▼The Racket Drawing Toolkit
On this page:
draw-bitmap-section-smooth
get-argb-pixels
get-bitmap
get-pixel
set-argb-pixels
set-bitmap
set-pixel
Inherited methods:
from dc<%>
cache-font-metrics-key
clear
copy
draw-arc
draw-bitmap
draw-bitmap-section
draw-ellipse
draw-line
draw-lines
draw-path
draw-point
draw-polygon
draw-rectangle
draw-rounded-rectangle
draw-spline
draw-text
end-doc
end-page
erase
flush
get-alpha
get-background
get-brush
get-char-height
get-char-width
get-clipping-region
get-device-scale
get-font
get-gl-context
get-initial-matrix
get-origin
get-pen
get-rotation
get-scale
get-size
get-smoothing
get-text-background
get-text-extent
get-text-foreground
get-text-mode
get-transformation
glyph-exists?
ok?
resume-flush
rotate
scale
set-alpha
set-background
set-brush
set-clipping-rect
set-clipping-region
set-font
set-initial-matrix
set-origin
set-pen
set-rotation
set-scale
set-smoothing
set-text-background
set-text-foreground
set-text-mode
set-transformation
start-doc
start-page
suspend-flush
transform
translate
try-color
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bitmap-dc% : class?

  superclass: object%

  extends: dc<%>
A bitmap-dc% object allows drawing directly into a bitmap. A bitmap% object must be supplied at initialization or installed into a bitmap DC using set-bitmap before any other method of the DC is called, except get-text-extent, get-char-height, or get-char-width. If any other bitmap-dc% method is called before a bitmap is selected, the method call is ignored.

Drawing to a bitmap-dc% with a color bitmap is guaranteed to produce the same result as drawing into a canvas% instance (with appropriate clipping and offsets). Thus, a bitmap-dc% can be used for offscreen staging of canvas content.

(new bitmap-dc% [bitmap bitmap]) → (is-a?/c bitmap-dc%)
  bitmap : (or/c (is-a?/c bitmap%) false/c)
Creates a new memory DC. If bitmap is not #f, it is installed into the DC so that drawing commands on the DC draw to bitmap. Otherwise, no bitmap is installed into the DC and set-bitmap must be called before any other method of the DC is called.

(send a-bitmap-dc draw-bitmap-section-smooth source 
  dest-x 
  dest-y 
  dest-width 
  dest-height 
  src-x 
  src-y 
  src-width 
  src-height 
  mask) 
 → boolean?
  source : (is-a?/c bitmap%)
  dest-x : real?
  dest-y : real?
  dest-width : (and/c real? (not/c negative?))
  dest-height : (and/c real? (not/c negative?))
  src-x : real?
  src-y : real?
  src-width : (and/c real? (not/c negative?))
  src-height : (and/c real? (not/c negative?))
  mask : (or/c (is-a?/c bitmap%) false/c)
The same as draw-bitmap-section, except that dest-width and dest-height cause the DC’s transformation to be adjusted while drawing the bitmap so that the bitmap is scaled; and, if the DC’s smoothing mode is 'unsmoothed, it is changed to 'aligned while drawing.

(send a-bitmap-dc get-argb-pixels x    
  y    
  width    
  height    
  pixels    
  [just-alpha?    
  pre-multiplied?]) → void?
  x : real?
  y : real?
  width : exact-nonnegative-integer?
  height : exact-nonnegative-integer?
  pixels : (and/c bytes? (not/c immutable?))
  just-alpha? : any/c = #f
  pre-multiplied? : any/c = #f
Gets a rectangle of pixels in the bitmap, subject to the same rules and performance characteristics of get-pixel, except that the block get is likely to be faster than the sequence of individual gets. Also, the bitmap% class also provides the same method directly, so it is not necessary to select a bitmap into a DC to extracts its pixel values.

