1Prima::ImageViewer(3) User Contributed Perl DocumentationPrima::ImageViewer(3)
2
6 Prima::ImageViewer - standard image, icon, and bitmap viewer class.
7 SYNOPSIS
9 use Prima qw(ImageViewer StdBitmap Application);
10 Prima::ImageViewer-> new(
11 image => Prima::StdBitmap::image(0),
12 zoom => 2.718,
13 );
14 run Prima;
15
17 The module contains "Prima::ImageViewer" class, which provides image
18 displaying functionality, including different zoom levels.
19 "Prima::ImageViewer" is a descendant of "Prima::ScrollWidget" and
21 inherits its document scrolling behavior and programming interface.
22 See Prima::ScrollWidget for details.
23
25 Properties
26 alignment INTEGER
27 One of the following "ta::XXX" constants:
28 ta::Left
30 ta::Center
31 ta::Right
32 Selects the horizontal image alignment.
34 Default value: "ta::Left"
36 autoZoom BOOLEAN
38 When set, the image is automatically stretched while keeping
39 aspects to the best available fit, given the "zoomPrecision".
40 Scrollbars are turned off if "autoZoom" is set to 1.
41 image OBJECT
43 Selects the image object to be displayed. OBJECT can be an instance
44 of "Prima::Image", "Prima::Icon", or "Prima::DeviceBitmap" class.
45 imageFile FILE
47 Set the image FILE to be loaded and displayed. Is rarely used since
48 does not return a loading success flag.
49 stretch BOOLEAN
51 If set, the image is simply stretched over the visual area, without
52 keeping the aspect. Scroll bars, zooming and keyboard navigation
53 become disabled.
54 quality BOOLEAN
56 A boolean flag, selecting if the palette of "image" is to be copied
57 into the widget palette, providing higher visual quality on
58 paletted displays. See also "palette" in Prima::Widget.
59 Default value: 1
61 valignment INTEGER
63 One of the following "ta::XXX" constants:
64 ta::Top
66 ta::Middle or ta::Center
67 ta::Bottom
68 Selects the vertical image alignment.
70 NB: "ta::Middle" value is not equal to "ta::Center"'s, however the
72 both constants produce equal effect here.
73 Default value: "ta::Bottom"
75 zoom FLOAT
77 Selects zoom level for image display. The acceptable value range is
78 between 0.01 and 100. The zoom value is rounded to the closest
79 value divisible by 1/"zoomPrecision". For example, is
80 "zoomPrecision" is 100, the zoom values will be rounded to the
81 precision of hundredth - to fiftieth and twentieth fractional
82 values - .02, .04, .05, .06, .08, and 0.1 . When "zoomPrecision" is
83 1000, the precision is one thousandth, and so on.
84 Default value: 1
86 zoomPrecision INTEGER
88 Zoom precision of "zoom" property. Minimal acceptable value is 10,
89 where zoom will be rounded to 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0 .
90 The reason behind this arithmetics is that when an image of an
92 arbitrary zoom factor is requested to be displayed, the image
93 sometimes must be drawn from a fraction image pixel - for example,
94 10x zoomed image shifted 3 pixels left, must be displayed so the
95 first image pixel from the left occupies 7 screen pixels, and the
96 next ones - 10 screen pixels. That means, that the correct image
97 display routine must ask the system to draw the image at offset -3
98 screen pixels, where the first image pixel column would correspond
99 to that offset.
