{ (define LIBNAME "Images") (include "head.tinc") } 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. Image colors can be either symbols (like 'blue), strings (like "blue"), or color structs (like (make-color 0 0 255)) -- see below for more information about color structs.
  • {(idx rectangle)} : int int mode image-color -> image
    to create a rectangle using the given width, height, mode, and color
  • {(idx circle)} : int mode image-color -> image
    to create a circle using the given radius, mode, and color
  • {(idx ellipse)} : int int mode image-color -> image
    to create an ellipse using the given width, height, and color
  • {(idx triangle)} : int mode iamge-color -> image
    to create an upward pointing equilateral triangle using the given edge size and color
  • {(idx line)} : int int image-color -> image
    to create an image with a colored line from (0,0) to the point with the given coordinates
  • {(idx add-line)} : image int int int int image-color -> image
    to add a line to an existing image, drawn between the two given points
  • {(idx text)} : string size image-color -> image
    to create an image of the text in the given string, with the point size, and color specified by the last two arguments
    • These functions build 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 in the middle. The exceptions are text and line which have their pinholes in the top-left corner.
  • {(idx overlay)} : image image image ... -> image
    to add the pixels of the second image onto the first image, lining up the pinholes
  • {(idx overlay/xy)} : image int int image -> image
    to add the pixels of the second image onto the first image. Instead of lining up on the pinhole, the second image's pinhole is lined up with an offset from the first image's pinhole. The two coordinates specify how far down and to the right the offset should be. The pinhole of the resulting image is the same place as the pinhole in the first image.
    • After an image has been overlaid on another, it is possible to recover the position of overlaid image, using the next two functions.
  • {(idx image-inside?)} : image image -> boolean
    to determine whether the pixels of the second image appear in the first

    Be careful when using this function with jpeg images. If you use an image-editing program to crop a jpeg image and then save it, image-inside? will not recognize the cropped image, due to jpeg's compression.

    Use png images instead.

  • {(idx find-image)} : image image -> posn
    to determine where the pixels of the second image appear in the first, with respect to the pinhole of the first image.
    • The shrink functions trim an image by eliminating extraneous pixels.
  • {(idx shrink-tl)} : image number number -> image
    to shrink the image, starting from the top-left corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.
  • {(idx shrink-tr)} : image number number -> image
    to shrink the image, starting from the top-right corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.
  • {(idx shrink-bl)} : image number number -> image
    to shrink the image, starting from the bottom-left corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.
  • {(idx shrink-br)} : image number number -> image
    to shrink the image, starting from the bottom-right corner. The two numbers indicate how many pixels to save. The pinhole of the resulting image is in the middle of the image.
  • {(idx shrink)} : image number number number number -> image
    to shrink an image around its pinhole. The numbers are the pixels to save to left, above, to the right, and below the pinhole, respectively. The pixel directly on the pinhole is always saved.
    • These functions provide information about the image's size.
  • {(idx image-width)} : image -> number
    to obtain an image's width in pixels
  • {(idx image-height)} : image -> number
    to obtain an image's height in pixels
    • This functions provide information and manipulate an image's pinhole.
  • {(idx pinhole-x)} : image -> number
    to determine the x coordinate of the pinhole, measuring from the left of the image
  • {(idx pinhole-y)} : image -> number
    to determine the y coordinate of the pinhole, measuring down from the left of the image
  • {(idx move-pinhole)} : image number number -> image
    to move the pinhole down and to the right (by the specified amounts) of its current location. Use negative numbers to move it up or to the left.
  • {(idx put-pinhole)} : image number number -> image
    to put the pinhole in the location specified by the arguments, counting from the left and down from the top, respectively.
    • This function precisely specifies what a valid image color is.
  • {(idx image-color?)} : anything -> boolean
    to determine if the input is a valid image color
    • The next functions separate an image into its consitiuent colors and combine pixels together to build an image.
  • {(idx image->color-list)} : image -> list-of-color
    to convert an image to a list of colors
  • {(idx color-list->image)} : list-of-color int int int int -> image
    to convert a list of colors to an image with the given width and height, and pinhole coordinates (the pinhole coordinates are with respect to the top-left of the image).
  • {(idx make-color)} : int int int -> color
    to construct a color
  • {(idx color?)} : anything -> boolean
    to determine if its input is a color
  • {(idx color-red)} : color -> int
    to extract the red component of a color
  • {(idx color-green)} : color -> int
    to extract the green component of a color
  • {(idx color-blue)} : color -> int
    to extract the blue component of a color
    • Like the last group of functions, these functions separate an image into its consitiuent colors and combine pixels together to build an image, but these provide alpha-channel information as well. Alpha channels are a measure of transparency; 0 indicates fully opaque and 255 indicates fully transparent.
  • {(idx image->alpha-color-list)} : image -> list-of-alpha-color
    to convert an image to a list of alpha colors
  • {(idx alpha-color-list->image)} : list-of-alpha-color int int int int -> image
    to convert a list of alpha colors to an image with the given width and height, and pinhole coordinates (the pinhole coordinates are with respect to the top-left of the image).
  • {(idx make-alpha-color)} : int int int int -> color
    to construct an alpha color
  • {(idx alpha-color?)} : anything -> boolean
    to determine if its input is a color
  • {(idx alpha-color-alpha)} : color -> int
    to extract the alpha value of a color
  • {(idx alpha-color-red)} : color -> int
    to extract the red component of a color
  • {(idx alpha-color-green)} : color -> int
    to extract the green component of a color
  • {(idx alpha-color-blue)} : color -> int
    to extract the blue component of a color"
    • {(include "foot.tinc")} {(include "foot.tinc")}