Performance issue using for loop in script

pjmendes · 2010-04-10T18:51:59

Hi all, While attempting to implement a tile map system in AS, I met with the following issue: running a single for loop (withouth any code inside) will make my framerate drop considerably (from about 500 to 30 fps); accessing and calling values inside a single dimensional or multi-dimensional array (containing handles to classes defined script-side), will drop the framerate to unusable levels. (Project has been compiled in "Release" mode). Am I doing something wrong, or is AngelScript not supposed to be used this way? Any recomendations? How I'm defining my "for" loops: uint totalTilesX = 300; // small test value, will be used a much larger value in-game uint totalTilesY = 10; uint totalTiles = this.totalTilesX * this.totalTilesY; for(uint idxTile = 0; idxTile < totalTiles; ++idxTile) {} Script classes definitions and calling methods: TileMap structure: class TileMap { TileMap(uint totalTilesX, uint totalTilesY, uint tileWidth, uint tileHeight) { this.totalTilesX = totalTilesX; this.totalTilesY = totalTilesY; this.tileWidth = tileWidth; this.tileHeight = tileHeight; this.totalLayers = 10; // Resize it to desired dimension this.tileMap.resize(this.totalTilesX * this.totalTilesY); } // this function is called once every cycle, contains several for loops and behaves very poorly void update(float timeSinceLastFrame) // update tile properties { // Test: contains the loop code above } void addTile(Tile@ tile, uint tileX, uint tileY, uint layerIndex) // tile and tilemap x,y and layer coordinates { @this.tileMap[tileY * this.totalTilesY + tileX] = tile; } void drawTilemapGrid() { // draw column lines for(uint idxColumn = 0; idxColumn <= this.totalTilesX; ++idxColumn) { Vector2 lineStart(idxColumn * tileWidth, 0); Vector2 lineEnd(idxColumn * tileWidth, totalTilesY * tileHeight); basicEngine.drawLine(lineStart, lineEnd, 1.0f, 0, 0, 255, 255); } // draw row lines for(uint idxLine = 0; idxLine <= this.totalTilesY; ++idxLine) { Vector2 lineStart(0, idxLine * tileHeight); Vector2 lineEnd(totalTilesX * tileWidth, idxLine * tileHeight); basicEngine.drawLine(lineStart, lineEnd, 1.0f, 0, 0, 255, 255); } } // properties Tile@[] tileMap; uint totalTilesX; uint totalTilesY; uint tileWidth; uint tileHeight; uint totalLayers; } Definitions of array structure: Tile@[] tileMap; // also tried "Tile@[][]", to a worse performance when accessing inside loops Tile class (contains another script defined class named "Sprite") class Tile { Tile(Vector2 position, Sprite@ sprite) // The default constructor { this.position = position; @this.sprite = sprite; } ~Tile() {} void resetHasUpdated() { this.sprite.hasUpdated = false; } void update(float timeSinceLastUpdate) { if(!this.sprite.hasUpdated) { this.sprite.imageSprite.update(timeSinceLastUpdate); // update animation state this.sprite.hasUpdated = true; } } void draw(Vector2 tileOffset) { this.sprite.imageSprite.setPosition(this.position + tileOffset); this.sprite.imageSprite.draw(); } // class properties Vector2 position; // x,y position of sprite within tile Sprite@ sprite; // reference sprite to draw as tile } [Edited by - pjmendes on April 2, 2010 11:22:54 PM]

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Started by pjmendes April 02, 2010 08:55 PM

10 comments, last by pjmendes 14 years, 7 months ago

WitchLord

4,860

April 10, 2010 02:20 PM

Hmm, your loops are accessing the script class members for each iteration. This may be the cause. Can you try rewriting the function like this:

    void update(float timeSinceLastFrame)   // update tile properties    {        uint totalTilesX = this.totalTilesX;        uint totalTilesY = this.totalTilesY;        for(uint idxColumn = 0; idxColumn < totalTilesX; ++idxColumn)        {            for(uint idxLine = 0; idxLine < totalTilesY; ++idxLine)            {            }        }        for(uint idxColumn = 0; idxColumn < totalTilesX; ++idxColumn)        {            for(uint idxLine = 0; idxLine < totalTilesY; ++idxLine)            {            }        }    }

This is likely going to give a great performance boost. Local variables are always the most efficient to access, as they are referencable directly by the op codes in the VM. Class members and global variables need sevaral steps to get to the final value.

I'll definitely look into optimizing the bytecode instructions to reduce the amount of steps needed for the VM to access the class members, but it will never be as quick as the local variables. So the above suggestion will always be valid.

Regards,
Andreas

AngelCode.com - game development and more - Reference DB - game developer references
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pjmendes

Author

100

April 10, 2010 06:51 PM

Indeed there is some improvement in referencing local variables following your suggestion (about 10% from a quick glance). However, since my tilemap implementation does a heavy use of accessing script class members inside several loops, the performance goes down too much for me to be able to implement this part in AngelScript, so I plan on moving it application-side.

I will keep this in mind when designing my engine, critical areas will not be done script-side, but I still wish to use the great power of AngelScripts (possibly for AI, each AI entity calling script callbacks).

Thanks for all the help, and for creating and improving and providing us with AngelScript!

Game Development Blog: http://pjmendes.blogspot.com/

Performance issue using for loop in script

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