OpenGL L03-Utilities

1. Mohammad Shaker
mohammadshaker.com
@ZGTRShaker
2015
OpenGL Graphics
L03-Utilities

2. Viewports

3. Viewports
• glViewport(x, y, width, height)
• glViewport(0, 0, window_width, window_height);
– Will use all the window for drawing

4. Viewports
• Here is it, in ReSizeGLScene method.
GLvoid ReSizeGLScene(GLsizei width, GLsizei height)
{
if (height==0) { height=1; }
glViewport(0,0,width,height);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}

5. Depth Buffer

6. Depth Buffer
• Without and with Depth Test enabled:
glDisable(GL_DEPTH_TEST) glEnable(GL_DEPTH_TEST)

7. Depth Buffer Example
void DrawTriangle()
{
rtri+=0.2f;
glPushMatrix();
glLoadIdentity();
glTranslatef(-1.5f,0.0f,-6.0f);
glRotatef(rtri, 0, 1, 0);
glBegin(GL_TRIANGLES);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f( 0.0f, 1.0f, 0.0f);
glColor3f(0.0f,1.0f,0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glColor3f(0.0f,0.0f,1.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glEnd();
glPopMatrix();
}
void DrawQuad()
{
rquad-=0.15f;
glPushMatrix();
glLoadIdentity();
glTranslatef(1.5f,0.0f,-6.0f)
glRotatef(rquad, 1,0, 0);
glBegin(GL_QUADS);
glVertex3f(-1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glEnd();
glPopMatrix();
}
int DrawGLScene(GLvoid)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
DrawTriangle();
DrawQuad();
return TRUE;
}

8. Depth Buffer Example
void DrawTriangle()
{
rtri+=0.2f;
glPushMatrix();
glLoadIdentity();
glTranslatef(0f,0.0f,-6.0f);
glRotatef(rtri, 0, 1, 0);
glBegin(GL_TRIANGLES);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f( 0.0f, 1.0f, 0.0f);
glColor3f(0.0f,1.0f,0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glColor3f(0.0f,0.0f,1.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glEnd();
glPopMatrix();
}
void DrawQuad()
{
rquad-=0.15f;
glPushMatrix();
glLoadIdentity();
glTranslatef(0f,0.0f,-6.0f)
glRotatef(rquad, 1,0, 0);
glBegin(GL_QUADS);
glVertex3f(-1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glEnd();
glPopMatrix();
}
int DrawGLScene(GLvoid)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
DrawTriangle();
DrawQuad();
return TRUE;
}
Just changed these two lines

9. Depth Buffer Example
void DrawTriangle()
{
rtri+=0.2f;
glPushMatrix();
glLoadIdentity();
glTranslatef(0f,0.0f,-6.0f);
glRotatef(rtri, 0, 1, 0);
glBegin(GL_TRIANGLES);
glColor3f(1.0f,0.0f,0.0f);
glVertex3f( 0.0f, 1.0f, 0.0f);
glColor3f(0.0f,1.0f,0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glColor3f(0.0f,0.0f,1.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glEnd();
glPopMatrix();
}
void DrawQuad()
{
rquad-=0.15f;
glPushMatrix();
glLoadIdentity();
glTranslatef(0f,0.0f,-6.0f)
glRotatef(rquad, 1,0, 0);
glBegin(GL_QUADS);
glVertex3f(-1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f, 1.0f, 0.0f);
glVertex3f( 1.0f,-1.0f, 0.0f);
glVertex3f(-1.0f,-1.0f, 0.0f);
glEnd();
glPopMatrix();
}
int DrawGLScene(GLvoid)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity();
DrawTriangle();
DrawQuad();
return TRUE;
}

10. Depth Buffer Example
• Write the following in the DrawGLScene method:
– glDisable(GL_DEPTH_TEST);
• Now look at what happened. Without Depth Test, OpenGL will draw the objects
according to their ordering in the code.
With Depth Test Without Depth Test

11. Handling Input

12. Handling Input
if (keys[‘C'])
{
//Do Something
}
if(keys[VK_SHIFT])
{
//Do Something
}

13. Handling Input
if (keys[‘C'])
{
Crouch();
}
if(keys[VK_SHIFT])
{
speed += 0.1f;
}

14. Using 3D Models

17. Model and Mesh

18. Model and Mesh

19. Model and Bone

20. Using 3D Models
You can use any 3D Model Loader
http://nehe.gamedev.net/tutorial/model_loading/16004/

21. Using Model_3DS
• You can import and export .3ds files from 3d Design Programs:
– 3DS Max
– Maya
– Blender
– Google Sketch
– etc
• You can load and draw .3ds files by using Model_3DS class (or any other):
– Model_3DS.h
– Model_3DS.cpp
• You can garment (texture) 3ds models by using:
– 3Dtexture.h
– 3Dtexture.cpp

22. Using Model_3DS
• Add the following to the project directory:
– Model_3DS.h
– Model_3DS.cpp
– 3Dtexture.h
– 3Dtexture.cpp
• In Main.cpp / your class
– #include “Model_3DS.h”