100 When the zoom factor is fractional, the picture is getting more
102 complex. For example, with zoom factor 12.345, and zero screen
103 offset, the first image pixel begins at the 12th screen pixel, the
104 next one - at the 25th ( because of the roundoff ), then the 37th
105 etc etc. If the image is 2000x2000 pixels wide, and is asked to be
106 drawn so that it appears shifted 499 screen image pixels left, it
107 needs to be drawn from the 499/12.345=40.42122th image pixel. Is
108 might seem that indeed it would be enough to ask the system to
109 begin drawing from image pixel 40, and offset int(0.42122*12.345)=5
110 screen pixels to the left, however, that procedure will not account
111 for the correct fixed point roundoff that accumulates as system
112 scales the image. For zoom factor 12.345 this roundoff sequence is,
113 as we seen before, (12,25,37,49,62,74,86,99,111,123) for the first
114 10 pixels displayed, that occupy (12,13,12,12,13,12,12,13,12,12)
115 screen pixels correspondingly. For the pixels starting at 499, the
116 sequence is (506,519,531,543,556,568,580,593,605,617) offsets or
117 (13,12,12,13,13,12,12,13,12,12) widths -- note the two subsequent
118 13s there. This sequence begins to repeat itself after 200
119 iterations (12.345*200=2469.000), which means that in order to
120 achieve correct display results, the image must be asked to be
121 displayed from as far as image pixel 0 if image's first pixel on
122 the screen is between 0 and 199 ( or for screen pixels 0-2468),
123 then from image pixel 200 for offsets 200-399, ( screen pixels
124 2469-4937), and so on.
125 Since the system internally allocates memory for image scaling,
127 that means that up to
128 2*200*min(window_width,image_width)*bytes_per_pixel unneccessary
129 bytes will be allocated for each image drawing call (2 because the
130 calculations are valid for both the vertical and horizontal
131 strips), and this can lead to slowdown or even request failure when
132 image or window dimensions are large. The proposed solution is to
133 roundoff accepted zoom factors, so these offsets are kept small -
134 for example, N.25 zoom factors require only max 1/.25=4 extra
135 pixels. When "zoomPrecision" value is 100, zoom factors are rounded
136 to 0.X2, 0.X4, 0.X5, 0.X6, 0.X8, 0.X0, thus requiring max 50 extra
137 pixels.
138 NB. If, despite the efforts, the property gets in the way, increase
140 it to 1000 or even 10000, but note that this may lead to problems.
141 Default value: 100
143 Methods
145 on_paint SELF, CANVAS
146 The "Paint" notification handler is mentioned here for the specific
147 case of its return value, that is the return value of internal
148 "put_image" call. For those who might be interested in "put_image"
149 failures, that mostly occur when trying to draw an image that is
150 too big, the following code might be useful:
151 sub on_paint
153 {
154 my ( $self, $canvas) = @_;
155 warn "put_image() error:$@" unless $self-> SUPER::on_paint($canvas);
156 }
157 screen2point X, Y, [ X, Y, ... ]
159 Performs translation of integer pairs integers as (X,Y)-points from
160 widget coordinates to pixel offset in image coordinates. Takes in
161 account zoom level, image alignments, and offsets. Returns array of
162 same length as the input.
163 Useful for determining correspondence, for example, of a mouse
165 event to a image point.
166 The reverse function is "point2screen".
168 point2screen X, Y, [ X, Y, ... ]
170 Performs translation of integer pairs as (X,Y)-points from image
171 pixel offset to widget image coordinates. Takes in account zoom
172 level, image alignments, and offsets. Returns array of same length
173 as the input.
174 Useful for determining a screen location of an image point.
176 The reverse function is "screen2point".
178 watch_load_progress IMAGE
180 When called, image viewer watches as IMAGE is being loaded ( see
181 "load" in Prima::Image ) and displays the progress. As soon as
182 IMAGE begins to load, it replaces the existing "image" property.
183 Example:
184 $i = Prima::Image-> new;
186 $viewer-> watch_load_progress( $i);
187 $i-> load('huge.jpg');
188 $viewer-> unwatch_load_progress;
189 Similar functionality is present in Prima::Dialog::ImageDialog.
191 unwatch_load_progress CLEAR_IMAGE=1
193 Stops monitoring of image loading progress. If CLEAR_IMAGE is 0,
194 the leftovers of the incremental loading stay intact in "image"
195 propery. Otherwise, "image" is set to "undef".
196 zoom_round ZOOM
198 Rounds the zoom factor to "zoomPrecision" precision, returns the
199 rounded zoom value. The algorithm is the same as used internally in
200 "zoom" property.
201
203 Dmitry Karasik, <dmitry@karasik.eu.org>.
204
206 Prima, Prima::Image, Prima::ScrollWidget, Prima::Dialog::ImageDialog,
207 examples/iv.pl.
208perl v5.36.0 2022-07-22 Prima::ImageViewer(3)