The pixel RGB values are copied into pixels. The first byte represents an alpha value of the pixel at (x, y), the second byte represents a red value of the pixel at (x, y), the third byte is the blue value, etc. In this way, the first width * height * 4 bytes of pixels are set to reflect the current pixel values in the DC. The pixels are in row-major order, left to right then top to bottom.

If just-alpha? is false, if the bitmap does not have an alpha channel, then the alpha value for each pixel is set to 255. If just-alpha? is true, then only the alpha value is set for each pixel; if the bitmap has no alpha channel, then the alpha value is based on each pixel’s inverted RGB average. Thus, when a bitmap has a separate mask bitmap, the same pixels byte string is in general filled from two bitmaps: one (the main image) for the pixel values and one (the mask) for the alpha values.

If pre-multiplied? is true, just-alpha? is false, and the bitmap has an alpha channel, then RGB values in the result are scaled by the corresponding alpha value (i.e., multiplied by the alpha value and then divided by 255).

(send a-bitmap-dc get-bitmap)
 → (or/c (is-a?/c bitmap%) false/c)
Gets the bitmap currently installed in the DC, or #f if no bitmap is installed. See set-bitmap for more information.

(send a-bitmap-dc get-pixel x y color) → boolean?
  x : real?
  y : real?
  color : (is-a?/c color%)
Fills color with the color of the current pixel at position (x, y) in the drawing context. If the color is successfully obtained, the return value is #t, otherwise the result is #f.

(send a-bitmap-dc set-argb-pixels x    
  y    
  width    
  height    
  pixels    
  [just-alpha?    
  pre-multiplied?]) → void?
  x : real?
  y : real?
  width : exact-nonnegative-integer?
  height : exact-nonnegative-integer?
  pixels : bytes?
  just-alpha? : any/c = #f
  pre-multiplied? : any/c = #f

Sets a rectangle of pixels in the bitmap, unless the DC’s current bitmap was produced by make-screen-bitmap or make-bitmap in canvas% (in which case an exn:fail:contract exception is raised).

The pixel RGB values are taken from pixels. The first byte represents an alpha value, the second byte represents a red value to used for the pixel at (x, y), the third byte is a blue value, etc. In this way, the first width * height * 4 bytes of pixels determine the new pixel values in the DC. The pixels are in row-major order, left to right then top to bottom.

If just-alpha? is false, then the alpha value for each pixel is used only if the DC’s current bitmap has an alpha channel. If just-alpha? is true and the bitmap has no alpha channel, then each pixel is set based only on the alpha value, but inverted to serve as a mask. Thus, when working with bitmaps that have an associated mask bitmap instead of an alpha channel, the same pixels byte string is used with two bitmaps: one (the main image) for the pixel values and one (the mask) for the alpha values.

If pre-multiplied? is true, just-alpha? is false, and the bitmap has an alpha channel, then RGB values in pixels are interpreted as scaled by the corresponding alpha value (i.e., multiplied by the alpha value and then divided by 255). If an R, G, or B value is greater than its corresponding alpha value (which is not possible if the value is properly scaled), then it is effectively reduced to the alpha value.

(send a-bitmap-dc set-bitmap bitmap) → void?
  bitmap : (or/c (is-a?/c bitmap%) false/c)
Installs a bitmap into the DC, so that drawing operations on the bitmap DC draw to the bitmap. A bitmap is removed from a DC by setting the bitmap to #f.

A bitmap can be selected into at most one bitmap DC, and only when it is not used by a control (as a label) or in a pen% or brush% (as a stipple). If the argument to set-bitmap is already in use by another DC, a control, a pen%, or a brush%, an exn:fail:contract exception is raised.

(send a-bitmap-dc set-pixel x y color) → void?
  x : real?
  y : real?
  color : (is-a?/c color%)
Sets a pixel in the bitmap.

The current clipping region might not affect the pixel change. Under X, interleaving drawing commands with set-pixel calls (for the same bitmap-dc% object) incurs a substantial performance penalty, except for interleaved calls to get-pixel, get-argb-pixels, and set-argb-pixels.

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