatef(m_rot_add, 1, 0, 0); break; } }

Here the Rotation will be added before be actually draw something.


glBegin(GL_TRIANGLES); glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Front) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f(-1.0f,-1.0f, 1.0f); // Left Of Triangle (Front) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f( 1.0f,-1.0f, 1.0f); // Right Of Triangle (Front) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Right) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f( 1.0f,-1.0f, 1.0f); // Left Of Triangle (Right) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f( 1.0f,-1.0f, -1.0f); // Right Of Triangle (Right) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Back) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f( 1.0f,-1.0f, -1.0f); // Left Of Triangle (Back) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f(-1.0f,-1.0f, -1.0f); // Right Of Triangle (Back) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Left) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f(-1.0f,-1.0f,-1.0f); // Left Of Triangle (Left) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f(-1.0f,-1.0f, 1.0f); // Right Of Triangle (Left) glEnd(); if (m_rot_add > 0){ switch (m_click_event_type) { case 0: glRotatef(-m_rot_add, 0, 0, 1); break; case 1: glRotatef(-m_rot_add, 0, 1, 0); break; case 2: glRotatef(-m_rot_add, 1, 0, 0); break; } m_rot_add--; }

Of course, we must not forget to undo the rotation from before.
m_rot_add will also be decreasd by 1.


} void CGLI_Pyramid::UpdateObject(){ } void CGLI_Pyramid::DoAnimationTick(){ } void CGLI_Pyramid::ProcessInternalCallBack(GLuint obj_id){ if (m_rot_add != 0){ return; } if (m_event_type == GLI_CLICKED){ m_rot_add = 360; m_click_event_type++; if (m_click_event_type == 3){ m_click_event_type = 0; } } }

In this method we check if an event took place. But only, if the previous Event is already handled (m_rot_add == 0).
If so, we set m_rot_add to 360 (Degrees) and increase m_click_event_type by 1 and wrap it to 0 if it is equal to 3.

Note that there are no changes in the main() part.

3.5 Multiple Objects

As a last thing we add a second pyramid just for fun :)

