PHP

Since my last visit to this subject I have been thinking about how to represent a collection of random colours so that it looks sorted and that no information is lost during that process. I quickly realised that I needed to use all three aspects of the colour space, which lends itself to generating 3D objects. Indeed, the red, green, blue colour space is built around a cube so it can often be represented as a cube.

The hue, saturation, and value colour space is built around the concept of a cylinder, which means that 2 of the axis lend themselves to a circumference of a circle (the hue) and the diameter of a circle (the saturation). This is an example of the polar coordinate system. We can therefore draw a circle using hue and saturation and the value can be used to represent a different aspect of the colour space.

Since my last post, where I talked about drawling a line with pixels in PHP, I have been looking at drawing circles. As it turns out, there are a few different ways to draw a circle, so I'll go through a few options here.

To start with, there are some built in functions in PHP that can be used to draw an arc, circle or ellipse as a filled in shape or a line. The built in function in PHP called imageellipse() that can be used to draw a circle. This is part of the GD library.

Colourising images is fairly simple to accomplish, especially using PHP's GD library. All we need to do is load an image, create a blank image of the same size in a particular colour and then merge the two images together.

In fact, we can do this entirely with the imagecopymerge() function, but creating a function to wrap all of this makes sense as well.

The following function takes an image resource (as created by imagecreatefrompng()), the red, green, and blue values of the colour, and the percentage to overlay the colour on top of the image. The percentage can be set to 0 for no effect and 100 to fully replace the image with the given colour.

From the drawers of "I didn't realise how complicated that was" I was wondering the other day how to draw a line using just pixels. This turned out to be more complicated than I thought.

Normally in PHP you would use the imageline() function to draw a line between two points. The following block of code creates and image and draws a white line from the coordinates 50x,50y to 200x,150y.

// Generate image resource with a width an height of 250 pixels.
$im = imagecreatetruecolor(250, 250);

// Create a colour.
$white = imagecolorallocate($im, 255, 255, 255);

// Draw a white line from 50x,50y to 200x,150y.
imageline($im, 50, 50, 200, 150, $white);

// Write the image resource to a file called line.png.
imagepng($im, 'line.png');

// Destroy the image resource.
imagedestroy($im);

This creates an image that looks like this.

Following on from by previous post about sorting colours I decided to take another step towards sorting colours by segmenting the data to create a further dimension to the multi-dimensional array.

The array is already split into segments based on the hue of the colour, but we can further split this by separating out saturation and value into separate arrays within hue. To do this we set the saturation or value to be a constant and push them into separate arrays.

The new code looks like this. Please excuse the duplication of code here. This is just a simple example to show how the array is put together.

The last time I looked at sorting colours I had produced a nice band or sorted colours, but to do so I had essentially removed a third of the data from the colour information. This meant that there was no white or black colours in the band of sorted colours.

After a bit of thinking on how to solve this I hit upon a way of using a two dimensional array of colours to filter the colours into blocks. This would allow the missing colour information to be rendered correctly, and would only mean a small amount of work to allow it to work with the rendering function used in the previous examples.

Generating The Data

I could easily just generate every colour available and use that as the data. What I wanted to generate was a random assortment of colours that would represent the sort of data being produced by a system or other input.

SOLID is a set of object oriented design principles aimed at making code more maintainable and flexible. They were coined by Robert "Uncle Bob" Martin in the year 2000 in his paper Design Principles and Design Patterns. The SOLID principles apply to any object oriented language, but I'm going to concentrate on what they mean in a PHP application in this post.

I've been using PHP for a number of years and have seen the same things being done with return values from functions over and over again. I have always thought of this as pretty standard, but the more I think about it the less it makes sense. Looking back over my career I am quite sure that a few serious bugs could have been avoided if I had not mixed return types.

As PHP is a loosely typed language this gives the developers the ability to change the type of value that is returned from a function. This happens quite often within the PHP codebase itself as many built in functions will return false if an error happened.

A common practice in userland code is to return false from a function if something went wrong. This might be because it is encouraged in PHP itself.

I wanted to impart a piece of advice to do with validation and formatting of user input, although I've never seen anyone suggest it. I guess it would come under the single responsibility principle so it might seem obvious to some people. There can be reasons why this might at least seem like a good idea at the time.

Essentially, if you want to validate that something is correct, don't format it at the same time. These two actions should be done in separate functions or even classes. I hope to demonstrate that using a single function validate and format anything is a bad idea. I'll mainly be using PHP to demonstrate this, but the principle should be pretty much the same in any language.

Take the following function called isValid(). This is an arbitrary and simple example but shows validation and formatting in use in a single function.

Following on from my last post about sorting colours I have been thinking about different ways of sorting colours. I have been looking at interfaces that allow people to select colours and they will quite normally have a band of colours that does look nicely sorted. As it turns out this is perfectly possible to do if the colours are normalised to remove light and dark variations of different colours.

The easiest way to remove different amounts of lightness and darkness from a colour is to convert it to the HSV colour space. This way we can just set the value (brightness) and saturation (amount of grey) to be 1. This will change the colour by simply removing any information that does not pertain to the actual colour. For example, a colour that is a very light shade of blue will be changed to be simply blue.