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::Widget::ScrollWidget"
21 and inherits its document scrolling behavior and programming interface.
22 See Prima::Widget::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 scaling ist::XX
51 Applies scaling when drawing an image.
52 Default: "ist::Box", default cheap scaling.
54 Warning: scaling types above the "ist::Box" might be somewhat
56 expensive
57 stretch BOOLEAN
59 If set, the image is simply stretched over the visual area, without
60 keeping the aspect. Scroll bars, zooming and keyboard navigation
61 become disabled.
62 quality BOOLEAN
64 A boolean flag, selecting if the palette of "image" is to be copied
65 into the widget palette, providing higher visual quality on
66 paletted displays. See also "palette" in Prima::Widget.
67 Default value: 1
69 valignment INTEGER
71 One of the following "ta::XXX" constants:
72 ta::Top
74 ta::Middle or ta::Center
75 ta::Bottom
76 Selects the vertical image alignment.
78 NB: "ta::Middle" value is not equal to "ta::Center"'s, however the
80 both constants produce equal effect here.
81 Default value: "ta::Bottom"
83 zoom FLOAT
85 Selects zoom level for image display. The acceptable value range is
86 between 0.01 and 100. The zoom value is rounded to the closest
87 value divisible by 1/"zoomPrecision". For example, is
88 "zoomPrecision" is 100, the zoom values will be rounded to the
89 precision of hundredth - to fiftieth and twentieth fractional
90 values - .02, .04, .05, .06, .08, and 0.1 . When "zoomPrecision" is
91 1000, the precision is one thousandth, and so on.
92 Default value: 1
94 zoomPrecision INTEGER
96 Zoom precision of "zoom" property. Minimal acceptable value is 10,
97 where zoom will be rounded to 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0 .
98 The reason behind this arithmetics is that when an image of an
100 arbitrary zoom factor is requested to be displayed, the image
101 sometimes must be drawn from a fraction image pixel - for example,
102 10x zoomed image shifted 3 pixels left, must be displayed so the
103 first image pixel from the left occupies 7 screen pixels, and the
104 next ones - 10 screen pixels. That means, that the correct image
105 display routine must ask the system to draw the image at offset -3
106 screen pixels, where the first image pixel column would correspond
107 to that offset.
108 When the zoom factor is fractional, the picture is getting more
110 complex. For example, with zoom factor 12.345, and zero screen
111 offset, the first image pixel begins at the 12th screen pixel, the
112 next one - at the 25th ( because of the roundoff ), then the 37th
113 etc etc. If the image is 2000x2000 pixels wide, and is asked to be
114 drawn so that it appears shifted 499 screen image pixels left, it
115 needs to be drawn from the 499/12.345=40.42122th image pixel. Is
116 might seem that indeed it would be enough to ask the system to
117 begin drawing from image pixel 40, and offset int(0.42122*12.345)=5
118 screen pixels to the left, however, that procedure will not account
119 for the correct fixed point roundoff that accumulates as system
120 scales the image. For zoom factor 12.345 this roundoff sequence is,
121 as we seen before, (12,25,37,49,62,74,86,99,111,123) for the first
122 10 pixels displayed, that occupy (12,13,12,12,13,12,12,13,12,12)
123 screen pixels correspondingly. For the pixels starting at 499, the
124 sequence is (506,519,531,543,556,568,580,593,605,617) offsets or
125 (13,12,12,13,13,12,12,13,12,12) widths -- note the two subsequent
126 13s there. This sequence begins to repeat itself after 200
127 iterations (12.345*200=2469.000), which means that in order to
128 achieve correct display results, the image must be asked to be
129 displayed from as far as image pixel 0 if image's first pixel on
130 the screen is between 0 and 199 ( or for screen pixels 0-2468),
131 then from image pixel 200 for offsets 200-399, ( screen pixels
132 2469-4937), and so on.
133 Since the system internally allocates memory for image scaling,
135 that means that up to
136 2*200*min(window_width,image_width)*bytes_per_pixel unneccessary
137 bytes will be allocated for each image drawing call (2 because the
138 calculations are valid for both the vertical and horizontal
139 strips), and this can lead to slowdown or even request failure when
140 image or window dimensions are large. The proposed solution is to
141 roundoff accepted zoom factors, so these offsets are kept small -
142 for example, N.25 zoom factors require only max 1/.25=4 extra
143 pixels. When "zoomPrecision" value is 100, zoom factors are rounded
144 to 0.X2, 0.X4, 0.X5, 0.X6, 0.X8, 0.X0, thus requiring max 50 extra
145 pixels.
146 NB. If, despite the efforts, the property gets in the way, increase
148 it to 1000 or even 10000, but note that this may lead to problems.
149 Default value: 100
151 Methods
153 on_paint SELF, CANVAS
154 The "Paint" notification handler is mentioned here for the specific
155 case of its return value, that is the return value of internal
156 "put_image" call. For those who might be interested in "put_image"
157 failures, that mostly occur when trying to draw an image that is
158 too big, the following code might be useful:
159 sub on_paint
161 {
162 my ( $self, $canvas) = @_;
163 warn "put_image() error:$@" unless $self-> SUPER::on_paint($canvas);
164 }
165 screen2point X, Y, [ X, Y, ... ]
167 Performs translation of integer pairs integers as (X,Y)-points from
168 widget coordinates to pixel offset in image coordinates. Takes in
169 account zoom level, image alignments, and offsets. Returns array of
170 same length as the input.
171 Useful for determining correspondence, for example, of a mouse
173 event to a image point.
174 The reverse function is "point2screen".
176 point2screen X, Y, [ X, Y, ... ]
178 Performs translation of integer pairs as (X,Y)-points from image
179 pixel offset to widget image coordinates. Takes in account zoom
180 level, image alignments, and offsets. Returns array of same length
181 as the input.
182 Useful for determining a screen location of an image point.
184 The reverse function is "screen2point".
186 watch_load_progress IMAGE
188 When called, image viewer watches as IMAGE is being loaded ( see
189 "load" in Prima::Image ) and displays the progress. As soon as
190 IMAGE begins to load, it replaces the existing "image" property.
191 Example:
192 $i = Prima::Image-> new;
194 $viewer-> watch_load_progress( $i);
195 $i-> load('huge.jpg');
196 $viewer-> unwatch_load_progress;
197 Similar functionality is present in Prima::Dialog::ImageDialog.
199 unwatch_load_progress CLEAR_IMAGE=1
201 Stops monitoring of image loading progress. If CLEAR_IMAGE is 0,
202 the leftovers of the incremental loading stay intact in "image"
203 propery. Otherwise, "image" is set to "undef".
204 zoom_round ZOOM
206 Rounds the zoom factor to "zoomPrecision" precision, returns the
207 rounded zoom value. The algorithm is the same as used internally in
208 "zoom" property.
209
211 Dmitry Karasik, <dmitry@karasik.eu.org>.
212
214 Prima, Prima::Image, Prima::Widget::ScrollWidget,
215 Prima::Dialog::ImageDialog, examples/iv.pl.
216perl v5.38.0 2023-07-21 Prima::ImageViewer(3)