POMOC WINAMPA

WAVEFORM

BRIGHTNESS **

VIDEO ECHO effect **

When you hit 'm' to show the preset-editing menu, several items show up. If you explore the sub-menus, you'll see that all of the properties that make up the preset you're currently viewing are there. The values you can specify here (such as zoom amount, rotation amount, wave color, etc.) are all static values, meaning that they don't change in time. For example, take the 'zoom amount' option under the 'motion' submenu. If this value is 1.0, there is no zoom. If the value is 1.01, the image zooms in 1% every frame. If the value is 1.10, the image zooms in 10% every frame. If the value is 0.9, the image zooms out 10% every frame; and so on.

However, presets get far more interesting if you can take these parameters (such as the zoom amount) and animate them (make them change over time). For example, if you could take the 'zoom amount' parameter and make it oscillate (vary) between 0.9 and 1.1 over time, the image would cyclically zoom in and out, in time.

You can do this-by writing 'per-frame' and 'per-vertex' equations. Let's start with 'per-frame' equations. These are executed once per frame. So, if you were to type the following equation in:

...then the zoom amount would oscillate between 0.9 and 1.1 over time. (Recall from your geometry classes that sin() returns a value between -1 and 1.) The equation says: "take the static value of 'zoom', then replace it with that value, plus some variation." This particular equation would oscillate (cycle) every 6.28 seconds, since the sin() function's period is 6.28 (PI*2) seconds. If you wanted it to make it cycle every 2 seconds, you could use:

Now, let's say you wanted to make the color of the waveform (sound wave) that gets plotted on the screen vary through time. The color is defined by three values, one for each of the main color components (red, green, and blue), each in the range 0 to 1 (0 is dark, 1 is full intensity). You could use something like this:

It's nice to stagger the frequencies (1.13, 1.23, and 1.33) of the sine functions for the red, green, and blue color components of the wave so that they cycle at different rates, to avoid them always being all the same (which would create a greyscale wave).

Here is a full list of the variables available for writing per-frame equations:

Some of the variables are read-only, meaning that you shouldn't change their values them through the equations. You can; it won't stop you; but the results are unpredictable.

You can also make up to 30 of your own variables. For example:

This would make the zoom amount increase when the music is loud, and decrease when the music is quiet.

HOWEVER, custom variables do not carry over from per-frame equations to per-vertex equations; if you set a custom variable's value in the per-frame equations, and try to read it in the per-vertex equations, you will not get the correct value. Instead, you have to "bridge the gap" using 32 special variables: q1 through q32. This is usually only used when you want to precompute some custom values in the per-frame equations for later use in the per-vertex equations (or for use in the pixel shaders). For a good example of this, see the 'dynamic swirls' preset. See below for more information on q1-q32.

So far we've discussed only how to change parameters based on time. What if you wanted to also vary a parameter, such as the zoom amount, in different ways, for different locations on the screen? For example, normally, the result of the 'zoom' parameter is to just do a flat zoom. This doesn't look very realistic, because you don't see any perspective in the zoom. It would be better if we could give a unique zoom amount to each pixel on the screen; we could make the pixels far away from the center zoom more, and this would give it more perspective. In order to do this, we use "per-vertex" equations, instead of per-frame equations.

The code for this per-vertex equation is simple:

Where 'rad' is the radius of the pixel if it were cast into polar coordinates; from another perspective, 'rad' is the distance of the pixel from the center of the screen. 'rad is zero at the center, and 1 at the corners. So if we run the above code, the image will be zoomed into 10% more at the edges of the screen than at the center.

The per-vertex equations are really just like the per-frame equations, except for a variables. The following variables are available exclusively to per-vertex equations (and not to per-frame equations):

The main reason for distinction between per-frame and per-vertex equations is simple: SPEED. If you have a per-vertex equation that doesn't make use of the x, y, rad, or ang variables, then there's no reason for it to be executed per-vertex; it could be executed once per frame, and the result would be the same. So, here's a maxim to write on the wall:

"If a per-vertex equation doesn't use at least one of the variables { x, y, rad, ang }, then it should be actually be a per-frame equation."

You might be wondering how on earth all these formulas could be computed for every pixel on the screen, every frame, and still yield a high frame rate. Well, that's the magic of the hamster. And the fact that it really does the processing only at certain points on the screen, then interpolates the results across the space between the points. In the config panel, the "mesh size" option defines how many points (in X and Y) there are at which the per-vertex equations are actually computed. When you crank this option up, you start eating up CPU cycles rather quickly.

Declaring and using your own variables is easy-in some bit of code (init equations, per-frame equations, etc.) you just write something like the following:

This creates a variable called 'billy' and sets its value to 5.3. You can then freely read and/or modify the value of 'billy' within that section of code.

