On this page:
flomap
flomap-size
flomap-ref
flomap-ref*
flomap-bilinear-ref
flomap-bilinear-ref*
flomap-min-value
flomap-max-value
flomap-extreme-values
flomap-nonzero-rect
coords->index
unsafe-flomap-ref
unsafe-flomap-ref*

4.2 Struct Type and Accessors🔗

struct

(struct flomap (values components width height))

  values : FlVector
  components : Integer
  width : Integer
  height : Integer
Represents a width×height floating-point bitmap with components color components. The values vector contains the flattened image data (see Data Layout).

A guard ensures that the values field has length (* components width height), and that each size field is a nonnegative fixnum.

Examples:
> (require racket/flonum)
> (flomap (flvector 0.0 0.0 0.0 0.0) 4 1 1)

(flomap (flvector 0.0 0.0 0.0 0.0) 4 1 1)

> (flomap (flvector) 0 0 0)

(flomap (flvector) 0 0 0)

> (flomap (flvector 0.0) 2 1 1)

flomap: expected flvector of length 2; given one of length 1

The default flomap constructor is perhaps the hardest to use. Instead, to construct a flomap from scratch, you should generally use make-flomap, make-flomap*, build-flomap or draw-flomap.

Returns the width and height of fm as nonnegative fixnums.

procedure

(flomap-ref fm k x y)  Float

  fm : flomap
  k : Integer
  x : Integer
  y : Integer
Returns fm’s value at k x y.

If x or y is out of bounds, this function returns 0.0. If k is out of bounds, it raises an error. The Conceptual Model section explains why k is treated differently.

procedure

(flomap-ref* fm x y)  FlVector

  fm : flomap
  x : Integer
  y : Integer
Returns fm’s component values at x y as an flvector.

If x or y is out of bounds, this function returns an flvector filled with 0.0. It always returns an flvector of length (flomap-components fm).

procedure

(flomap-bilinear-ref fm k x y)  Float

  fm : flomap
  k : Integer
  x : Real
  y : Real
Returns an estimated value at any given k x y coordinate, calculated from known values in fm.

Like all other flomap functions that operate on real-valued coordinates, flomap-bilinear-ref regards known values as being at half-integer coordinates. Mathematically, if x = (+ i 0.5) and y = (+ j 0.5) for any integers i and j, then (flomap-bilinear-ref fm k x y) = (flomap-ref fm k i j).

Suppose fm is size w×h. If x-0.5 or x(+ w 0.5), this function returns 0.0; similarly for y and h. If k is out of bounds, it raises an error. The Conceptual Model section explains why k is treated differently.

procedure

(flomap-bilinear-ref* fm x y)  FlVector

  fm : flomap
  x : Real
  y : Real
Like flomap-bilinear-ref, but returns an flvector containing estimates of all the components at x y.

procedure

(flomap-min-value fm)  Float

  fm : flomap

procedure

(flomap-max-value fm)  Float

  fm : flomap
These return the minimum and maximum values in fm.

procedure

(flomap-extreme-values fm)  
Float Float
  fm : flomap
Equivalent to (values (flomap-min-value fm) (flomap-max-value fm)), but faster.

Returns the smallest rectangle containing every nonzero value (in any component) in fm. The values returned are x minimum, y minimum, x maximum + 1, and y maximum + 1.

The values returned by flomap-nonzero-rect can be sent to subflomap to trim away zero values. But see flomap-trim, which is faster for alpha-multiplied flomaps.

procedure

(coords->index c w k x y)  Fixnum

  c : Integer
  w : Integer
  k : Integer
  x : Integer
  y : Integer
Returns the index of the value at coordinates k x y of a flomap with c color components and width w. This function does not check any coordinates against their bounds.

procedure

(unsafe-flomap-ref vs c w h k x y)  Float

  vs : FlVector
  c : Integer
  w : Integer
  h : Integer
  k : Integer
  x : Integer
  y : Integer
If fm = (flomap vs c w h), returns fm’s value at k x y. If x or y is out of bounds, this returns 0.0. It is unsafe because k is unchecked, as well as indexing into vs.

This function is used by some library functions, such as flomap-bilinear-ref, to index into already-destructured flomaps. From untyped code, applying this function is likely no faster than applying flomap-ref, because of extra contract checks.

procedure

(unsafe-flomap-ref* vs c w h x y)  FlVector

  vs : FlVector
  c : Integer
  w : Integer
  h : Integer
  x : Integer
  y : Integer
Like unsafe-flomap-ref, but returns an flvector containing all the component values at x y.