Composing Images

image.ss

This teachpack provides primitives for constructing and manipulating images. These functions create basic shapes. The mode can be either 'solid, meaning the shape is filled in, or 'outline, meaning the shape is hollow. Colors can be either strings, symbols, or color structs (see below).

rectangle : int int mode image-color -> image
to create an image of a rectangle using the given width, height, mode, and color

circle : int mode image-color -> image
to create an image of a circle using the given radius, mode, and color

ellipse : int int mode image-color -> image
to create an image of an ellipse using the given width, height, and color

triangle : int mode iamge-color -> image
to create an equilateral triangle using the given edge size and color

line : int int image-color -> image
to create an image with a colored line from (0,0) to the point with the given coordinates

add-line : image int int int int image-color -> image
to add a line to an existing image, drawn between the two given points

text : string size image-color -> image
to create an image from the given string, point size, and background color

These functions build more complex images from the basic shapes. When two images are laid on top of each other, the are lined up at their pinhole. Most shapes have their pinholes right in the middle. The exceptions are text and line which have their pinholes in the top-left corner.

overlay : image image image ... -> image
to add the pixels of the second image onto the first image, lining up the pinholes

overlay/xy : image int int image -> image
to add the pixels of the second image onto the first image, lining up down and to the right of the first image's pinhole

After an image has been built up using overlays, it is possible to recover the position of the pieces of the image, using the next two functions.

image-inside : image image -> boolean
to determine whether the pixels of the second image appear in the first

find-image : image image -> posn
to determine where the pixels of the second image appear in the first

The rest of this teachpack are supplementary functions for manipulating images and colors.

image-color? : anything -> boolean
to determine if the input names a valid color.

image-width : image -> number
to obtain an image's width in pixels

image-height : image -> number
to obtain an image's height in pixels

image->color-list : image -> list-of-color
to convert an image to a list of colors

color-list->image : list-of-color int int -> image
to convert a list of colors to an image with the given width and height

make-color : int int int -> color
to construct a color

color? : anything -> boolean
to determine if its input is a color

color-red : color -> int
to extract the red component of a color

color-green : color -> int
to extract the green component of a color

color-blue : color -> int
to extract the blue component of a color

image->alpha-color-list : image -> list-of-alpha-color
to convert an image to a list of alpha colors

alpha-color-list->image : list-of-alpha-color int int -> image
to convert a list of alpha colors to an image with the given width and height"

make-alpha-color : int int int int -> color
to construct an alpha color

alpha-color? : anything -> boolean
to determine if its input is a color

alpha-color-alpha : color -> int
to extract the alpha value of a color

alpha-color-red : color -> int
to extract the red component of a color

alpha-color-green : color -> int
to extract the green component of a color

alpha-color-blue : color -> int
to extract the blue component of a color"