PeasyGradients is a library for Processing that makes drawing color gradients easy-peasy. This library was inspired by Jeremy Behreandt's Color Gradients in Processing but has greatly developed the concepts and functionality presented there.

This README provides an overview of the library — what it's capable of and how to use it. Access examples (Processing sketches) here; access documentation (online Javadocs) here.

• 11 Gradient Types

• 12 Color Spaces

• 14 Color Interpolation Functions

• Fast!

The PeasyGradients class renders 1D Gradients as 2D spectrums in your Processing sketch. A 1D Gradient consists solely of color stops — these define the colors and the discrete position (percentage) each color occurs at on the 1D axis.

A simple black-to-white gradient is created as such:

Gradient blackToWhite = new Gradient(color(0), color(255));

Here, blackToWhite is a 1D gradient with two equidistant color stops — black is at 0.00, and white is at 1.00.

Merely instantiating a 1D gradient doesn't draw anything. How should this 1D spectrum be drawn? Do we want to render a black-to-white linear gradient? A radial gradient? Or something else? This is where the PeasyGradients class comes in... We pass a Gradient (here, the blackToWhite 1D gradient) to one of a variety of methods to draw a 2D gradient.

PeasyGradients peasyGradients;

void setup() {
    peasyGradients = new PeasyGradients(this);
}

void draw() {
    peasyGradients.linearGradient(blackToWhite, 0); // angle = 0 (horizontal)
}

That's it! Now a horizontal black-to-white linear gradient will be drawn in the sketch (by default, the library draws directly into the sketch; you can give it a specific PGraphics pane to draw into with the .setRenderTarget() method).

See the Gradients section below for a showcase of each (2D) gradient type.

PeasyGradients provides methods to render 11 types of 2D gradients.

Zoom and rotation can be adjusted for most gradient types; certain gradient types offer additional parameters — for example, the polygon gradient requires a parameter specifying the number of polygon sides.

For many of the gradient types, there are multiple methods available to call, offering varying degrees of customisation of the gradient's spectrum shape.

Each gradient type is shown below. The screenshots are taken using the LUV color space with SMOOTH_STEP interpolation, and rotation set to 0 where applicable.

Linear	Radial
Conic	Spiral
Diamond	Cross
Polygon (n-sided)	Hourglass
Noise	Fractal Noise
Spotlight

In the parts of a Gradient between color stops, colors are composed via interpolating the neighbouring two color stops. Easing functions affect how these two adjacent stops contribute to the color of each point between them.

For example, with linear interpolation, a point in a Gradient which is midway between 2 color stops is composed of 50% of the first color and 50% of the second color — there is a linear relationship between its position and the weighting of color it receives from each color stop. Other easing functions are non-linear (for example a point closer to one color stop may in some cases receive more color from the second color stop) which can result in more interesting gradients.

Certain easing functions suit some gradient types better than others — for example, the BOUNCE function works well with polygon gradients but rather more poorly with linear gradients. Therefore, and as with color spaces, experimentation with different interpolation functions is encouraged.

Set the interpolation (easing) function for a given Gradient with .setInterpolationMode(), like so:

myGradient.setInterpolationMode(Interpolation.SMOOTH_STEP);

See for a comparison of all available easing functions modes in expandable section below:

💥See Interpolation Comparison...

Linear	Identity
Smooth Step	Smoother Step
Exponential	Cubic
Circular	Bounce
Sine	Parabola
Gain 1	Gain 2
Exponential Impulse	Heartbeat

Color spaces define how the color value at each color stop is represented.

Remember that a 1D Gradient consists of only a few defined color stops; all other colors in a Gradient's spectrum are composed by interpolating between any two adjacent color stops. Representing color stops differently (in different color spaces) affects the results of interpolation, and this can have a noticeable effect on the overall spectrum of a gradient (so experimentation with different color spaces is encouraged). A rule of thumb: avoid the RGB, RYB and HSB color spaces as they don't interpolate luminosity well.

Set the color space for a given Gradient with .setColorSpace(), like so:

myGradient.setColorSpace(ColorSpace.RGB);

PeasyGradients supports many different color spaces — all possible color spaces are accessible via ColorSpace.class and examples of each are shown in the expandable section below:

💥See Color Space Comparison...

Note that with the chosen gradient, the spectrum differences aren't too apparent between many of the colorspaces in the images below. Other gradients (i.e. using different colors) may exhibit more substantial differences between the different colorspaces.

RGB	RYB
HSB	XYZ (CIE 1931)
LAB (CIE L*a*b*)	HLAB (Hunter LAB)
DLAB	ITP (ICtCp)
LUV (CIE 1976 L*, u*, v*)	JAB (JzAzBz)
XYB	IPT

The position of all color stops within a Gradient can be offset using .setOffset(amount).

Furthermore, the .animate(amount) method changes this offset by the given amount each time it is called; with this you can create an gradient spectrum scrolling effect by calling .animate(0.01f) each frame for example.

