▼ |  | Mr Lib: Extra GUI Libraries

1 | Aligned Pasteboard
2 | Bitmap Label
3 | Cache-image Snip
4 | Close Icon
5 | GIF and Animated GIF Writing
6 | Graphs
7 | Hierarchical List Control
8 | Include Bitmap
9 | Interactive Value Port
10 | Name Message
11 | Path Dialog
12 | Plot
13 | Switchable Button
14 | Image Core
15 | Te X Table
16 | Acknowledgments
| Index

On this page:

cache-image-snip%
equal-to?
get-argb
get-argb-proc
get-argb/ no-compute
get-bitmap
get-dc-proc
get-pinhole
get-size
other-equal-to?
snip-class
make-argb
argb-vector
argb-width
argb-height
argb?
overlay-bitmap
build-bitmap
flatten-bitmap
argb->cache-image-snip
argb->bitmap

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### 3`` Cache-image Snip

( require mrlib/cache-image-snip )

The mrlib/cache-image-snip library provides the core data structure for DrRacket’s "image.ss" teachpack. Images in the "image.ss" teachpack are instances of the cache-image-snip% class.

The library also defines a new type, argb, that represents a bitmap, but with alpha values. It has a maker, two selectors, and a predicate.

cache-image-snip% : class?
superclass: image-snip%

The cache-image-snip% class is a subclass of image-snip% simply so that its instances can be compared with image-snip% using equal?. All image-snip% functionality is overridden or ignored.

> ( send a-cache-image-snip equal-to? |  | snip |  |  |  |
> |  | equal?) |  | → |  | boolean?

> snip : ( is-a?/c image-snip% )
> equal? : ( any/c any/c . -> . boolean? )

> Calls the other-equal-to? method of snip if it is also a cache-image-snip% instance, otherwise calls the other-equal-to? of a-cache-image-snip.

> ( send a-cache-image-snip get-argb ) → argb?

> Returns a pixel array for this image, forcing it to be computed.

> ( send a-cache-image-snip get-argb-proc )
> → ( argb? exact-integer? exact-integer? . -> . void? )

> Returns a procedure that fills in an argb with the contents of this image at the given offset

> ( send a-cache-image-snip get-argb/no-compute )
> → ( or/c false/c argb? )

> Returns a pixel array for this image or #f if it has not been computed yet.

> ( send a-cache-image-snip get-bitmap )
> → ( or/c false/c ( is-a?/c bitmap% ))

> Overrides get-bitmap in image-snip%.
> Builds (if not yet built) a bitmap corresponding to this snip and returns it.

> If the width or the height of the snip is 0, this method return #f.

> ( send a-cache-image-snip get-dc-proc )
> → ( or/c false/c (( is-a?/c dc<%> ) real? real? -> void? ))

> Either returns false, or a procedure that draws the contents of this snip into a dc.

> ( send a-cache-image-snip get-pinhole )

> →

> real? |  | real?

> Returns the pinhole coordinates for this image, counting from the top-left of the image.

> ( send a-cache-image-snip get-size )

> →

> exact-nonnegative-integer?
> exact-nonnegative-integer?

> Returns the width and height for the image.

> ( send a-cache-image-snip other-equal-to? |  | snip |  |  |  |
> |  | equal?) |  | → |  | boolean?

> snip : ( is-a?/c image-snip% )
> equal? : ( any/c any/c . -> . boolean? )

> Overrides other-equal-to? in image-snip%.
> Refines the comparison of other-equal-to? in image-snip% to exactly match alpha channels.

snip-class : ( is-a?/c snip-class% )

This snipclass is used for saved cache image snips.

( make-argb vectorof width height) → argb?
vectorof : ( integer-in 0 255)
width : exact-nonnegative-integer?
height : exact-nonnegative-integer?

Constructs a new argb value. The vector has four entries for each pixel, an alpha, red, green, and blue value. The int specifies the width of the image; the height is the size of the vector, divided by 4, divided by the width.

( argb-vector argb) → ( vectorof ( integer-in 0 255))
argb : argb?

Extracts the vector from argb.

( argb-width argb) → exact-nonnegative-integer?
argb : argb?

Extracts the width from argb.

( argb-height argb) → exact-nonnegative-integer?
argb : argb?

Extracts the height from argb.

( argb? v) → boolean?
v : any/c

Returns #t if v is an argb, #f otherwise.

( overlay-bitmap dest dx dy img mask) → void?
dest : argb?
dx : exact-integer?
dy : exact-integer?
img : ( is-a?/c bitmap% )
mask : ( is-a?/c bitmap% )

Changes argb, overlaying img with masking based on mask at (dx, dy) from the top-left.

( build-bitmap draw width height) → ( is-a?/c bitmap% )
draw : (( is-a?/c dc<%> ) . -> . any )
width : ( integer-in 1 10000)
height : ( integer-in 1 10000)

Builds a bitmap of size width by height, using the procedure draw to render the bitmap content into the given dc<%>.

( flatten-bitmap bitmap) → ( is-a?/c bitmap% )
bitmap : ( is-a?/c bitmap% )

Builds a new bitmap that flattens the original bitmap with its mask (as determined by get-loaded-mask in bitmap%), producing a bitmap that has no mask, and looks the way that bitmap would draw (when drawn with the mask) onto a white background.

( argb->cache-image-snip argb dx dy) → ( is-a?/c cache-image-snip% )
argb : argb?
dx : real?
dy : real?

Builds a new cache-image-snip% based on the contents of argb, using dx and dy as the pinhole.

( argb->bitmap argb) → ( or/c false/c ( is-a?/c bitmap% ))
argb : argb?

Builds a bitmap that draws the same way as argb; the alpha pixels are put into the bitmap’s get-loaded-mask bitmap.

If the width or height of argb is 0, this returns #f.

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