▼ |  | 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 | Matrix Snip
16 | Te X Table
17 | 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.rkt" teachpack. Images in the "image.rkt" 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.

> class

> 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.

> > > method

> > > ( 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.

> > > method

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

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

> > > method

> > > ( 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

> > > method

> > > ( 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.

> > > method

> > > ( 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.

> > > method

> > > ( 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.

> > > method

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

> > > →

> > > real? |  | real?

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

> > > method

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

> > →

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

> Returns the width and height for the image.

> > > method

> > > ( 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.

> > value

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

This snipclass is used for saved cache image snips.

> > procedure

> > ( make-argb vectorof width height) → argb?

> vectorof : byte?
> width : exact-nonnegative-integer?
> height : exact-nonnegative-integer?

Constructs a new argb value with the given width and height, using the data in the vector. The vector has four entries for each pixel, an alpha, red, green, and blue value. The pixels are specified in row-major order, so that the pixel at location (x,y) comes from vector entry (4*(x+(width*y))).

> > procedure

> > ( argb-vector argb) → ( vectorof byte? )

> argb : argb?

Extracts the vector from argb. The resulting vector has entries in row-major order, so that the data for the pixel at (x,y) winds up in four vector entries beginning at (4*(x+(width*y))).

> > procedure

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

> argb : argb?

Extracts the width from argb.

> > procedure

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

> argb : argb?

Extracts the height from argb.

> > procedure

> > ( argb? v) → boolean?

> v : any/c

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

> > procedure

> > ( 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.

> > procedure

> > ( 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<%>.

> > procedure

> > ( 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.

> > procedure

> > ( 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.

> > procedure

> > ( 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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