PixAnvil Help

How PixAnvil Works

PixAnvil compiles your JavaScript simulation code when you hit "Reset". It loads the code from three tabs:

• Setup code runs once, when the simulation is run (at startup, or when you press the "Reset" button). It typically creates persistent simulation objects and adds them to the scene.
• Loop code runs at every animation frame, unless the simulation is paused. It typically moves simulation objects around.
• UI code runs before Loop at every animation frame, and runs at full speed, even if the simulation is slowed down or paused. This allows you to move around and inspect a paused simulation.

The 3D vector class vec3 is key to most 3D work. In PixAnvil, this class is a renamed version of BABYLON.Vector3. By convention, vectors in PixAnvil are written with capital letters. Given two vectors A and B:

• var A=new vec3(x,y,z); creates a new vec3 with the given components.
• A.set(x,y,z); sets the vector's components to these values. This is sometimes needed when another object has a reference to the vector, such as an object position.
• var C=A.p(B); adds the two vectors, returning a new third vector, like + (plus).
• A.pe(B); adds B into A, changing A, like += (plus-equals).
• var C=A.m(B); subtracts the two vectors, returning a new third vector, like - (minus).
• A.me(B); adds B into A, changing A, like -= (minus-equals).
• var C=A.t(2.0); scales the A vector by the scalar, returning a new third vector, like * (times).
• A.te(2.0); scales the A vector, changing it, like *= (times-equals).
• A.rand(x,y,z); sets the vector's components to lie in the range [-x/2,+x/2], [-y/2,+y/2], [-z/2,+z/2].
• A.randSphere(diameter); makes a random 3-vector inside a sphere of this diameter (vector length can be as big as diameter/2)
• var c=length(A); makes the scalar c the length of the vector A.
• var C=normalize(A); makes C a unit-length vector pointing the same direction as the vector A. If the vector A is zero, the normalized version is zero.
• var c=dot(A,B); makes c the scalar dot product of A and B.
• var C=cross(A,B); makes C the right-handed cross product of A and B.

• scene is the main BABYLON.Scene object, created by PixAnvil every Reset. Most onscreen objects in Babylon.js take a scene as a constructor parameter.
• camera is the main viewport camera object, a BABYLON.ArcRotateCamera object, created by PixAnvil every run. You can change where the camera is looking toward, by calling camera.setTarget(vec3). You can change where the camera is looking from, by calling camera.setPosition(vec3), which gets translated as a target-relative location.
• scene is the main BABYLON.Scene object. Most objects need a scene as a constructor parameter.
• lib.createGround(zHeight,groundSize) creates a ground plane at the given Z axis height. By default an object at a height of Z=0.0 and a size of 1024 units is created. The object is returned, if you'd like to further adjust the position or orientation.
• lib.showAxes(size,parent) creates red (X axis), green (Y axis), and blue (Z axis) lines. Size is the length of the lines. Parent is the object used as the origin, or world origin if not defined.
• lib.showVector(direction,color,parent) creates a line pointing in this direction with this color. Color is a BABYLON.Color3. Parent is the object used as the origin, or world origin if not defined. Returns the newly created line mesh object.
• lib.tempVector(start,end,color) creates a line from start to end with this color. Color is a BABYLON.Color3. The line vanishes at the next frame unless redrawn.
• lib.tempBox(lo,hi,color) creates a 3D box with corners lo and hi, with this color. Color is a BABYLON.Color3. The box vanishes at the next frame unless redrawn.
• lib.dt is the time, in seconds, between animation frames. In UI, this value is the real wall clock time in seconds. In Loop, this value is scaled by the simulation time scale factor.
• lib.dt_avg is the average time, in real wall clock seconds, between animation frames.
• lib.time is the cumulative simulation time, in seconds. Internally it is updated by adding up lib.dt values.
• lib.screenw,lib.screenh are the window coordinates x,y pixel dimensions of the PixAnvil viewport.
• lib.mousex,lib.mousey are the window coordinates x,y pixel location of the mouse cursor onscreen.
• lib.mousedx,lib.mousedy are the change in x,y pixel coordinates since the last frame. These values are slightly smoothed to produce smooth animations even with jerky 30Hz mice.
• lib.mouseleft is a boolean value that is set to true if the left mouse button is down.
• lib.key is an ASCII-indexed array of boolean values, set to true if that ASCII keyboard key is currently pressed down. For example, lib.key['k'] is true if the k key is currently held down.
• lib.key_typed is an ASCII-indexed array of boolean values, set to true if that key has just been typed--either a key release, or a key repeat. The value will be true for exactly one Loop and one UI frame, then set to false again. /li>
• lib.key_toggle is ASCII-indexed an array of boolean values, initially false. Typing the corresponding key will toggle the state of the boolean from false to true or back again. This is useful for enabling or disabling simulation features.
• lib.wasd_camera(speed) moves the camera position using the W, A, S, and D keys, as well as Q and Z for up and down motion. The camera target is unchanged.
• PixAnvil.loadTab(tabName) returns a string of the data contained in the given tabName. This is useful for loading simulation data, or GLSL shaders.

• gl is the WebGL context.
• igloo is the Igloo base object.
• BABYLON_flush() clears BABYLON's cached program and bound vbos. You need to call this after running your own shaders or rendering offscreen.
• BABYLON_tex(texture) returns a BABYLON.RawTexture for this bare WebGLTexture. This is useful for drawing things offscreen with igloo or bare gl, but showing it onscreen with BABYLON.

O. Lawlor, ffosl@uaf.edu
CS, UAF