Visual Basic.NET How to Program (PDF)

716 Graphics and Multimedia Chapter 16
Fig. 16.23 Image resizing (part 3 of 3).
Line 16 declares Image reference mImage. The Shared Image method From-
File then retrieves an image stored on disk and assigns it to mImage (line 27). Line 24
uses Form method CreateGraphics to create a Graphics object associated with the
Form; we use this object to draw on the Form. Method CreateGraphics is inherited
from class Control; all Windows controls, such as Buttons and Panels, also provide
this method. When users click Set, the width and height parameters are validated to ensure
that they are not too large. If the parameters are valid, line 46 calls Graphics method
Clear to paint the entire Form in the current background color. Line 49 calls Graphics
method DrawImage with the following parameters: the image to draw, the x-coordinate
of the upper-left corner, the y-coordinate of the upper-left corner, the width of the image
and the height of the image. If the width and height do not correspond to the image’s original
dimensions, the image is scaled to fit the new specifications.
16.11 Animating a Series of Images
The next example animates a series of images stored in an array. The application uses the
same techniques to load and display Images as those illustrated in Fig. 16.23. The images
were created with Adobe Photoshop.
The animation in Fig. 16.24 uses a PictureBox, which contains the images that we
animate. We use a Timer to cycle through the images, causing a new image to display
every 50 milliseconds. Variable count keeps track of the current image number and
increases by one every time we display a new image. The array includes 30 images (numbered
0–29); when the application reaches image 29, it returns to image 0. The 30 images
were prepared in advance with a graphics software package and placed in the images
folder inside the bin/Debug directory of the project.
Lines 19–22 load each of 30 images and place them in an ArrayList. ArrayList
method Add allows us to add objects to the ArrayList; we use this method in lines 20–
21 to add each Image. Line 25 places the first image in the PictureBox, using the