On May 12, 2016, at 1:53 PM, Brian Barnes<gga...@charter.net> wrote:
Not by my testing, at least.
My original example is a simple one to explain what the procedure is.
Here’s a more complex example, from my code, from my mesh classes. This
function updates the vertices in the mesh based on the position of the bones
of a skeleton, it gets called every frame for every model mesh that can be
seen in the scene:
updateVertexesToPoseAndPosition(view,skeleton,angle,position)
{
var n,v;
var bone,parentBone;
// move all the vertexes
var vIdx=0;
var nIdx=0;
for (n=0;n!==this.vertexCount;n++) {
v=this.vertexList[n];
// bone movement
bone=skeleton.bones[v.boneIdx];
this.rotVector.setFromPoint(v.vectorFromBone);
this.rotVector.rotate(bone.curPoseAngle);
this.rotVector.x=bone.curPosePosition.x+this.rotVector.x;
this.rotVector.y=bone.curPosePosition.y+this.rotVector.y;
this.rotVector.z=bone.curPosePosition.z+this.rotVector.z;
this.rotNormal.setFromPoint(v.normal);
this.rotNormal.rotate(bone.curPoseAngle);
// average in any parent movement
if (v.parentBoneIdx!==-1) {
parentBone=skeleton.bones[v.parentBoneIdx];
this.parentRotVector.setFromPoint(v.vectorFromParentBone);
this.parentRotVector.rotate(parentBone.curPoseAngle);
this.parentRotVector.x=parentBone.curPosePosition.x+this.parentRotVector.x;
this.parentRotVector.y=parentBone.curPosePosition.y+this.parentRotVector.y;
this.parentRotVector.z=parentBone.curPosePosition.z+this.parentRotVector.z;
this.parentRotNormal.setFromPoint(v.normal);
this.parentRotNormal.rotate(parentBone.curPoseAngle);
this.rotVector.average(this.parentRotVector);
this.rotNormal.average(this.parentRotNormal);
}
// whole model movement
this.rotVector.rotate(angle);
this.drawVertices[vIdx++]=this.rotVector.x+position.x;
this.drawVertices[vIdx++]=this.rotVector.y+position.y;
this.drawVertices[vIdx++]=this.rotVector.z+position.z;
this.rotNormal.rotate(angle);
this.drawNormals[nIdx++]=this.rotNormal.x;
this.drawNormals[nIdx++]=this.rotNormal.y;
this.drawNormals[nIdx++]=this.rotNormal.z;
}
// set the buffers
var gl=view.gl;
gl.bindBuffer(gl.ARRAY_BUFFER,this.vertexPosBuffer);
gl.bufferData(gl.ARRAY_BUFFER,this.drawVertices,gl.DYNAMIC_DRAW);
gl.bindBuffer(gl.ARRAY_BUFFER,this.vertexNormalBuffer);
gl.bufferData(gl.ARRAY_BUFFER,this.drawNormals,gl.STATIC_DRAW);
}
Notice that rotVector, rotNormal, parentRotVector, and parentRotNormal,
are all “this”, i.e., globals. They are *only* used in this function, no
where else in the class. If I put them as local variables, I get enormous
GC pauses. If I don’t, I get none (granted, I have to do this everywhere,
so it’s just not this function.)
The example I gave existed only to show how it would work; not a real
example. Here’s a real example, that shows obvious problems with local
variables. Yes, these are objects.
Not that moving the objects would ONLY be something that happened at
compile time and would be a hint; they wouldn’t be effected in the warm up
runs. You’d almost have to say that same hint would force a compile (which
has it’s own problems.)
[>] Brian
On May 12, 2016, at 1:33 PM, Allen Wirfs-Brock<al...@wirfs-brock.com>
wrote:
On May 12, 2016, at 9:39 AM, Brian Barnes<gga...@charter.net> wrote:
...
If I call doSomething a lot of times, I get a lot of objects to be
tracked and GC’d. Yes, I can rewrite that code to obviously eliminate them,
but pretend there is actually something interesting happening here that
requires those variables. And engines can be smart enough to mark them and
deal with them with the function ends (I don’t know if this is done.)
What I’m thinking is some kind of class based hint that would “super”
hoist all local function variables. It would be sugar but it would
transform it into:
Local variables like a,b,c in your example are probably the least
expensive construct in JS. In your example, there are no objects created by
doSomething, not state that persists after doSomething returns, and no GC
pressure. Anything you do WRT moving such local state into object properties
is going to be more expensive.
Allen
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