Computer Science Canada

Need Some Explanation on View.Update
Author:  The 10 [ Sun Jan 22, 2006 12:56 pm ]
Post subject:  Need Some Explanation on View.Update
Hi, i need help understanding this program, its the smooth animation example from the turing examples.

code:
% The "SmoothAnimateHouse" program.

% This program demonstrates the View.Update and setscreen ("offscreenonly")

% Draw a house
drawbox (30, 30, 100, 100, black)
drawbox (50, 30, 80, 60, brightred)
drawbox (35, 70, 55, 90, green)
drawline (45, 70, 45, 90, green)
drawline (35, 80, 55, 80, green)
drawbox (75, 70, 95, 90, green)
drawline (85, 70, 85, 90, green)
drawline (75, 80, 95, 80, green)
drawline (30, 100, 65, 135, brightblue)
drawline (65, 135, 100, 100, brightblue)
drawline (90, 110, 90, 150, black)
drawline (75, 125, 75, 150, black)
drawline (75, 150, 90, 150, black)
locate (maxrow, 2)
put "Home sweet home" ..

% Create the picture
const PIC_WIDTH := 130
const PIC_HEIGHT := 160
var pic := Pic.New (0, 0, PIC_WIDTH, PIC_HEIGHT)

% Animate 10 of them around the screen
var x, y, dx, dy : array 1 .. 10 of int
cls
for i : 1 .. 10
    x (i) := Rand.Int (10, maxx - 10 - PIC_WIDTH)
    y (i) := Rand.Int (10, maxy - 10 - PIC_HEIGHT)
    dx (i) := Rand.Int (-3, 3)
    dy (i) := Rand.Int (-3, 3)
end for

loop
    cls
    locate (maxrow, 10)
    put "Old Animation Technique.  Press any key to see the new technique" ..
    for i : 1 .. 10
        if x (i) + dx (i) < 0 or x (i) + dx (i) + PIC_WIDTH > maxx then
            dx (i) := -dx (i)
        end if
        if y (i) + dy (i) < 0 or y (i) + dy (i) + PIC_HEIGHT > maxy then
            dy (i) := -dy (i)
        end if
        x (i) := x (i) + dx (i)
        y (i) := y (i) + dy (i)
        Pic.Draw (pic, x (i), y (i), picMerge)
    end for
    exit when hasch
end loop

% Read the character from the buffer.
var ch : string (1)
getch (ch)

% Now, any drawing to the screen won't appear until a View.Update is
% given.  Note that you can turn this off with
setscreen ("offscreenonly")
loop
    cls
    locate (maxrow, 10)
    put "New Animation Technique.  Press any key to quit" ..
    for i : 1 .. 10
        if x (i) + dx (i) < 0 or x (i) + dx (i) + PIC_WIDTH > maxx then
            dx (i) := -dx (i)
        end if
        if y (i) + dy (i) < 0 or y (i) + dy (i) + PIC_HEIGHT > maxy then
            dy (i) := -dy (i)
        end if
        x (i) := x (i) + dx (i)
        y (i) := y (i) + dy (i)
       
        % Note this only draws on the offscreen window.  Nothing appears
        % in the visible window.
        Pic.Draw (pic, x (i), y (i), picMerge)
    end for
    % All the houses have been drawn.  Now update the screen.
    View.Update
    exit when hasch
end loop
setscreen ("nooffscreenonly")


I dont understand what the array is doing in this program, whats the use of it?
I also dont understand how they made the animation?

Im trying to use this same tecnique in my final project so i would appreciate if someone could just explain this program for me.
Author:  Tony [ Sun Jan 22, 2006 1:34 pm ]
Post subject: 
the array just holds random locations

otherwise the example is quite well commented

you don't need to consern yourself with details of how animation is made, the important points are that the screen is set to
code:

View.Set("offscreenonly")


and that after you're done drawing your entire frame you update the buffer
code:

View.Update


so your program would look like
code:

View.Set("offscreenonly")
loop
   Draw
   Draw
   Draw
   View.Update
   cls
end loop
Author:  The 10 [ Sun Jan 22, 2006 2:46 pm ]
Post subject: 
Tony wrote:
the array just holds random locations


Thx for the reply Tony, but i still dont understand why you need the array there? I know it sounds like silly question, but i really wanna know.

Also i understand this is the way animation should be done.
Quote:

code:

View.Set("offscreenonly")
loop
   Draw
   Draw
   Draw
   View.Update
   cls
end loop


but i want to make the animation similar to the house one, so that's why i'd like to understand what happens in this part.
code:

loop
    cls
    locate (maxrow, 10)
    put "New Animation Technique.  Press any key to quit" ..
    for i : 1 .. 10
        if x (i) + dx (i) < 0 or x (i) + dx (i) + PIC_WIDTH > maxx then
            dx (i) := -dx (i)
        end if
        if y (i) + dy (i) < 0 or y (i) + dy (i) + PIC_HEIGHT > maxy then
            dy (i) := -dy (i)
        end if
        x (i) := x (i) + dx (i)
        y (i) := y (i) + dy (i)
       
        % Note this only draws on the offscreen window.  Nothing appears
        % in the visible window.
        Pic.Draw (pic, x (i), y (i), picMerge)
    end for
    % All the houses have been drawn.  Now update the screen.
    View.Update
    exit when hasch
end loop


so if someone could explain this to me? Crying or Very sad
Author:  Rasta Fella [ Sun Jan 22, 2006 4:45 pm ]
Post subject: 
Note the only difference between both techniques is that the later one has View.Update stuck into the loop. That's what makes the transition of all the "houses" smooth. As for learning Arrays...

Or for further explanation on "flexible arrays" and more check the Turing Walkthrough.
Author:  The 10 [ Sun Jan 22, 2006 6:09 pm ]
Post subject: 
Ok i understand now that the array is there to hold different values in 1 variable name.

Now i want to understand what's going on in this part of the program - the animation

code:

for i : 1 .. 10
        if x (i) + dx (i) < 0 or x (i) + dx (i) + PIC_WIDTH > maxx then
            dx (i) := -dx (i)
        end if
        if y (i) + dy (i) < 0 or y (i) + dy (i) + PIC_HEIGHT > maxy then
            dy (i) := -dy (i)
        end if
        x (i) := x (i) + dx (i)
        y (i) := y (i) + dy (i)
       
        % Note this only draws on the offscreen window.  Nothing appears
        % in the visible window.
        Pic.Draw (pic, x (i), y (i), picMerge)
    end for


I want to understand what's going on, as i dont understand how the houses move the way they do, and how they bounce of the edge.

:


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