How to obtain individual button images from a larger (composite) image by specifying pixel coordinates.
NOTE First make sure that database is running on your localhost SilverStream Server
See the chapter on the Form Designer in the Tools Guide
Uploading an image for each button in your application may cost you in computational speed. To avoid having to upload multiple images for the various buttons images, you can upload a composite image of all the buttons, then use each button's image properties to access the only relevant portion of the image. This cropping technique is useful if you want to minimize the number of individual image files you maintain for your application.
The example uses a single image file as the source for multiple button images. The single large image is actually a composite of several images. You can extract individual portions of the large image by specifying the pixel coordinates for the upper left corner and the width and height.
When you run the form and click on a button in the central frame, the pixel coordinates for the button are displayed in the text box. For example if you click on the up image for the ADD button, the following is displayed: "Coordinates of ImageButton: x=1, y=1, w = 63, h = 26."
The following describes how to specify cropping values for the composite image so that a button displays a portion of the composite image.
buttons.JPG 1 30 63 26
This information specifies that:
The following code uses
setDownImage() to change the images assigned to an image button. The button has both Up and Down images. A second button lets the user switch between two pairs of images for the button. The images are in a single image file that is a composite of all the images.
This is a code fragment in the handle_listImages_valueChanged() method.
//Get the image. Image imgBig = getImage(agGeneral.getDatabaseURL() + "/SilverStream/Objectstore/Images/buttons.JPG"); //Get the section you're interested in. (UP Image) cropped= new FilteredImageSource (imgBig.getSource(), new CropImageFilter (xCoordinate, yCoordinate, width, height)); //Assign to the image variable. little = createImage (cropped); //Set the up image property of the image button. //ibDynamic is an AgcButtonImage object ibDynamic.setUpImage(little); //Get the section you're interested in. (DOWN Image) cropped = new FilteredImageSource (imgBig.getSource(), new CropImageFilter (xCoordinate, 30, width, height)); //Assign to the image variable. little = createImage (cropped); //Set the down image property of the image button. ibDynamic.setDownImage(little);
croppedholds the cropped image, which is created with
FilteredImageSourcetakes the big image and a filter object (in this case a
CropImageFilterobject) to produce image data for a filtered version of the big image.
ImageProducerthat created the large image.
CropImageFilterclass is used for cropping images. It identifies a rectangular region that can be applied to an image source. Its constructor takes the (x,y) location of the upper left corner of the new image, and its width and height.
createImage(), a method of Component, creates a new image object from the filter specifications.
setUpImage()sets the "up" button image (that is, the button in its unpressed state) to the extracted image.
cropped, this time to a different region on the big image. Note that the y-coordinate is set to 30 to define this region. The x-coordinate, the width and height values of the new image are the same.
setDownImage()sets the "down" button image (that is, the button in its pressed state) to the new extracted image.