ofBackground( ofColor::white );

This sets the background to the white color.

float w = ofGetWidth();

The ofGetWidth() function returns the current width of the application's screen in pixels. In this code, this value is set to the variable w.

float h = ofGetHeight();

The ofGetHeight() function returns the current height of the application's screen in pixels. In this code, this value is set to the variable h.

ofLine( 100, 200, 300, 400 );

This draws a line segment connecting the points (100, 200) and (300, 400).

ofRect( 100, 200, 300, 400 );

This draws a rectangle with the top-left corner (100, 200), a width of 300 pixels, and a height of 400 pixels.

The ofSetRectMode( OF_RECTMODE_CENTER ) command enables the mode for specifying the center of the rectangle instead of the top-left corner. The ofSetRectMode( OF_RECTMODE_CORNER ) command enables the top-left corner mode back.

ofTriangle( 10, 20, 30, 40, 50, 60 );

This draws a triangle with the vertices (10, 20), (30, 40), and (50, 60).

ofCircle( 100, 200, 30 );

This draws a circle with the center (100, 200) and a radius of 30.

The ofSetCircleResolution( 10 ) command sets the circle resolution to 10, that is, the circle will be drawn consisting of 10 line segments.

ofFill();

This enables the mode for drawing filled figures.

ofNoFill();

This enables the mode for drawing unfilled figures.

ofSetColor( 100, 150, 200 );

This sets the drawing color with a red value of 100, a green value of 150, and a blue value of 200.

ofSetColor(255,200);

This sets the drawing color with the red, green, and blue values equal to 255 and the alpha value equal to 200.

To enable additive blending, use the ofEnableBlendMode( OF_BLENDMODE_ADD ) command.

To enable alpha blending back, use the ofEnableAlphaBlending() command. (See Chapter 4, Working with Raster Graphics – Images, Videos, and Shaders, for details.)

ofSetColor( ofColor::yellow );

This sets the yellow drawing color.

ofPushMatrix();

This stores the current coordinate system to a special stack.

ofPopMatrix();

This restores the coordinate system from the stack.

ofTranslate( 100, 200 );

This translates the coordinate system by (200, 100) pixels.

ofRotate( 90 );

This rotates the coordinate system by 90 degrees clockwise.

ofScale( 2, 2 );

This scales the coordinate system; all objects will grow bigger by two times.