69 lines
2.9 KiB
Plaintext
69 lines
2.9 KiB
Plaintext
{ (define LIBNAME "Animated Images")
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(include "head.tinc") }
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<p>The teachpack provides two kinds of functions. The first four allow
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students to simulate a small world of animated drawings and games:
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<menu>
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<li><code>{(idx big-bang)} : Number Number Number World -> true</code><br>
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<code>(big-bang width height n w)</code>
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creates and shows a width x height canvas,
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starts the clock,
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makes it tick every n seconds,
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and makes w the first world
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<li><code>{(idx on-tick-event)} : (World -> World) -> true</code><br>
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<code>(on-tick-event tock)</code> means that DrScheme must call <code>tock</code>
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on the current world every time the clock ticks; it uses the result as the next world
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<li><code>{(idx on-key-event)} : (World KeyEvent -> World) -> true</code><br>
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<code>(on-key-event change)</code> means that DrScheme must call
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<code>change</code> on the current world and a (representation of the)
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keyevent for every keystroke the programmer (user of the computer) makes; it uses
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the result as the next world
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<pre>
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<code>
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;; A KeyEvent is one of:
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;; -- Char (char?)
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;; -- Symbol (symbol?)
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</code>
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When the Keyevent is a char, the programmer (user of the computer) has hit an
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alphanumeric key. Symbols such as <code>'left</code>, <code>'right</code>,
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<code>'up</code>, <code>'down</code>, <code>'release</code> denote arrow keys
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or the events of releasing a key on the keypad.
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</pre>
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<li><code>{(idx on-redraw)} : (World -> Image) -> true</code><br>
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<code>(on-tick-event world->image)</code> means that DrScheme
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calls <code>world->image</code> whenever the canvas must be redrawn; the
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result is displayed in the teachpack's canvas
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<li><code>{(idx end-of-time)} : String u Symbol -> World</code><br> When DrScheme
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evaluates <code>(end-of-time)</code>, it stops the clock and displays the
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given string or symbol; no further tick events, key events, or redraw events
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take place until the world is created again. </menu></p>
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<p>The rest are functions for creating scenes:
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<menu>
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<li><code>{(idx nw:rectangle)} : Number Number Mode Color -> Image</code><br>
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<code>(nw:rectangle width height mode color)</code>
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creates a width x height rectangle, solid or outlined,
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with its anchor in the NW corner
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<li><code>{(idx empty-scene)} : Number Number -> Scene</code><br>
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<code>(empty-scene width height)</code>
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creates a width x height "scene" (frame with origin in NW)
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<li><code>{(idx place-image)} : Image Number Number Scence -> Scene</code><br>
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<code>(place-image image x y scene)</code>
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places image at (x,y) into scene; (x,y) are comp. graph. coordinates
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<li><code>{(idx run-movie)} : (Listof Image) -> true </code><br>
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<code>(run-movie loi)</code>
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shows the list of images in loi, time-delayed
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</menu></p>
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<p>Finally, the teachpack provides all the functions that image.ss provides. </p>
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{(include "foot.tinc")}
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