10. Open GL & Glut Mouse & Camera - 3D Graphics and Game Development Course

OpenGL & GLUTMouse Interaction &

Camera ControlMouse events, Advanced camera control

George Georgiev

http://academy.telerik.com

Technical Trainer

academy.telerik.com

/.../3d-game-developme

nt-opengl

George AtanasovFront-End Developer

http://academy.telerik.com/

http://academy.telerik.com/school-academy/meetings/details/2011/09/27/3d-game-development-opengl



Table of Contents

GLUT Mouse Interaction Mouse up/down events

Passive motion

Active motion

OpenGL Camera Default transformation

“Manual” control

Custom camera class

2

GLUT Mouse Interaction

Mouse event callbacks


4

GLUT provides mouse detection capabilities Advantages

Multi-platform

Similar to other GLUT routines

Easy to code

Disadvantages Doesn’t receive device information

No scroll information

Unstable ‘leave’ and ‘enter’ events


5

Detecting mouse buttons Registering callback function

glutMouseFunc(void(*func)(int button, int state, int x, int y))

func – mouse button callback function

button – mouse button raising the event

state – type of event

x, y – cursor coordinates (from upper left corner)


6

Detecting mouse buttons (2) Callback parameter values

button

GLUT_LEFT_BUTTON

GLUT_MIDDLE_BUTTON

GLUT_RIGHT_BUTTON

state

GLUT_DOWN

GLUT_UP


7

Detecting mouse buttons (2) Callback parameter values

button

GLUT_LEFT_BUTTON

GLUT_MIDDLE_BUTTON

GLUT_RIGHT_BUTTON

state

GLUT_DOWN

GLUT_UP


8

Detecting movement Types

Passive

Mouse moves

No buttons pressed

Active

Mouse moves

One or more buttons pressed


9

Passive motion Registering callback function

glutPassiveMotionFunc(void(*func)(int x, int y))

func – mouse passive motion callback



10

Active motion Registering callback function

glutMotionFunc(void(*func)(int x, int y))

func – mouse active motion callback


GLUT Mouse Interaction GLUT Mouse leave and entry routines Detect when cursor leaves and

enters window

Registering callback glutEntryFunc(void(*func)(int state))

Func – callback handling cursor leaving and entering window

State – enter or leave event

GLUT_ENTERED

GLUT_LEFT11

GLUT Mouse Interaction Cursor-related routines

glutWarpPointer (int x, int y) Sends cursor to specified coordinates

glutSetCursor (int cursor) Sets the cursor image (style) for the

window

Values: GLUT_CURSOR_NONE, GLUT_CURSOR_INFO,

GLUT_CURSOR_DESTROY, etc…

Google for more (much, much more)

12

Mouse Interaction Object-oriented mouse handling

Custom mouse class Current cursor position

Last cursor position and/or drag-begin position

Current mouse button states

Last mouse button states

Cursor style

Anything else you can think of

13

Custom mouse classLive Demo

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Mouse Interaction




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OpenGL Camera ControlBasic and Advanced camera positioning

OpenGL Camera Control Default camera position

Set up with glLoadIdentity()

Centered at coordinate system center (0, 0, 0)

Rotation around all axes – zero (0, 0, 0)

Looks down the negative Z axis

17

OpenGL Camera Control “Manual” control

Applying transformations to the world Opposite those of the camera

Applied before rendering anything else

Why not use gluLookAt ? Does the same things without asking

you

Gives you less freedom

Future – transformations won’t be deprecated

gluLookAt most probably will

18

OpenGL Camera Control “Manual” control (2)

Imagining it – three options Positioning the ‘world’

Opposite to the location and orientation of the ‘camera’

Positioning the ‘camera’ away from the ‘world’

Positioning the coordinate system of the ‘paintbrush’

Either way, the result is the same19

OpenGL Camera Control “Manual” control (3)

The steps Load default view

glLoadIdentity – not really camera-related

Move away

glTranslate*

Look away

glRotate*

Move on to lighting, drawing objects, etc…

20

OpenGL Camera control Moving away

glTranslate* Specifies a translation

Applies to any subsequently drawn geometry

You could imagine it moves the ‘paintbrush’

Used for all object positioning (not just camera)

Say we want the camera at C(0, 0, 20) glTranslatef(0, 0, -20)

21

OpenGL Camera control Looking away

glRotate* Specifies a rotation

Applies to any subsequently drawn geometry

You could imagine it turns the ‘paintbrush’

Used for all object positioning (not just camera)

If we want the camera to look right 90 degrees glRotatef (-90, 0, 1.0, 0)

22

OpenGL Camera control Looking away (2) – explanation

glRotatef parameters 1st parameter – degrees to rotate

2nd, 3rd, 4th parameter – multiplier for resultant rotation on x, y, z axis respectively

Example: glRotatef (90, 0.5, 1.0, 0.0) = rotate by

45 degrees round X

90 degrees round Y

0 degrees round Z 23


glRotatef positive rotations Positive rotation round Y

24


glRotatef positive rotations Positive rotation round X

25


glRotatef positive rotations Positive rotation round Z

26

OpenGL Camera Control Basic camera control

So far we can Set the location of the camera

Set the orientation of the camera

Limit the rotation of the camera

Hard to do that with gluLookAt

27

OpenGL Camera Control Advanced camera control

A good camera can Move forward and backward

Strafe left and right

Move up and down

Look left and right

Look up and down

Tilt left and right

“LookAt”28

OpenGL Camera Control Custom camera class

Fields Location, last location

Rotation (Euler angles), last rotation

Forward vector

Right vector

Upward vector

Speed? Maximum upward (x) rotation? Etc…

29

OpenGL Camera Control Custom camera class

Methods Set/Get location

Set/Get rotation

Move forward, backward, upward, downward

Strafe left, right

Look up, down, left, right

Tilt left, tilt right

“Look at”, “sweep left/right”, “fly to” ? Etc…

30

Custom camera classLive Demo

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Mouse Interaction & Camera control










































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10. Open GL & Glut Mouse & Camera - 3D Graphics and Game Development Course