35 lines
5.4 KiB
Plaintext
35 lines
5.4 KiB
Plaintext
Wellcome to Gem-graph !
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Gem-graph lets you move or transform drawn objects. You can draw anything you like. You can make it move or transform as you like. You can use it to make a game. You can use it to make an animated representation of a phenomenon that interests you (a model). You can represent what you want simply or in more realistic detail. Simple parts and more detailed parts can coexist in the same design. You can watch what you've created evolve without interfering or guiding it towards what you want to achieve. You can observe it in detail, go back, start again, measure, compare and keep the results that interest you so that you can play them again.
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All this comes at a price. A complicated model will require more work than a simpler one, but it is possible to start with something simple and develop it little by little. In any case, you must draw what you want to see and say how you want it to move. Gem-graph can't do that for you. Gem-graph can only help you to draw and say how you want your drawings to be transformed. It can give you powerful tools to do this. All this is possible because the drawings that gem-graph manipulates are made up of simple elements and the mechanisms that move them are also based on combinations of simple rules that can therefore be processed automatically. The tools provided by gem-graph give you the power of the automaton it uses to draw and animate your designs, and this manual is here to help you learn how to master them.
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One way of doing this is to reproduce a very simple example, such as when a word processing program asks you to write "Hello world". For gem-graph, the equivalent of "Hello world" will be to move a some small line on your screen. Once you've done this simple example, you'll know enough to quickly build and animate much more complex drawings that suit your desires. If you like learning this way, this example is explained (here). If you prefer to learn by reading what the commands you see on the screen do, they have been detailed (here). The table of contents goes from the simplest to the most complicated. How to set up a simple model, observe it and measure what it does, then transform it by changing what you see and how it reacts.
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Our "Hello world" is the simplest program that gem-graph can execute. It consists of a single short arrow, which moves in a straight line in a single direction. To do this, we first had to draw this little arrow and then make it move. The result is certainly not very exciting, but this example is enough to show how a drawing is made and how it is animated. One state and one rule are enough. The rule only says: if an arrow is drawn here, I erase it and redraw it on the next square. For the moment, you don't need to know in detail how the rule works (it's described here). All that gem-graph needs to know is written in the "Hello world" file (here). If you open this file, you'll find a description of the arrow (here) and its movement (here).
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To improve this model, it is possible to give the arrow the ability to move in two directions: forwards or backwards. To do this, we need to add a second rule. This second rule says: if an arrow is drawn here, I erase it and redraw it on the previous square. A random draw (described here) is also necessary to determine whether the first or second rule applies. With these two rules and the random draw, the arrow now sometimes goes forwards, sometimes backwards. We can call this second model a "random walk".
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The second model (the random walk) had one state (the arrow) and two rules (forward/backward). Now here's a model with two states and two rules: the pendulum. This time, the arrow can be drawn either tilted forwards or tilted backwards (these are the two possible states) and the two rules switch the drawn arrow from one state to the other or vice versa. In the file, the states are (here) and the rules (here). The pendulum does not change place, but alternates between left and right. Like the previous ones, the programme is slowed down so that you can see the movements.
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Once you know how to write a state and a rule, you can write thousands of them: they will always be combinations of the same elementary form. However, it is also possible to combine programs: for example, you can combine the reports and rules from the two previous models to create a new model that shows both phenomena simultaneously. Once again, in the file, the states are (here) and the rules (here).
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A final simple example shows how a single rule can be applied to a multitude of states. The rule is the same as for the first model: an arrow can only be moved one square forward, but this time you have to check that the square forward is free. If it isn't, the arrow won't move. And this time, the space contains a multitude of arrows that have been randomly placed all over the place (see details here).
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When you open this model, you see a multitude of small lines, all similar, some vertical, some horizontal, placed on a grid. When you set the model in motion, you see these little lines moving from left to right if they are horizontal, and up and down if they are vertical (a second rule vas added to do that). Their number is constant. They don't change shape or direction. There seems to be no accident when they cross. Nothing else happens.
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These five examples give an initial idea of the diversity of possible models and the operations that can be performed on them.
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