171 lines
6.9 KiB
Racket
171 lines
6.9 KiB
Racket
#lang scribble/doc
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@require["common.ss"]
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@defclass/title[bitmap-dc% object% (dc<%>)]{
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A @scheme[bitmap-dc%] object allows drawing directly into a bitmap. A
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@scheme[bitmap%] object must be supplied at initialization or
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installed into a bitmap DC using @method[bitmap-dc% set-bitmap]
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before any other method of the DC is called, except @method[dc<%>
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get-text-extent], @method[dc<%> get-char-height], or @method[dc<%>
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get-char-width]. If any other @scheme[bitmap-dc%] method is called
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before a bitmap is selected, the method call is ignored.
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Drawing to a @scheme[bitmap-dc%] with a color bitmap is guaranteed to
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produce the same result as drawing into a @scheme[canvas%] instance
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(with appropriate clipping and offsets). Thus, a @scheme[bitmap-dc%]
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can be used for offscreen staging of canvas content.
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@defconstructor[([bitmap (or/c (is-a?/c bitmap%) false/c)])]{
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Creates a new memory DC. If @scheme[bitmap] is not @scheme[#f], it is
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installed into the DC so that drawing commands on the DC draw to
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@scheme[bitmap]. Otherwise, no bitmap is installed into the DC and
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@method[bitmap-dc% set-bitmap] must be called before any other method
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of the DC is called.
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}
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@defmethod[(draw-bitmap-section-smooth [source (is-a?/c bitmap%)]
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[dest-x real?]
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[dest-y real?]
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[dest-width (and/c real? (not/c negative?))]
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[dest-height (and/c real? (not/c negative?))]
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[src-x real?]
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[src-y real?]
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[src-width (and/c real? (not/c negative?))]
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[src-height (and/c real? (not/c negative?))]
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[mask (or/c (is-a?/c bitmap%) false/c)])
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boolean?]{
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Display part of a bitmap with smooth scaling. For most platforms, this
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method produces better results than adjusting the scale of a drawing
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context before using @method[dc<%> draw-bitmap] and @method[dc<%>
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draw-bitmap-section], but this method is much slower.
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}
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@defmethod[(get-argb-pixels [x real?]
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[y real?]
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[width (integer-in 1 10000)]
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[height (integer-in 1 10000)]
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[pixels (and/c bytes? (not/c immutable?))]
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[alpha? any/c @scheme[#f]])
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void?]{
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Gets a rectangle of pixels in the bitmap, subject to the same rules
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and performance characteristics of @method[bitmap-dc% get-pixel],
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except that the block get is likely to be faster than the sequence of
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individual gets. Also, the @scheme[bitmap%] class also provides the
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same method directly, so it is not necessary to select a bitmap into
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a DC to extracts its pixel values.
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The pixel RGB values are copied into @scheme[pixels]. The first byte
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represents an alpha value of the pixel at (@scheme[x], @scheme[y]),
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the second byte represents a red value of the pixel at (@scheme[x],
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@scheme[y]), the third byte is the blue value, etc. In this way, the
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first @math{@scheme[width] * @scheme[height] *4} bytes of
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@scheme[pixels] are set to reflect the current pixel values in the
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DC. The pixels are in row-major order, left to right then top to
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bottom.
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If @scheme[alpha?] is false, then the alpha value for each pixel is
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set to 255. If @scheme[alpha?] is true, then @italic{only} the alpha
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value is set for each pixel, based on each pixel's value. Thus, the
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same @scheme[pixels] byte string is in general filled from two bitmaps:
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one (the main image) for the pixel values and one (the mask) for the
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alpha values.
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}
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@defmethod[(get-bitmap)
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(or/c (is-a?/c bitmap%) false/c)]{
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Gets the bitmap currently installed in the DC, or @scheme[#f] if no
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bitmap is installed. See @method[bitmap-dc% set-bitmap] for more
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information.
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}
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@defmethod[(get-pixel [x real?]
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[y real?]
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[color (is-a?/c color%)])
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boolean?]{
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Fills @scheme[color] with the color of the current pixel at position
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(@scheme[x], @scheme[y]) in the drawing context. If the color is
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successfully obtained, the return value is @scheme[#t], otherwise the
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result is @scheme[#f].
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Under X, interleaving drawing commands with @method[bitmap-dc%
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get-pixel] calls (for the same @scheme[bitmap-dc%] object) incurs a
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substantial performance penalty, except for interleaved calls to
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@method[bitmap-dc% set-pixel], @method[bitmap-dc% set-argb-pixels],
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and @method[bitmap-dc% get-argb-pixels].
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}
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@defmethod[(set-argb-pixels [x real?]
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[y real?]
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[width (integer-in 1 10000)]
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[height (integer-in 1 10000)]
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[pixels bytes?]
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[alpha? any/c @scheme[#f]])
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void?]{
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Sets a rectangle of pixels in the bitmap, subject to the same
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rules and performance characteristics of
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@method[bitmap-dc% set-pixel], except that the block set is likely to be faster than the
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sequence of individual sets.
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The pixel RGB values are taken from @scheme[pixels]. The first byte
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represents an alpha value, the second byte represents a red value to
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used for the pixel at (@scheme[x], @scheme[y]), the third byte is a blue
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value, etc. In this way, the first
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@math{@scheme[width] * @scheme[height] * 4} bytes of @scheme[pixels]
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determine the new pixel values in the DC. The pixels are in row-major
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order, left to right then top to bottom.
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If @scheme[alpha?] is false, then the alpha value for each pixel is
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ignored. If @scheme[alpha?] is true, then @italic{only} the each
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pixel is set based @italic{only} on the alpha value. Thus, the same
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@scheme[pixels] byte string is in general used with two bitmaps, one
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(the main image) for the pixel values and one (the mask) for the
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alpha values.
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}
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@defmethod[(set-bitmap [bitmap (or/c (is-a?/c bitmap%) false/c)])
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void?]{
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Installs a bitmap into the DC, so that drawing operations on the bitmap
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DC draw to the bitmap. A bitmap is removed from a DC by setting the
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bitmap to @scheme[#f].
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A bitmap can be selected into at most one bitmap DC, and only when it
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is not used by a control (as a label) or in a @scheme[pen%] or
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@scheme[brush%] (as a stipple). If the argument to @method[bitmap-dc%
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set-bitmap] is already in use by another DC, a control, a
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@scheme[pen%], or a @scheme[brush%], @|MismatchExn|.
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}
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@defmethod[(set-pixel [x real?]
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[y real?]
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[color (is-a?/c color%)])
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void?]{
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Sets a pixel in the bitmap.
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The current clipping region might not affect the pixel change. Under
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X, interleaving drawing commands with @method[bitmap-dc% set-pixel]
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calls (for the same @scheme[bitmap-dc%] object) incurs a substantial
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performance penalty, except for interleaved calls to
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@method[bitmap-dc% get-pixel], @method[bitmap-dc% get-argb-pixels],
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and @method[bitmap-dc% set-argb-pixels].
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}}
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