Naively animating a gradient may lead to an ugly and undesirable seam in the gradient where the first and last color stops (at positions 0.00 and 1.00 respectively) bump right up against each other, like in the linear gradient below:

To avoid this, call .primeAnimation() on a Gradient (once) before animating it. This pushes a copy of the first color stop of the Gradient to its end (scaling all other color stops accordingly), to ensure a seamless gradient spectrum, regardless of offset.

Calling .primeAnimation() on a Gradient before rendering it as a conic or spiral gradient has the added benefit of smoothing the transition between the first and last colors, regardless of whether you wish to animate the gradient, as below:

The color of Colorstops within a Gradient can be modified after the Gradient has been instantiated.

Set the color of a specific color stop with .setStopColor(), shown below:

angle  = PI / 180; // increment angle

colorMode(HSB, 360, 100, 100); // switch Processing to HSB mode to set hue more easily

myGradient.setStopColor(0, color(frameCount % 360, 100, 100)); // set color stop at index 0
myGradient.setStopColor(1, color((frameCount   180) % 360, 100, 100)); // set color stop at index 1

peasyGradients.linearGradient(myGradient, angle); // render gradient

The position of Colorstops within a Gradient can also be modified after the Gradient has been instantiated.

Set the position (0...1.0) of a specific color stop with .setStopPosition(), shown below:

myGradient.setStopPosition(1, map(mouseX, 0, width, 0, 1)); // set position of middle color (index = 1)

peasyGradients.linearGradient(myGradient, 0);

Use posterisation to define the maximum number of colors the PeasyGradient renderer uses to render Gradients. Smaller numbers are more restrictive and increase the color banding effect — there may be times when this artistic effect is desirable.

peasyGradients.posterise(10); // renderer will now render gradients with 10 colors at most 

No Posterisation (default)	Posterisation = 10	Posterisation = 25

Use .clearPosterisation() to clear any posterisation setting and render gradients with in full color.

The Palette class provides some helper methods for generating random Gradient color palettes.

Note this palette generation is not entirely random -- the class produces gradients spectrums that are more aesthetic than what a truly random method would generate.

randomGradient = new Gradient(Palette.complementary()); // two random colors that are on opposite sides of the color wheel
randomGradient = new Gradient(Palette.triadic()); // 3 random colors that are evenly spaced on the color wheel
randomGradient = new Gradient(Palette.tetradic()); // 4 random colors that are evenly spaced on the color wheel
randomGradient = new Gradient(Palette.randomcolors(7)); // N random colors with hue distributed according to the golden ratio
randomGradient = new Gradient(Palette.randomRandomcolors(8)); // N random colors also distributed randomly

Strictly speaking, this functionality isn't defined by PeasyGradients (rather, it's defined by Processing itself). But I think it's worthwhile to show how masking can be used in conjunction with PeasyGradients. An example which uses text ("P") to mask a spiral gradient is provided below:

void setup() {

  gradientLayer = createGraphics(WIDTH, HEIGHT); // PGraphics layer containing gradient
  textLayer = createGraphics(WIDTH, HEIGHT); //  PGraphics layer containing text (used as alpha mask)

  peasyGradients = new PeasyGradients(this);

  textLayer.beginDraw();
  textLayer.fill(255); // set to white to set pixels to keep during alpha mask
  textLayer.textSize(150);
  textLayer.textAlign(CENTER, CENTER);
  textLayer.text("N", width / 2, height / 2 - textLayer.textDescent() / 2); // draw text in image center
  textLayer.endDraw();
}

void draw() {

  PVector mousePos = new PVector(mouseX, mouseY);

  background(0);
  
  // render gradient into PGraphics layer
  peasyGradients.setRenderTarget(gradientLayer);
  peasyGradients.spiralGradient(gradient, mousePos, map(mouseY, 0, height, 0.5f, PI * 6), 2); // map spiral rotation to mouse position
  gradientLayer.mask(textLayer.get()); // mask gradient layer using text (keep only the text)

  image(gradientLayer, 0, 0); // draw (now masked) gradient image
}

PeasyGradients targets the CPU (as opposed to the GPU) as to not be dependent on OPENGL libraries. To this end, there have been many internal optimisations to make the library suitable for dynamic animation and interaction rather than just static rendering. Care was taken to optimise color interpolation and gradient rasterization, and finally multithreading was added to naively parallelise the workload. Therefore, rendering (most) gradients at 60fps at high resolutions (1080p ) is more than achievable on modern processors.

• Implement four-corner gradients (or a more general form which distributes N colors, placing them around the edge and interpolating towards the middle).
• Implement this type of spiral gradient.
• Allow easing functions to be passed in to render methods to affect the curve of whole spectrum not just the curve between each successive pair of color stops.
• Add preset color scales (rainbow, warm, cool, etc.) to Palettes.
• Add a gradient contour plot overlay feature.
• Implement the CAM16/CAM16‐UCS Color Appearance Model as a colorspace.