NAME¶
Prima::ImageViewer - standard image, icon, and bitmap viewer class.
DESCRIPTION¶
The module contains "Prima::ImageViewer" class, which provides image
displaying functionality, including different zoom levels.
"Prima::ImageViewer" is a descendant of
"Prima::ScrollWidget" and inherits its document scrolling behavior
and programming interface. See Prima::ScrollWidget for details.
API¶
Properties¶
- alignment INTEGER
- One of the following "ta::XXX" constants:
ta::Left
ta::Center
ta::Right
Selects the horizontal image alignment.
Default value: "ta::Left"
- image OBJECT
- Selects the image object to be displayed. OBJECT can be an
instance of "Prima::Image", "Prima::Icon", or
"Prima::DeviceBitmap" class.
- imageFile FILE
- Set the image FILE to be loaded and displayed. Is rarely
used since does not return a loading success flag.
- quality BOOLEAN
- A boolean flag, selecting if the palette of
"image" is to be copied into the widget palette, providing
higher visual quality on paletted displays. See also "palette"
in Prima::Widget.
Default value: 1
- valignment INTEGER
- One of the following "ta::XXX" constants:
ta::Top
ta::Middle or ta::Center
ta::Bottom
Selects the vertical image alignment.
NB: "ta::Middle" value is not equal to "ta::Center"'s,
however the both constants produce equal effect here.
Default value: "ta::Bottom"
- zoom FLOAT
- Selects zoom level for image display. The acceptable value
range is between 0.01 and 100. The zoom value is rounded to the closest
value divisible by 1/"zoomPrecision". For example, is
"zoomPrecision" is 100, the zoom values will be rounded to the
precision of hundredth - to fiftieth and twentieth fractional values -
.02, .04, .05, .06, .08, and 0.1 . When "zoomPrecision" is 1000,
the precision is one thousandth, and so on.
Default value: 1
- zoomPrecision INTEGER
- Zoom precision of "zoom" property. Minimal
acceptable value is 10, where zoom will be rounded to 0.2, 0.4, 0.5, 0.6,
0.8 and 1.0 .
The reason behind this arithmetics is that when image of arbitrary zoom
factor is requested to be displayed, the image sometimes must begin to be
drawn from partial pixel - for example, 10x zoomed image shifted 3 pixels
left, must be displayed so the first image pixel from the left occupies 7
screen pixels, and the next ones - 10 screen pixels. That means, that the
correct image display routine must ask the system to draw the image at
offset -3 screen pixels, where the first pixel column would correspond to
that pixel.
When zoom factor is fractional, the picture is getting more complex. For
example, with zoom factor 12.345, and zero screen offset, first image
pixel begins at 12th screen pixel, the next - 25th ( because of the
roundoff ), then 37th etc etc. Also, for example the image is 2000x2000
pixels wide, and is asked to be drawn so that the image appears shifted
499 screen image pixels left, beginning to be drawn from ~
499/12.3456=40.42122 image pixel. Is might seem that indeed it would be
enough to ask system to begin drawing from image pixel 40, and offset
int(0.42122*12.345)=5 screen pixels to the left, however, that procedure
will not account for the correct fixed point roundoff that accumulates as
system scales the image. For zoom factor 12.345 this roundoff sequence is,
as we seen before, (12,25,37,49,62,74,86,99,111,123) for first 10 pixels
displayed, that occupy (12,13,12,12,13,12,12,13,12,12) screen pixels. For
pixels starting at 499, this sequence is
(506,519,531,543,556,568,580,593,605,617) offsets or
(13,12,12,13,13,12,12,13,12,12) widths -- note the two subsequent 13s
there. This sequence begins to repeat itself after 200 iterations
(12.345*200=2469.000), which means that in order to achieve correct
display results, the image must be asked to be displayed from image pixel
0 if image's first pixel on the screen is between 0 and 199 ( or for
screen pixels 0-2468), from image pixel 200 for offsets 200-399, ( screen
pixels 2469-4937), and so on.
Since system internally allocate memory for image scaling, that means that
up to 2*200*min(window_width,image_width)*bytes_per_pixel unneccessary
bytes will be allocated for each image drawing call (2 because the
calculations are valid for both the vertical and horizontal strips), and
this can lead to slowdown or even request failure when image or window
dimensions are large. The proposed solution is to roundoff accepted zoom
factors, so these offsets are kept small - for example, N.25 zoom factors
require only max 1/.25=4 extra pixels. When "zoomPrecision"
value is 100, zoom factors are rounded to 0.X2, 0.X4, 0.X5, 0.X6, 0.X8,
0.X0, thus requiring max 50 extra pixels.
NB. If, despite the efforts, the property gets in the way, increase it to
1000 or even 10000, but note that this may lead to problems.
Default value: 100
Methods¶
- on_paint SELF, CANVAS
- The "Paint" notification handler is mentioned
here for the specific case of its return value, that is the return value
of internal "put_image" call. For those who might be interested
in "put_image" failures, that mostly occur when trying to draw
an image that is too big, the following code might be useful:
sub on_paint
{
my ( $self, $canvas) = @_;
warn "put_image() error:$@" unless $self-> SUPER::on_paint($canvas);
}
- screen2point X, Y, [ X, Y, ... ]
- Performs translation of integer pairs integers as
(X,Y)-points from widget coordinates to pixel offset in image coordinates.
Takes in account zoom level, image alignments, and offsets. Returns array
of same length as the input.
Useful for determining correspondence, for example, of a mouse event to a
image point.
The reverse function is "point2screen".
- point2screen X, Y, [ X, Y, ... ]
- Performs translation of integer pairs as (X,Y)-points from
image pixel offset to widget image coordinates. Takes in account zoom
level, image alignments, and offsets. Returns array of same length as the
input.
Useful for determining a screen location of an image point.
The reverse function is "screen2point".
- watch_load_progress IMAGE
- When called, image viewer watches as IMAGE is being loaded
( see "load" in Prima::Image ) and displays the progress. As
soon as IMAGE begins to load, it replaces the existing "image"
property. Example:
$i = Prima::Image-> new;
$viewer-> watch_load_progress( $i);
$i-> load('huge.jpg');
$viewer-> unwatch_load_progress;
Similar functionality is present in Prima::ImageDialog.
- unwatch_load_progress CLEAR_IMAGE=1
- Stops monitoring of image loading progress. If CLEAR_IMAGE
is 0, the leftovers of the incremental loading stay intact in
"image" propery. Otherwise, "image" is set to
"undef".
- zoom_round ZOOM
- Rounds the zoom factor to "zoomPrecision"
precision, returns the rounded zoom value. The algorithm is the same as
used internally in "zoom" property.
AUTHOR¶
Dmitry Karasik, <dmitry@karasik.eu.org>.
SEE ALSO¶
Prima, Prima::Image, Prima::ScrollWidget, Prima::ImageDialog,
examples/iv.pl.