23. Init Code
// Draw a triangle
// Draw a square
// a polygon
// another triangle
// ..etc
GLvoid DrawGLScene()
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt( 0.0, 0.0, 5.0,
0.0, 0.0, 0.0,
0.0, 1.0, 0.0 );
GLvoid init()
Global scope:

24. Using Models
GLvoid DrawGLScene()
//Set camera and projection
GLvoid init()
Global scope:

25. Using Models
model.Draw();
GLvoid DrawGLScene()
//Set camera and projection
model = Model_3DS();
model.Load(“ModelFilePath”);
GLvoid init()
#include “Model_3DS.h”
Model_3DS model;
Global scope:

26. Using Models
model.Draw();
model.pos.z += 0.1f;
GLvoid DrawGLScene()
//Set camera and projection
model = Model_3DS();
model.Load(“ModelFilePath”);
model.pos.x = 5;
model.scale= 2;
GLvoid init()
#include “Model_3DS.h”
Model_3DS model;
Global scope:

27. Using Models / Transforming Meshes
model.Draw();
model.Objects[2].rot.y += 2;
GLvoid DrawGLScene()
//Set camera and projection
model = Model_3DS();
model.Load(“ModelFilePath”);
model.pos.x = 5;
model.scale= 2;
GLvoid init()
#include “Model_3DS.h”
Model_3DS model;
Global scope:

28. Ok, but how about creating a 3D Model?
3D Max, Maya, google sketchup, … etc.

30. GLU Library Helper Functions

31. More Draw Functions
• Declare quadric variables first:
GLUquadric *quadric = gluNewQudric();
• Now draw what you want:
– Drawing Sphere:
void gluSphere(GLUquadric *qudric, Gldouble radius, GLint slices,
GLint stacks);
– Drawing Cylinder:
void gluCylinder(GLUquadric *qudric,GLdouble baseRadius, GLdouble topRadius,
Gldouble height, GLint slices, GLint stacks);
– Drawing Disk:
void gluDisk(GLUquadric *qudric, GLdouble innerRad, GLdouble outerRad,
GLint slices, GLint loops);

32. Draw Functions Parameters
• qobj
• The quadric object (created with gluNewQuadric).
• radius
• The radius of the sphere.
• slices
• The number of subdivisions around the z-axis (similar to lines of longitude).
• stacks
• The number of subdivisions along the z-axis (similar to lines of latitude).

33. Draw Functions Parameters

34. Fog

35. Why using Fog?

36. Why using Fog?
It’s cool!

37. Why using Fog?
And it can Hide a “Close” Far Clipping Plane

38. Fog
glFog(property, value)
• Depth Cueing
– Specify a range for a linear fog ramp
• GL_FOG_LINEAR
• Environmental effects
– Simulate more realistic fog
• GL_FOG_EXP
• GL_FOG_EXP2

39. Fog

40. Displaying Text

41. Displaying Text
• “glutFont.h”
• “glutFont.cpp”
• DrawGLScene()
glPushMatrix( );
glTranslatef(0,-1.2,0);
DisplayString(0,0,GLUT_BITMAP_HELVETICA_18,“Hello, How are you?");
glPopMatrix( );

42. Collision Detection

43. Collision Detection

44. Collision Detection
• Approximation

45. Collision Detection
• Approximation

46. Collision Detection
• Approximation

47. Collision Detection
• Approximation
When to use What?

48. Collision Detection
• Approximation
A better way to combine both approaches

49. Collision Detection
Hierarchical Modeling

50. Collision Detection

51. Collision Detection

52. Collision Detection

53. Collision Detection
In hierarchical model you would use both the large
sphere, and the small spheres.

54. Collision Detection
Quad Tree Approach

55. Picking Objects in 3D Scene

56. Picking with Ghoscher
http://ghoscher.me/2010/11/25/xna-picking-tutorial-part-i

57. Picking with Ghoscher
http://ghoscher.me/2010/11/25/xna-picking-tutorial-part-i

58. Picking
• The picking region is usually specified in a piece of code like this:
glMatrixMode (GL_PROJECTION);
glLoadIdentity();
gluPickMatrix(x, y, width, height, viewport);
• The picking matrix is the rare situation where the standard projection matrix
(perspective or ortho) is multiplied onto a non-identity matrix.
• Each hit record contains:
• number of names per hit
• smallest and largest depth values
• all the names

59. Picking
• Programming steps
– Restrict “drawing” to small region near pointer
Use glupickmatrix() on projection matrix
– Enter selection mode; re-render scene
– Primitives drawn near cursor cause hits
– Exit selection; analyze hit records

60. Picking with Ray Casting
http://antongerdelan.net/opengl/raycasting.html

61. Now why spheres?

62. Now why spheres?
Hitting the body’s bounding
sphere is easier and faster!

63. Lens Flare
http://nehe.gamedev.net/tutorial/3d_lens_flare_with_occlusion_testing/16007/

64. Lens Flare
Howto?

65. Lens Flare
Using ProjectionMatrix

66. Lens Flare – Using Projection Matrix

67. Particle Systems
Dust, flares, fire, etc.