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140 lines
3.5 KiB
Markdown
140 lines
3.5 KiB
Markdown
# Retro Snow
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In this project, you will create a retro animation using terminal escape
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sequences, that mimics falling snow. This is, in fact, a trivial
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particle system. Sophisticated particle systems are a routine part of
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visual effects in television and film as well as crucial tools in
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scientific computing.
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## A Particle
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A single particle looks like this:
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```c++
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struct Particle {
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int32_t line;
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int32_t column;
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};
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```
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Thus, a particle is made up of two 32 bit integers side-by-side. The
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first provides the line of the particle, the second its column.
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## Screen Size
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A default terminal window measures 80 characters across and 24 lines
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down. The origin is (1, 1) located at the top left corner.
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## Cursor Movement
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Snow flakes (particles) will be positioned using an old school VT100
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escape sequence. This sequence is:
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```text
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ESC [ line ; column H
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```
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with no spaces.
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Using `printf()`, a template string can be employed:
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```text
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"\033[%d;%dH"
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```
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In C++, you'd do something like this:
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```c++
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cout << "\033[" << line << ";" << column << "H";
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```
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Note that there are no new lines being printed since this would in
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itself move the cursor to the left edge of the next line and could
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even cause scrolling - a disaster in this project.
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## Erasing the Screen
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To erase the screen, use this escape sequence after first having moved
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to screen position (1, 1):
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```text
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"\033[2J"
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```
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## A C++ Object To Use As A Model
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The following C++ can be used to start your thinking about how to go
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about writing this project.
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```c++
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struct Particle {
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int32_t line;
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int32_t column;
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void Step();
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void Render();
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void Reset();
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};
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```
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### `Step()`
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All particles use the `Step()` function to move into the future. The
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`line` is increased by one and the `column` can either remain unchanged,
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move to the left or move to the right.
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If the particle's `line` exceeds 24, the particle is `Reset()`.
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### `Render()`
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To draw a particle, `Move()` to its location then print a "\*" all
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without emitting a new line. Before printing the "\*", check to ensure
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both the `line` and `column` are within the boundaries of the default
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terminal window (i.e. line between 1 and 24 and also column
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between 1 and 80).
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If the particle's position is outside this range, don't print anything.
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### `Reset()`
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A particle's initial `column` can be anywhere from 1 to 80 inclusive.
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Special care is given to setting the particle's initial `line`.
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Specifically, always place the particle above the visible screen...
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chosen randomly from -1 to -48. This allows for sufficient spacing so
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that the snow does not appear to fall in clumps.
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## The Storm
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A single snow flakes does not a blizzard make. Therefore, allocate a
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large number of them - perhaps 150 to 200 flakes. Since assembly
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language doesn't have actual C++ objects, each flake occupies only
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the 2 `int32_t` values. Suppose *n* is the number of flakes you choose
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to model. Then allocate *2 \* 4 \* n* bytes using `malloc()`. Since
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you will then `Reset()` every one of them, initializing the newly
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allocated memory is not needed.
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Then, you'll need a `StepAll()` and a `RenderAll()`.
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## The Main Loop
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* Position cursor at (1, 1).
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* Erase the screen.
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* `StepAll()`
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* `RenderAll()`
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* Position cursor at (1, 1) again and print a new line.
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* Delay a short time. In my implementation, I using `usleep()` to delay
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2<sup>17</sup> microseconds.
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Note only one new line is printed per frame - this is used to force all
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output to be flushed to the terminal.
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## Desired Outcome
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## Solution
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The solution is [here](./main.s).
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