1Prima::ImageViewer(3) User Contributed Perl DocumentationPrima::ImageViewer(3)
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NAME

6       Prima::ImageViewer - standard image, icon, and bitmap viewer class.
7
8   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

DESCRIPTION

17       The module contains "Prima::ImageViewer" class, which provides image
18       displaying functionality, including different zoom levels.
19
20       "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

API

25   Properties
26       alignment INTEGER
27           One of the following "ta::XXX" constants:
28
29                   ta::Left
30                   ta::Center
31                   ta::Right
32
33           Selects the horizontal image alignment.
34
35           Default value: "ta::Left"
36
37       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
42       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
46       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
50       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
55       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
60           Default value: 1
61
62       valignment INTEGER
63           One of the following "ta::XXX" constants:
64
65                   ta::Top
66                   ta::Middle or ta::Center
67                   ta::Bottom
68
69           Selects the vertical image alignment.
70
71           NB: "ta::Middle" value is not equal to "ta::Center"'s, however the
72           both constants produce equal effect here.
73
74           Default value: "ta::Bottom"
75
76       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
85           Default value: 1
86
87       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
91           The reason behind this arithmetics is that when image of arbitrary
92           zoom factor is requested to be displayed, the image sometimes must
93           begin to be drawn from partial pixel - for example, 10x zoomed
94           image shifted 3 pixels left, must be displayed so the first image
95           pixel from the left occupies 7 screen pixels, and the next ones -
96           10 screen pixels.  That means, that the correct image display
97           routine must ask the system to draw the image at offset -3 screen
98           pixels, where the first pixel column would correspond to that
99           pixel.
100
101           When zoom factor is fractional, the picture is getting more
102           complex. For example, with zoom factor 12.345, and zero screen
103           offset, first image pixel begins at 12th screen pixel, the next -
104           25th ( because of the roundoff ), then 37th etc etc. Also, for
105           example the image is 2000x2000 pixels wide, and is asked to be
106           drawn so that the image appears shifted 499 screen image pixels
107           left, beginning to be drawn from ~ 499/12.3456=40.42122 image
108           pixel. Is might seem that indeed it would be enough to ask system
109           to begin drawing from image pixel 40, and offset
110           int(0.42122*12.345)=5 screen pixels to the left, however, that
111           procedure will not account for the correct fixed point roundoff
112           that accumulates as system scales the image. For zoom factor 12.345
113           this roundoff sequence is, as we seen before,
114           (12,25,37,49,62,74,86,99,111,123) for first 10 pixels displayed,
115           that occupy (12,13,12,12,13,12,12,13,12,12) screen pixels.  For
116           pixels starting at 499, this sequence is
117           (506,519,531,543,556,568,580,593,605,617) offsets or
118           (13,12,12,13,13,12,12,13,12,12) widths -- note the two subsequent
119           13s there.  This sequence begins to repeat itself after 200
120           iterations (12.345*200=2469.000), which means that in order to
121           achieve correct display results, the image must be asked to be
122           displayed from image pixel 0 if image's first pixel on the screen
123           is between 0 and 199 ( or for screen pixels 0-2468), from image
124           pixel 200 for offsets 200-399, ( screen pixels 2469-4937), and so
125           on.
126
127           Since system internally allocate memory for image scaling, that
128           means that up to
129           2*200*min(window_width,image_width)*bytes_per_pixel unneccessary
130           bytes will be allocated for each image drawing call (2 because the
131           calculations are valid for both the vertical and horizontal
132           strips), and this can lead to slowdown or even request failure when
133           image or window dimensions are large. The proposed solution is to
134           roundoff accepted zoom factors, so these offsets are kept small -
135           for example, N.25 zoom factors require only max 1/.25=4 extra
136           pixels. When "zoomPrecision" value is 100, zoom factors are rounded
137           to 0.X2, 0.X4, 0.X5, 0.X6, 0.X8, 0.X0, thus requiring max 50 extra
138           pixels.
139
140           NB. If, despite the efforts, the property gets in the way, increase
141           it to 1000 or even 10000, but note that this may lead to problems.
142
143           Default value: 100
144
145   Methods
146       on_paint SELF, CANVAS
147           The "Paint" notification handler is mentioned here for the specific
148           case of its return value, that is the return value of internal
149           "put_image" call.  For those who might be interested in "put_image"
150           failures, that mostly occur when trying to draw an image that is
151           too big, the following code might be useful:
152
153               sub on_paint
154               {
155                   my ( $self, $canvas) = @_;
156                   warn "put_image() error:$@" unless $self-> SUPER::on_paint($canvas);
157               }
158
159       screen2point X, Y, [ X, Y, ... ]
160           Performs translation of integer pairs integers as (X,Y)-points from
161           widget coordinates to pixel offset in image coordinates. Takes in
162           account zoom level, image alignments, and offsets. Returns array of
163           same length as the input.
164
165           Useful for determining correspondence, for example, of a mouse
166           event to a image point.
167
168           The reverse function is "point2screen".
169
170       point2screen   X, Y, [ X, Y, ... ]
171           Performs translation of integer pairs as (X,Y)-points from image
172           pixel offset to widget image coordinates. Takes in account zoom
173           level, image alignments, and offsets. Returns array of same length
174           as the input.
175
176           Useful for determining a screen location of an image point.
177
178           The reverse function is "screen2point".
179
180       watch_load_progress IMAGE
181           When called, image viewer watches as IMAGE is being loaded ( see
182           "load" in Prima::Image ) and displays the progress. As soon as
183           IMAGE begins to load, it replaces the existing "image" property.
184           Example:
185
186               $i = Prima::Image-> new;
187               $viewer-> watch_load_progress( $i);
188               $i-> load('huge.jpg');
189               $viewer-> unwatch_load_progress;
190
191           Similar functionality is present in Prima::ImageDialog.
192
193       unwatch_load_progress CLEAR_IMAGE=1
194           Stops monitoring of image loading progress. If CLEAR_IMAGE is 0,
195           the leftovers of the incremental loading stay intact in "image"
196           propery. Otherwise, "image" is set to "undef".
197
198       zoom_round ZOOM
199           Rounds the zoom factor to "zoomPrecision" precision, returns the
200           rounded zoom value. The algorithm is the same as used internally in
201           "zoom" property.
202

AUTHOR

204       Dmitry Karasik, <dmitry@karasik.eu.org>.
205

SEE ALSO

207       Prima, Prima::Image, Prima::ScrollWidget, Prima::ImageDialog,
208       examples/iv.pl.
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212perl v5.30.0                      2019-08-21             Prima::ImageViewer(3)
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