Discuss about `rvx, rvy` in `collection-map.js`

[finscn]

Discuss about rvx, rvy in collection-map.js

there is a function with arguments named rvx, rvy , What do they mean? what's the full name ?

Impact/lib/impact/collision-map.js

Line 63 in 7768fd2

_traceStep: function( res, x, y, vx, vy, width, height, rvx, rvy, step ) {

---

the _traceStep() be called with vx & vy

Impact/lib/impact/collision-map.js

Line 44 in 7768fd2

this._traceStep( res, x, y, sx, sy, objectWidth, objectHeight, vx, vy, i );

Why do you pass vx , vy ? in my opinion , at line 44 , It should pass sx ,sy

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the function _traceStep has arguments rvx, rvy , and pass them into _checkTileDef()

Impact/lib/impact/collision-map.js

Line 95 in 7768fd2

this._checkTileDef(res, t, x, y, rvx, rvy, width, height, prevTileX, tileY)

Impact/lib/impact/collision-map.js

Line 104 in 7768fd2

(t > 1 && this._checkTileDef(res, t, x, y, rvx, rvy, width, height, tileX, tileY)) // slope?

Impact/lib/impact/collision-map.js

Line 142 in 7768fd2

this._checkTileDef(res, t, x, y, rvx, rvy, width, height, tileX, prevTileY) ) {

Impact/lib/impact/collision-map.js

Line 150 in 7768fd2

(t > 1 && this._checkTileDef(res, t, x, y, rvx, rvy, width, height, tileX, tileY)) // slope?

Why do you pass rvx , rvy ? in my opinion , at line 44 , It should pass vx ,vy.

---

I post a PR , Just for comparing the differences in the code

https://github.com/phoboslab/Impact/pull/100/files

If change the code to my version, will there be any problems?

[Joncom]

Maybe "rvx" means "reference to vx", since the value appears to come from "vx" on line 44.

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-------- Original Message --------

On 3/25/25 9:46 PM, finscn wrote: Discuss about rvx, rvy in collection-map.js there is a function with arguments named rvx, rvy , What do they mean? what's the full name ? https://github.com/phoboslab/Impact/blob/7768fd29c70ca924a78673d93081baab5a72fbe6/lib/impact/collision-map.js#L63 _traceStep : function ( res , x , y , vx , vy , width , height , rvx , rvy , step ) --------------------------------------------------------------- the _traceStep() be called with vx & vy https://github.com/phoboslab/Impact/blob/7768fd29c70ca924a78673d93081baab5a72fbe6/lib/impact/collision-map.js#L44 this . _traceStep ( res , x , y , sx , sy , objectWidth , objectHeight , vx , vy , i ) ; Why do you pass vx , vy ? in my opinion , at line 44 , It should pass sx ,sy --------------------------------------------------------------- the function _traceStep has arguments rvx, rvy , and pass them into _checkTileDef() https://github.com/phoboslab/Impact/blob/7768fd29c70ca924a78673d93081baab5a72fbe6/lib/impact/collision-map.js#L95 _traceStep: function ( res , x , y , vx , vy , width , height , rvx , rvy , step ) { // ...... this . _checkTileDef ( res , t , x , y , rvx , rvy , width , height , tileX , tileY ) // ...... } Why do you pass rvx , rvy ? in my opinion , at line 44 , It should pass vx ,vy. — Reply to this email directly, [view it on GitHub](#99), or [unsubscribe](https://github.com/notifications/unsubscribe-auth/AAMXA25HTIDBSKGPG3DGQTD2WFT5NAVCNFSM6AAAAABZX2PXHSVHI2DSMVQWIX3LMV43ASLTON2WKOZSHE2DMNZZGU4TGMA). You are receiving this because you are subscribed to this thread.Message ID: ***@***.***> [finscn]finscn created an issue [(phoboslab/Impact#99)](#99) Discuss about rvx, rvy in collection-map.js there is a function with arguments named rvx, rvy , What do they mean? what's the full name ? https://github.com/phoboslab/Impact/blob/7768fd29c70ca924a78673d93081baab5a72fbe6/lib/impact/collision-map.js#L63 _traceStep : function ( res , x , y , vx , vy , width , height , rvx , rvy , step ) --------------------------------------------------------------- the _traceStep() be called with vx & vy https://github.com/phoboslab/Impact/blob/7768fd29c70ca924a78673d93081baab5a72fbe6/lib/impact/collision-map.js#L44 this . _traceStep ( res , x , y , sx , sy , objectWidth , objectHeight , vx , vy , i ) ; Why do you pass vx , vy ? in my opinion , at line 44 , It should pass sx ,sy --------------------------------------------------------------- the function _traceStep has arguments rvx, rvy , and pass them into _checkTileDef() https://github.com/phoboslab/Impact/blob/7768fd29c70ca924a78673d93081baab5a72fbe6/lib/impact/collision-map.js#L95 _traceStep: function ( res , x , y , vx , vy , width , height , rvx , rvy , step ) { // ...... this . _checkTileDef ( res , t , x , y , rvx , rvy , width , height , tileX , tileY ) // ...... } Why do you pass rvx , rvy ? in my opinion , at line 44 , It should pass vx ,vy. — Reply to this email directly, [view it on GitHub](#99), or [unsubscribe](https://github.com/notifications/unsubscribe-auth/AAMXA25HTIDBSKGPG3DGQTD2WFT5NAVCNFSM6AAAAABZX2PXHSVHI2DSMVQWIX3LMV43ASLTON2WKOZSHE2DMNZZGU4TGMA). You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[Joncom]

Regarding your pull request, the _traceStep function takes 10 arguments, so I don't know why you're deleting arguments from your calls. You're passing too few arguments (only 8). Why are you doing that?

[finscn]

Regarding your pull request, the _traceStep function takes 10 arguments, so I don't know why you're deleting arguments from your calls. You're passing too few arguments (only 8). Why are you doing that?

because I think rvx rvy is useless , I removed them from _traceStep()'s definition

[Joncom]

If it is true that they are useless, then those arguments would need to be removed from the function signature too. Why are they useless though?

[phoboslab]

rvx and rvy ist the "real velocity".

_traceStep is called like this:

Impact/lib/impact/collision-map.js

Lines 40 to 44 in 7768fd2

	var sx = vx / steps;
	var sy = vy / steps;
	for( var i = 0; i < steps && (sx || sy); i++ ) {
	this._traceStep( res, x, y, sx, sy, objectWidth, objectHeight, vx, vy, i );

This is passing the velocity for one step (sx, sy named vx, vy in _traceStep) and the real/full velocity of the object (vx, vy named rvx, rvy in _traceStep). The real velocity is not needed for collision detection, but later (in checkTileDef) for resolving the collision.

Simple example: you hit the ground at an angle. The resolved y position will be the impact position, the x position however will incorporate the x velocity, essentially sliding you over the ground. Here the real x velocity is needed, not the x velocity for just one step of collision detection.

[finscn]

@phoboslab thanks .
but if use real/full velocity , the target point ( x+ rvy , y+ rvy) or it's pedal may be out of the slope-tile's bounding .

should we use the red point ?