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Some additional techniques for programming
graphics and animation, along with some new programming language
concepts. This material is optional
– you don’t need it to complete Project 2, or for the exams. |
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Techniques for : |
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Drawing geometric figures |
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Objects that follow the mouse |
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Animation |
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Small ideas: |
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Using trigonometry in programming graphical
layout |
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Named constants |
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for loops (another construct for iteration) |
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Mouse move events & dragging |
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Double buffering |
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Big idea: |
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Object-oriented programming |
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You can download the sample code for today from
the “Example Code” link on the CSE/IMT 100 web page. All the code is in a zip file;
ProjectSquiral is also available separately. |
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Sample files: |
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ProjectSquiral – interactive squirals |
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ProjectBlackSquiral – nicer colors, full screen |
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ProjectDrag – dragging an object |
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ProjectAnimate – very simple animation |
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ProjectAnimatedSquiral |
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ProjectBufferedSqural – illustrates double
buffering |
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In programming we often need to use various
constants, e.g. RGB combinations, the number of steps to take in a squiral,
etc. |
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It is good programming practice to give names to
these, rather than embedding the constants in your code. |
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Advantages: |
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Putting them at the beginning of your code makes
it easier to find and change them. |
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If you use the constant in several places and
want to change it, there’s just one place to change. |
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VB has various constants already built in. Examples: |
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vbRed, vbBlack, vbBlue, etc: colors |
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vbLeftButton: code for left mouse button pushed
(an integer) |
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Declaring your own: |
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Recall that VB, like most other modern
environments for building graphical user interfaces, uses an event model. |
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For example, we generate an event (and call an
appropriate procedure) whenever the user clicks on a button. |
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Whenever the mouse moves, VB generates a “mouse
move event” |
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You can do simple animations using the timer
control. On each call to the Timer
procedure, erase the form and draw the new figure. |
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If you are doing a complex animation, it will
take VB a bit of time to do the drawing. |
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Problem: flicker |
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Solution: double buffering |
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Draw the figure in a different picture that is
not visible |
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Copy the result into the visible picture |
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Notes