How it all works

The script img.php uses the class CImage which carries out all the image processing, caching and delivery of the resulting image. img.php takes the incoming query string and prepares all the parameters and then uses the public API of CImage.

#The programmatic flow

This is how you can get an understanding on how CImage processes the image.

Review the settings in webroot/img_config.php and check out webroot/img.php on how it uses CImage.

The programmatic flow, just to get you oriented in the environment, is like this.

1. Start in img.php.
2. img.php reads configuration details from img_config.php (if the config-file is available).
3. img.php reads and processes incoming $_GET arguments to use as options while prepare using CImage.
4. img.php uses CImage.
5. CImage processes, caches and outputs the image according to the options used.

#How img.php uses the class CImage

This is a simplified view on how img.php uses the class CImage.

/**
 * Create the class for the image.
 */
require $config['cimage_class'];

$img = new CImage();
$img->setVerbose($verbose);

/**
 * Load, process and output the image
 */
$img->log("Incoming arguments: " . print_r(verbose(), 1))
    ->setSaveFolder($cachePath)
    ->useCache($useCache)
    ->setSource($srcImage, $imagePath)
    ->setOptions(
        array(
            // Options for calculate dimensions
            'newWidth'  => $newWidth,
            'newHeight' => $newHeight,
            'aspectRatio' => $aspectRatio,
            'keepRatio' => $keepRatio,
            'cropToFit' => $cropToFit,
            'fillToFit' => $fillToFit,
            'crop'      => $crop,
            'area'      => $area,
            'upscale'   => $upscale,

            // Pre-processing, before resizing is done
            'scale'        => $scale,
            'rotateBefore' => $rotateBefore,
            'autoRotate'   => $autoRotate,

            // General processing options
            'bgColor'    => $bgColor,

            // Post-processing, after resizing is done
            'palette'   => $palette,
            'filters'   => $filters,
            'sharpen'   => $sharpen,
            'emboss'    => $emboss,
            'blur'      => $blur,
            'convolve'  => $convolve,
            'rotateAfter' => $rotateAfter,

            // Output format
            'outputFormat' => $outputFormat,
            'dpr'          => $dpr,
        )
    )
    ->loadImageDetails()
    ->initDimensions()
    ->calculateNewWidthAndHeight()
    ->setSaveAsExtension($saveAs)
    ->setJpegQuality($quality)
    ->setPngCompression($compress)
    ->useOriginalIfPossible($useOriginal)
    ->generateFilename($cachePath)
    ->useCacheIfPossible($useCache)
    ->load()
    ->preResize()
    ->resize()
    ->postResize()
    ->setPostProcessingOptions($postProcessing)
    ->save()
    ->linkToCacheFile($aliasTarget)
    ->output();

THe script img.php may also use CImage to set the default background color and add convolution expressions, but it depends on if the values are set in the config file img_config.php. It can look like this:

$img->setDefaultBackgroundColor($config['background_color']);
$img->addConvolveExpressions($config['convolution_constant']);