However, sometimes it is desireable to create (really, initialize) a variable in an "init" equations, then use and/or update it in the "per-frame" equations. You can always do this, because paired init and per-frame equations share the same variable pool. In addition, the values of user-defined variables will persist from frame to frame.

There are three variable "pools" in MilkDrop:

So, you can probably guess that if you declare a variable in the preset init code, you can then read it in the preset per-frame code. You can also write to it (update it), and its value will persist to the next frame. All three pools work this way.

As explained, though, you can't read the value of 'billy' in when in another variable pool. (This is intentional, and keeps MilkDrop running nice and fast.) If you want to pass values around between variable pools, you need to use a set of special variables: q1, q2, q3, etc. on up to q32. See the next section for details on how they work and how to properly use them. Just remember: the Q variables (and later, the T variables) are the only ones that you can use to "jump" between (carry values between) variable pools.

You might notice that there are two other types of equations that weren't listed above. They are:

For these two code sections, persistent values don't really make sense, because there is no way to properly initialize them. Any user-defined variables in these code sections should just be treated as scratch variables, not persisting from frame to frame, from vertex to vertex, or from point to point (even though technically, they will... but it probably won't be what you want). The only thing that really makes sense here is when you want to carry values along from point to point as you run the custom wave per-point code; to do this, use q1-q32. (See the next section for a more detailed explanation.)

As we've just seen, you can't normally pass values around between variable pools. However, there is one mechanism for bridging this gap: the 'Q' variables. They are named q1, q2, q3, and so on, through q32. Their main function is to bridge the gap between various variable pools.

In MilkDrop 1.03 and later, you can write code that is executed only once, when a preset is loaded (switched to). This 'preset initialization' code does two useful things:

See the flow chart below for a brief, and complete, glance at how the values of the Q variables flow throughout MilkDrop.

Let's walk through the flow of the chart.

If you write to the values of q1..q32 from the "preset init code", the values you write will become the new 'base values' to which q1..q32 are initialized at the start of each frame, for the per-frame code. So when you access (read) q1-q32 in the per-frame code, you'll get the values that were *initially* set-over and over, every frame. You can then modify them (or not) in the per-frame code, and the (possibly modified values) will then be readable by the per-vertex code-as well as by all pixel shader code, and others. However, any modified values will not persist to the next frame; they will be reset again, at the start of the next frame, to the values they had at the end of the preset init code.

In the per-vertex code, the q1-q32 values start (for the first vertex in any frame) as the values they had at the end of the per-frame code. If you modify q1-q32 in the per-vertex code, those modified values will carry over from vertex to vertex. (This isn't a very desireable effect; you should avoid writing to the Q variables from the per-vertex equations.) Next frame, they will be reset to whatever value they had at the end of the [next frame's execution of the] per-frame code. (It's all in the diagram... look at that, and you'll just get it.)

There is one trick here. You might notice that the custom wave/shape init boxes are missing from the diagram. That's because the q variables coming out of them don't go anywhere. The Q values that come into the per-frame wave/shape equations come from the preset per-frame equations, as you can see. But, just to humor you: in the wave/shape init code, the Q values coming in are the results from the preset init code. Any Q values you write to there (in the wave/shape init code) will be meaningless; although you can write to (initialize) your own custom variables, and read those in later, in the wave/shape per-frame equations! So, really, you can still route data that way, if you really want to.

Side note: when you edit the preset init code and apply it (by hitting CTRL+ENTER), the init code will re-execute immediately. However, when you edit the regular per-frame/per-vertex code and hit CTRL+ENTER, the preset init code will NOT be re-executed; the results of the last execution will persist. If you change per-frame/per-vertex code and want to re-execute the initialization code (i.e. to randomize it or reset the preset), you'll have to save the preset and then re-load it.

(Historical note: nothing here has changed since MilkDrop 1; these diagrams were just re-designed to be much simpler to read. Actually, there was a bug in the old diagrams that is now fixed: on frame 0, they showed the Q values going straight from the (frame 0!?) per-frame code, into the custom wave/shape init code. On frame 0, those Q values actually come straight from the preset init code. HOWEVER, they are virtually useless, as discussed above.)

As of MilkDrop 1.04, two new features are available: custom shapes, and custom waves. A preset can have up to 4 of each.

With custom shapes, you can draw an n-sided shape (with 3-100 sides) anywhere on the screen, at any angle and size, in any color, and at any opacity. You even have the option to map the previous frame's image onto the shape, which makes for some incredible possibilities (such as realtime hardware fractals-see the 'Geiss-Feedback' preset). You can also write per-frame code to control all of these things about the shape(s). This way, they can react tothe audio or change over time-whatever you can imagine. You are limited tofour custom shapes per preset, however, each one of those can be instanced,which lets you draw a huge number (up to 1024) of them each frame, if you want to, and each one can be totally different (as long as the value ofthe 'instance' variable ends up influencing the other properties).

