Submodule 16.3: Colors

Color functions

In order to apply color to p5.js elements we use the fill () function.

We can write colors in any of RGB, RGBA, Hex and supported named color strings.

• See More info about supported colors in p5.js

In order to define the color of the border of p5.js elements we use the stroke() function. 

We can increase or decrease the border weight by using the strokeWeight() function. 

If we don't want our elements to be filled, we use the noFill()function, whereas if we don't want them to have border we use the noStroke()

Example 

Here is an example where all of the above functions are used:

function setup() {
  // create canvas
  createCanvas(800,500);
  }
function draw () {
  // set background color
  background('#B1CBBB');
  //use the fill function to color the triangle
  fill('#EEA29A');
  // use the noStroke function to remove border
  noStroke();
  triangle(width/2,height/2,500,400,300,400);
  // use the noFill function to remove the fill of our element
  noFill();
  // use the stroke to change the color of the border
  stroke('#D64161');
  // use the strokeWeight to change the border weight
  strokeWeight(5);
  triangle(width/2,height/2,500,100,300,100);
}

Result of the above code:

• See more about the fill() function
• See more about the noFill() function
• See more about the stroke() function
• See more about the noStroke() function
• See more about the strokeWeight() function

Color rules

In order to define the color of different p5.js elements it is important to understand the color rules.

When we want to color an element, we have to apply the appropriate functions prior to drawing the element.

Example:

function setup() {
  // create canvas
  createCanvas(800,500);
  // set background color
  background('orange');
}
function draw () {
  fill('red');
  stroke('#f12e78');
  ellipse(width/2,height/2, 50);
  fill('#DC143C');
  stroke('#FFA500');
  ellipse(500,height/2, 50);
}

Result of the above code:

If we don't define any different color all the elements that will be drawn after this, they will have the same colors.

Example:

function setup() {
  // create canvas
  createCanvas(800,500);
  // set background color
  background('orange');
}
function draw () {
  fill('red');
  stroke('#f12e78');
  ellipse(width/2,height/2, 50);
  ellipse(width/2,height/3, 50);
  rect(width/2,height/6, 50,50);
  ellipse(width/4,height/2, 50);
}

Result of the above code:

If we want each color function to be applied only on specific elements, we can position our elements in between the push() and pop() functions.

For example the above can be modified as :

function setup() {
  // create canvas
  createCanvas(800,500);
  // set background color
  background('orange');
}
function draw () {
  push();
  fill('red');
  stroke('#f12e78');
  ellipse(width/2,height/2, 50);
  pop();
  ellipse(width/2,height/3, 50);
  rect(width/2,height/6, 50,50);
  ellipse(width/4,height/2, 50);
}

Result of the above code:

Exercise

1. Open your Visual Studio editor and the p5yourName folder.
2. Open the file ex812.js in your editor and save it as ex832.js
3. Open the file ex812.html in your editor and save it as ex832.html
4. In the ex832.html file, update the link to ex832.js  from exersice812.js
5. Go to the index.html file and create, under Module 8, a link to the ex832.html  file with the title "Color rules".

Modify the ex832.jsfile to apply colors to the face. You can see here an example.

Answer:

function setup() {
  createCanvas(800, 600);
  // set background color
  background('#D66761');
}
function draw() {
  // state the fill color of the shape
  fill('#FBEFCC');
  // state the border color of the shape
  stroke('#FBEFCC');
  // state the border weight of the shape
  strokeWeight(2);
  // create the face ellipse
  ellipse(width/2,height/2,200,300)
  // state the border color of the outer eye circle
  stroke('#A2836E');
  // for the left eye
  // draw the base ellipse, the sclera/“white of the eye”
  ellipse(350,275,50,25);
  // state the border of the iris
  stroke('black');
  // draw the Iris for the eye
  ellipse(350,275,25);
  // fill the center of the eye
  fill('#034F84');
  // color the border
  stroke('#034F84');
  // draw the center of the eye
  ellipse(350,275,12.5);
  // state the border color of the outer eye circle
  stroke('#A2836E');
  // for the right eye
  // draw the base ellipse for the eye, the sclera/“white of the eye”
  noFill();
  ellipse(450,275,50,25);
  // state the border of the iris
  stroke('black');
  // draw the Iris for the eye
  ellipse(450,275,25);
  // fill the center of the eye
  fill('#034F84');
  // color the border
  stroke('#034F84');
  // draw the center of the eye
  ellipse(450,275,12.5);
}

Do a Git commit with the message "Color rules".

• See more about the push() function
• See more about the pop() function

Alpha value - Transparency

When we want to determine the alpha value of a p5.js element, we define a fourth value for the color.

The smaller the alpha value the more transparent the element. 

Example 

Here is an example code of two ellipses with different alpha values :

function setup() {
  // create canvas
  createCanvas(800,500);
  // set background color
  background('#B2B2B2');
}
function draw () {
  //this ellipse will have a low transparency value
  fill (175,68,39,50);
  ellipse(width/2,height/2,100);
  // this ellipse will have a high transparency value
  fill (124,156,39,5);
  ellipse(450,height/2,100);
}

Result of the above code:

Exercise

1. Open your Visual Studio editor and the p5yourName folder.
2. Open the file ex812.js in your editor and save it as ex833.js
3. Open the file ex812.html in your editor and save it as ex833.html
4. In the ex833.html file, update the link to ex833.js  from exersice812.js
5. Go to the index.html file and create, under Module 8, a link to the ex833.html  file with the title "Alpha value".

Modify the ex833.jsfile to create an ellipse which will move horizontally from the left to the right end of the canvas and will change its color and alpha value according to the direction it has. You can see here an example.

Answer:

// create a variable tp control the direction of the ellipse
let control = false;
// make ellipse starting from the left end of the canvas
let i=30;
function setup() {
  // create canvas
  createCanvas(800,500);
  // set background color
  background('#31bc33');
}
function draw () {
  // when ellipse is in the left edge, control would be/become false
  if (i==30) {
    control = false;
  }
  // if ellipse is inside the canvas width (we substract 30 which is the radius
  // of our ellipse) and control is false
  if (i<(width-30) && control==false){
    // state fill and alpha of the ellipse
    fill(146,87,67,40);
    //state stroke color and transparency
    stroke(234,65,88,5);
    i++
    // increase its x position (ellipse moves in the right direction)
    ellipse(i,height/2,60);
  }
  else {
    // else control will change to true
    control = true;
    //change the color and fill of the ellipse
    // state fill and alpha of the ellipse
    fill(56,57,67,100);
    //state stroke color and transparency
    stroke(5,165,188,50);
    // decrease its x position (ellipse moves in the left direction)
    i--;
    ellipse(i,height/2,60);
  }
}

Do a Git commit with the message "Alpha value".

• See more about the alpha() function