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
_______________________________________________
es-discuss mailing list
es-discuss@mozilla.org
https://mail.mozilla.org/listinfo/es-discuss