With custom waves, you can draw the waveform (or the frequency spectrum) wherever, whenever, and however you want; a great addition since MilkDrop 1.03, where only the built-in waveforms were possible. With custom waves you can also write per-frame code to control the waves, and per-point code to place every point (or line segment) on the wave exactly where you want, and in exactly the color you want, and so on.

Remember those q1-q32 variables that were committed at the end of the preset initialization code, then reset (to those values) at the beginning of each frame, and then (potentially) modified in the preset per-frame code? Those (potentially modified) values of q1-q32-as they were at the end of the preset's per-frame code, each frame-are piped into the custom wave &custom shape per-frame code. So if you read 'q3' in the custom wave per-frame code, what you're really reading is the value of 'q3' as it was left at the end of this frame's per-frame code. Again, see the q_vars.png image for a diagram of the flow of the values of the q1-q32 varibles.

For custom waves and shapes, you can modify q1-q32, if you like, in the per-frame equations. As usual, the values of the Q variables will not persist from frame to frame, though-they are reset on each new frame, to match the values they had at the end of the *preset's* per-frame code, this frame.

For custom waves, you also have one more link in the chain: per-point (aka per-vertex) code. This code is executed once for each data point in the waveform. The initial values of q1-q32 coming in (for the first point) are the values that stood at the end of the custom wave per-frame code, this frame. If you then modify q1-q32 in the per-point code (or even if you don't), the values will pass on to the next point. You could, for example, smooth out a waveform using this.

THE 'T' VARIABLES

There are 8 additional variables available for custom waves and shapes: t1-t8. These are very similar to the Q variables, but they exist only for custom waves &shapes. To see how the data flows from variable pool to variable pool for the T vars, take a look at the diagram below. Like the Q variables, they exist to help you bridge some gaps between variable pools. However, the T variables are a bit simpler to understand than the Q's. The diagram below should explain it all.

The world of realtime computer graphics made a huge stride around 2002 - 2003, with the advent of pixel shaders. Lots of people want to learn how to use pixel shaders; writing presets for MilkDrop is a great way to learn them, because you get to see the effects of your code instantly, on the screen.

MilkDrop 1 ran on what is called the "fixed function" graphics pipeline. That meant that certain common graphics operations-and very few of them-could be executed for each pixel. You could do a few things-maybe multiply by a texture or a color, then maybe one more simple operation-but that was about it.

Newer presets (MilkDrop 2 and later) can take advantage of programmable pixel shaders. GPUs (graphics processing units) are now capable of executing dozens, even thousands (on more expensive hardware) of instructions per pixel. To tell the GPU what to do at each pixel, you write some code called a "pixel shader". It looks a lot like C, except you'll see the types float3 (...often representing a color, or maybe a 3D coordinate), as well as float2 and float4, as often as you'll see the simple "float" type. There is also a lot of emphasis on sampling from textures. Textures can either be procedural (like the image from the previous frame, or a nicely gaussian-blurred version of it, or a procedurally- generated noise texture), or they can be loaded from disk. To sample from a texture on disk (...but cached in video memory, of course), in the shader, you simply specify the name of the image file you want to load, and how you want to sample it (what kind of filtering & wrapping) as well as where (the UV coordinates, like XY coordinates, always in the [0..1] range). It reads the sample (as a float4-some image formats have four channels instead of just r/g/b). You can then do whatever you like (mathematically) with that sample, take other samples, combine them, and so on. The final output of the shader is always a color value, and it is this color value that is written to the render target (an internal texture, or the screen).

When designing presets, please adhere to the pixel shader 'quality assurance' guidelines in the above section, as they are very important. But, in order to make sure the presets you create work well on other systems, please also keep in mind:

One feature that preset authors should definitely be aware of is the variable monitoring feature, which lets you monitor (watch) the value of any per-frame variable you like. First, hit the 'N' key to show the monitor value, which will probably display zero. Then all you have to do is add a line like this to the per-frame equations:

where 'x' is the variable or expression you want to monitor. Once you hit CTRL+ENTER to accept the changes, you should see the value of the per-frame variable or expression in the upper-right corner of the screen!

Once again, note that it only works for *per-frame* equations, and NOT for per-vertex equations.

Following is a list of the functions supported by the expression evaluator (for preset init, per-frame, and per-vertex equations; NOT for pixel shaders). The list was blatently ripped from the help box of Justin Frankels' AVS plug-in, since MilkDrop uses the expression evaluator that he wrote.

Format your expressions using a semicolon (;) to delimit between statements. Use parenthesis ['(' and ')'] to denote precedence if you are unsure. The following operators are available:

The following functions are available: