Enlarging and reducing the screen
ZOOM
instruction: change size of part of screen
Zoom source number, x1 ,y1 ,x2,y2 To destination number,x3,y3,x4,y4
This one command allows you to produce a range of remarkable effects that change the size of the image in any rectangular area of the screen. Depending on the relative sizes of the source and destination areas, images can be magnified, shrunk, squashed and stretched as you wish. ZOOM is qualified by the number of the screen from where your source picture will be taken, followed by the coordinates of the top left-hand corner and bottom right-hand corner of the area to be grabbed, After the TO structure, give the, number of the destination screen and the new coordinates of the area which is to hold the zoomed image. AMOS Professional will automatically re-size the image.
The LOGIC function may be used to grab an image from the appropriate logical screen, instead of specifying a physical screen number. In the same way, you are allowed to deposit a zoomed image to a logical screen. This is explained below.
Physical and logical screens
When you watch the moving images shown at the cinema or on video, you are watching an
illusion. Graphical animation in the movies is created by a fast sequence of still pictures known
as frames. Television screens do not display moving images either. They fool the brain and the
eye by updating still images on the screen, fifty limes every second.
In order to create really smooth moving graphics, your computer has to complete all new drawing operations in less than one fiftieth of a second. So the AMOS Professional programmer must achieve this speed, otherwise programs will suffer from an ugly flicker. The problem is solved by using a technique that switches between screens during drawing operations. This is how it works.
Think of the actual area where images are displayed as the "physical" screen. Now imagine that there is a second screen which is completely invisible to the eye, where new drawing operations are executed. Call that the "logical" screen. Flicker-free movement is achieved by switching between the physical and logical screen.
The physical screen is displayed as usual, then once the new image has been drawn on the logical screen, they are swapped over. The old physical screen becomes the current logical screen, and is used to receive the drawing operations that will make up the next image. This process is completely automatic when using the DOUBLE BUFFER command, which is fully explained in Chapter 7.2.
SCREEN SWAP
instruction: swap over logical and, physical screens
Screen Swap
Screen Swap number