#include <stdio.h> #include <stdlib.h> #include <math.h> #include <time.h> #include <GL/glut.h> #include "gli.h" int WindW, WindH; CGLI_Interface iface; class CGLI_Pyramid : public CGLI_Object { public: CGLI_Pyramid(); virtual ~CGLI_Pyramid(); virtual void Draw(); // Draw method virtual void UpdateObject(); virtual void DoAnimationTick(); protected: virtual void ProcessInternalCallBack(GLuint obj_id); GLint m_rot_add; GLint m_click_event_type; }; CGLI_Pyramid::CGLI_Pyramid(){ m_rot_add = 0; m_click_event_type = 0; } CGLI_Pyramid::~CGLI_Pyramid(){ } void CGLI_Pyramid::Draw(){ if (m_rot_add > 0){ switch (m_click_event_type) { case 0: glRotatef(m_rot_add, 0, 0, 1); break; case 1: glRotatef(m_rot_add, 0, 1, 0); break; case 2: glRotatef(m_rot_add, 1, 0, 0); break; } } glBegin(GL_TRIANGLES); glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Front) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f(-1.0f,-1.0f, 1.0f); // Left Of Triangle (Front) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f( 1.0f,-1.0f, 1.0f); // Right Of Triangle (Front) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Right) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f( 1.0f,-1.0f, 1.0f); // Left Of Triangle (Right) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f( 1.0f,-1.0f, -1.0f); // Right Of Triangle (Right) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Back) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f( 1.0f,-1.0f, -1.0f); // Left Of Triangle (Back) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f(-1.0f,-1.0f, -1.0f); // Right Of Triangle (Back) glColor3f(1.0f,0.0f,0.0f); // Red glVertex3f( 0.0f, 1.0f, 0.0f); // Top Of Triangle (Left) glColor3f(0.0f,0.0f,1.0f); // Blue glVertex3f(-1.0f,-1.0f,-1.0f); // Left Of Triangle (Left) glColor3f(0.0f,1.0f,0.0f); // Green glVertex3f(-1.0f,-1.0f, 1.0f); // Right Of Triangle (Left) glEnd(); if (m_rot_add > 0){ switch (m_click_event_type) { case 0: glRotatef(-m_rot_add, 0, 0, 1); break; case 1: glRotatef(-m_rot_add, 0, 1, 0); break; case 2: glRotatef(-m_rot_add, 1, 0, 0); break; } m_rot_add--; } } void CGLI_Pyramid::UpdateObject(){ } void CGLI_Pyramid::DoAnimationTick(){ } void CGLI_Pyramid::ProcessInternalCallBack(GLuint obj_id){ if (m_rot_add != 0){ return; } if (m_event_type == GLI_CLICKED){ m_rot_add = 360; m_click_event_type++; if (m_click_event_type == 3){ m_click_event_type = 0; } } } CGLI_Pyramid pyramid; CGLI_Pyramid pyramid2; void Reshape(int width, int height){ glViewport(0, 0, width, height); glMatrixMode(GL_PROJECTION); glLoadIdentity(); if (width <= height){ glOrtho(-100.0, 100.0, -100.0*(GLfloat)height/(GLfloat)width, 100.0*(GLfloat)height/(GLfloat)width, -100.0, 100.0); } else { glOrtho(-100.0*(GLfloat)width/(GLfloat)height, 100.0*(GLfloat)width/(GLfloat)height, -100.0, 100.0, -100.0, 100.0); } glMatrixMode(GL_MODELVIEW); WindW = width; WindH = height; } void Draw(void){ glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); glLoadIdentity(); iface.Draw(); glFlush(); glutSwapBuffers(); } void mouse(int button, int state, int x, int y){ switch (button){ case GLUT_LEFT_BUTTON: button = GLI_MOUSE_BUTTON_LEFT; break; case GLUT_MIDDLE_BUTTON: button = GLI_MOUSE_BUTTON_MIDDLE; break; case GLUT_RIGHT_BUTTON: button = GLI_MOUSE_BUTTON_RIGHT; break; } switch (state){ case GLUT_DOWN: state = GLI_MOUSE_BUTTON_DOWN; break; case GLUT_UP: state = GLI_MOUSE_BUTTON_UP; break; } iface.SendMouseParameters(GLI_MOUSE_CLICK, button, state, x, WindH-y); } void mouse2(int x, int y){ iface.SendMouseParameters(GLI_MOUSE_MOTION_BUTTON, GLI_MOUSE_BUTTON_NONE, GLI_MOUSE_BUTTON_NONE, x, WindH-y); } void mouse3(int x, int y){ iface.SendMouseParameters(GLI_MOUSE_MOTION, GLI_MOUSE_BUTTON_NONE, GLI_MOUSE_BUTTON_NONE, x, WindH-y); } static void Key(unsigned char key, int x, int y){ switch (key){ case 27: exit(0); break; } } void timf(int value){ glutPostRedisplay(); glutTimerFunc(30, timf, 0); } void CallBack(GLuint id){ exit(0); } int main(int argc, char *argv[]){ WindW = 800; WindH = 600; glutInit(&argc, argv); glutInitWindowSize(WindW, WindH); glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH); (void)glutCreateWindow("Image Demo"); glutReshapeFunc(Reshape); glutDisplayFunc(Draw); glutMouseFunc(mouse); glutMotionFunc(mouse2); glutPassiveMotionFunc(mouse3); glutKeyboardFunc(Key); glutTimerFunc(10, timf, 0); glClearColor(0, 0, 0, 0); glColor3f(1, 1, 1); pyramid.SetScalingFactor(25); pyramid.SetPosition(-45, 0, 0); pyramid.SetRotation(45, 45, 0); iface.AddObject(&pyramid); pyramid2.SetScalingFactor(25); pyramid2.SetPosition(45, 0, 0); pyramid2.SetRotation(45, 45, 0); iface.AddObject(&pyramid2); glEnable(GL_DEPTH_TEST); glEnable(GL_TEXTURE_2D); glutMainLoop(); return 0; } © 2005 - 2117 http://www.crash-override.net/ Design © PsyBorg