05

Bootcamp 05

15 minutes, split into groups and share homework

3D, pixels, recursion

15 minutes of share work time, 3-4 person groups.

going inside of an image. pixels

load an image and read its pixels with getColor, learn about the ofColor object and getBrightness, and our first loop inside a loop. discuss the row/column order of execution.

void ofApp::draw(){
  ofBackground(0);
  img.draw(0,0);
  for (int i = 0; i < img.getWidth(); i+=10){
    for (int j = 0; j < img.getHeight(); j+=10){
      float brightness = img.getColor(i,j).getBrightness();
      ofDrawCircle(img.getWidth()+i, j, ofMap(brightness, 0, 255, 0, 5));
    }
  }
}

For video, ofVideoGrabber, you will want to use getPixels() and iterate over the array. review sizes of data types (chart below). unsigned means everything is in the positive range. unsigned char is 0-255, like our colors.

image array span goes [0]:red, [1]:green, [2]:blue, (and 4 if alpha) neighboring pixels are 3 indices away.

1 bytes _  8 bits _ char   _ -128 to 127
2 bytes _ 16 bits _ short  _ -32,768 to 32,768
4 bytes _ 32 bits _ int    _ -1 billion to 1 billion
8 bytes _ 64 bits _ long   _ very very very big range
4 bytes _ 32 bits _ float  _ (about 7 decimals)
8 bytes _ 64 bits _ double _ (about 14 decimals)

Recursion

talk about how recursion is similar to and unlike a loop. we need to repeat for a while but eventually stop.

void ofApp::splitRectangle(float x, float y, float width, float height){
  if (width > 1 && ofRandom(0, 1) > 0.5){
    splitRectangle(x          , y           , width/2, height/2);
    splitRectangle(x + width/2, y           , width/2, height/2);
    splitRectangle(x + width/2, y + height/2, width/2, height/2);
    splitRectangle(x          , y + height/2, width/2, height/2);
  } else {
    ofDrawRectangle(x,y,width, height);
  }
  //ofDrawRectangle(x,y,width, height);
}

3D

Students should know about transforms and push and pop matrix before this. Use ofEasyCam. An ofCamera is like a push/pop matrix, it wraps code, and additionally transforms the space.

Rotate the grass-colored plane to lie flat. discuss the three axes parameters of ofRotateDeg. Use ofEnableDepthTest() to disable painter's algorithm. Talk about z-fighting, ofLight, and how cameras have setPosition and lookAt.

void ofApp::draw(){
  cam.begin();
  ofSetColor(100, 20, 10);  // brown
  ofDrawBox(0, 50, 0, 100, 100, 100);
  
  ofPushMatrix();
    ofSetColor(50, 190, 10);  // green
    ofRotateDeg(90, 1, 0, 0);
    // ground plane
    ofDrawRectangle(-250, -250, 500, 500);
  ofPopMatrix();
  cam.end();
}

Wrap up

• How to share openFrameworks apps, debug release, OS specific builds.
• ofxAddons
• continue sharing screenshots on Slack