Implementation: BaseCamera and Camera Data

Overview

A scene consists of  a set of  3D objects. Transformations such as translation, scaling and rotation brings them into life. The source for these transformations are mouse and keyboard inputs, which are further computed  resulting in camera placements, 

For example  the following diagram shows a multi color cube with  50 degrees pitch and 20 degrees yaw. The cube looks elongated horizontally because aspect ratio is not applied. 

Details

This post discusses camera  and camera data that are used in projections and animations.

The Camera data holds transformation information such as pitch, yaw and roll angles, translation, scaleby as well as Model, View and Projection matrix information of the 3D object. 

Coordinate System

OpenGL uses Right hand side coordinate system where +Z is pointing towards you.

Pitch, Yaw and Roll

A 3D object can rotate along all the three axes as shown below. 

Rotation along X Axis is called Pitch. Rotation along Y Axis is called Yaw. Rotation along Z Axis is called Roll

The following diagram shows how the positive rotation happens in Counter clockwise direction.

        Pitch(X Axis)                                    Yaw (Y Axis)                                  Roll (Z Axis)

Mouse and Keyboard input support

As discussed earlier, the BaseScene object captures all the Mouse and Keyboard activities such as key press, mouse button press, move etc. Later they are processed by BaseCamera class.
For example in BaseCamera class,  if a key is pressed, its scan code is stored. Similarly if mouse left button is pressed and the mouse is dragged, delta x and delta y are computed. 

The derived camera classes from BaseCamera use this information to further compute and  store additional information  in Camera Data structures.

For Example, ThreeDCamera class implements keyboard and mouse handling as below:

X key press  => Add pitch by 10 degrees.

Y key press  => Add yaw by  10 degrees.

Z key press  => Add roll by 10 degrees.

Mouse Drag using left button => Compute Pitch and Yaw angles from  Delta X, and Delta Y.

Later this is stored in ModelMatrixData class and shared with 3D objects in the scene to draw.

Camera and CameraData

There are many specialized camera classes that are associated with different types of camera data.

The class  diagram below shows their association, The light blue classes are camera data and the others are camera classes. 

The details will be provided in the next posts.

BaseCamera

BaseCamera implements handlers for mouse and keyboard events. This is a base class that can be further specialized. It's located in VedaOGLLib\Scene\BaseCamera.h. 

Constructor

Initializes hwnd with the Window handle of the hosting window.

Members

Name	Description
windowrect clientrect	Upon events like resize, windowrect and clientrect are updated. windowrect stores window rectangle of the hosting window after calling GetWindowRect() method. clientrect stores client rectangle of the hosting window after calling GetClientRect() method.
mouseX,mouseY deltaX,deltaY	Upon mouse move event, the current X and Y coordinates are stored in mouseX and mouseY. Delta of X and Y coordinates are stored in deltaX and deltaY.
mouseLeftDown mouseMiddleDown mouseRightDown	Upon mouse button down event, one of these  is set to true based on the button pressed. Rest are set to false.

Methods

Name	Description
CenterCursor	This method places the cursor at the center of the screen.
OnKey	This method handles keyboard input events.
OnMouseBtnDown	This method handle mouse button click events.
OnMouseMove	This method handle mouse move events.
OnMouseWheel	This method handles Mouse scroll wheel inputs.
UpdateWH	This method handles window resize events.

ModelMatrixData

As discussed earlier, ModelMatrixData class contains 3D information. It's updated by by ThreeDCamera class based on mouse and keyboard inputs and is shared with 3D objects based on BaseGeometry class  to redraw.

Members

Name	Description
pitch yaw roll	Computed values based on mouse and keyboard inputs. These are stored as degrees.
ScaleBy TranslateBy	Affine transformation values for scaling and Translation, These are stored 3x3 matrices.

Methods

Name	Description
augment	Augments itself from another ModelMatrixData object.
getModelMatrix	Returns self as 4x4 matrix.
Reset	Resets itself to scratch.