Lightning Sprite Position Issue

[EdBoon]

I am trying to implement a lightning gun into my shooter. It seems I have something wrong in the math because the contact points which should one be in the center of the player and another the center of the closest enemy are not right.

Here is the function i call to get the closest enemy in from a quad tree call: (probably don't need to look at this section of code to understand my question, added it just in case)

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public Vector2 findClosestEnemy()
        {
            List<QT.IQuadTreeItem> collideItems = new List<QT.IQuadTreeItem>(10);

            collideItems.Clear();
            QT.FloatRectangle range = new QT.FloatRectangle(bounds.X - 200, bounds.Y- 200, 400, 400);
            Game1.quadTree.Query(range, ref collideItems);
            Vector2 closest = new Vector2 (100);
            closestDistance = 1000;

            Vector2 mapPos = position - Game1.mapOffset;
                Vector2 itemPosition = new Vector2(
                        mapPos.X + BoundingBox.Width / 2f,
                        mapPos.Y + BoundingBox.Height / 2f);
                float itemRadius = BoundingBox.Width / 2f;



            foreach (Actors.Enemies.Zombie item in (collideItems.OfType<Actors.Enemies.Zombie>()))
            {

                Vector2 item2Position = new Vector2(
                    item.BoundingBox.X + item.BoundingBox.Width / 2f,
                    item.BoundingBox.Y + item.BoundingBox.Height / 2f);


                if (Vector2.Distance(itemPosition, item2Position) < closestDistance)
                {
                    closestDistance = Vector2.Distance(itemPosition, item2Position);
                    closest = new Vector2(item.bounds.X, item.bounds.Y);
                    lightningTarget = item;

                    toTarget = new Vector2((item.bounds.X + item.BoundingBox.Width/2) - (this.bounds.X + BoundingBox.Width/2),
                                            (item.bounds.Y + item.BoundingBox.Height/2) - (this.bounds.Y + BoundingBox.Height/2));
                    toTarget.Normalize();

                    lightningRotation = (float)Math.Atan2(toTarget.Y, toTarget.X) + (float)Math.PI / 2;
                }
            }

            if (closest == new Vector2(100))
            {
                return new Vector2(0);
            }
            else
            {
                return closest;
            }
        }

And this is what I use to draw the lightning:

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if (fireLightning == true)
                {
                    int lightFrame = gunFrame / 3;
                    Game1.spriteBatch.Draw(Game1.teslaTexture[lightFrame], 
                                            new Vector2 (bounds.X - toTarget.X/2, bounds.Y - toTarget.Y/2), 
                                            null, 
                                            Color.White,
                                            lightningRotation + (float)Math.PI/2,
                                            new Vector2((bounds.X + BoundingBox.Width/2) + toTarget.X / 2, (bounds.Y + BoundingBox.Height/2) + toTarget.Y / 2), 
                                            closestDistance/467, 
                                            SpriteEffects.None, 0.0f);
                    gunFrame++;
                    if (gunFrame >= 30)
                        gunFrame = 0;
                }

You will notice it is in XNA and for referrence the draw function is:

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SpriteBatch.Draw (Texture2D, Vector2, Nullable<Rectangle>, Color, Single, Vector2, Vector2, SpriteEffects, Single)

the important part is the first vector2 (location to draw) and the second vector2 (the center of the image)
bounds.x and bounds.y are my position minus the map offset from scrolling

The problem is the first vector2, and I realize it is not right at all how I am doing it. bounds.x minus a normalized vector facing the enemy. It doesnt make sense. Can anyone help me out here on the location. i cant just put the center of the player as the location because the top left corner of the image will be placed at the center and thats wrong. I need the middle/left edge to always be in the center of the player. Also the center of the Right edge at the middle of the enemy sprite.

video added to show how it works with the code above:



and as always, thank guys!

[Falco Girgis]

Can you try to explain what the two vector arguments are exactly? I'm still a little fuzzy on the arguments your SpriteBatch.Draw() is expecting.

[avansc]

It looks like a scaling issue.
I dont know how you make the lightning, whether its procedural, or just a script, but when you scale it you are not offsetting appropriately. You can see this in the fact that it gets worse when the lightning has to "shoot" further, IE as your scaling goes up.

[MadPumpkin]

It looks like a scaling issue.
I dont know how you make the lightning, whether its procedural, or just a script, but when you scale it you are not offsetting appropriately. You can see this in the fact that it gets worse when the lightning has to "shoot" further, IE as your scaling goes up.

First of all this is awesome, great work. Second, I agree with Avansc. It's awesome you noticed that, I didn't even realize it.

[Falco Girgis]

It looks like a scaling issue.
I dont know how you make the lightning, whether its procedural, or just a script, but when you scale it you are not offsetting appropriately. You can see this in the fact that it gets worse when the lightning has to "shoot" further, IE as your scaling goes up.

First of all this is awesome, great work. Second, I agree with Avansc. It's awesome you noticed that, I didn't even realize it.

Are you guys serious? You do realize that this is the entire reason he made the post to begin with? He specifically said that he is trying to calculate contact points (to derive position and scale for the sprite) based on the distance between the player and target... No shit his lighting offset is incorrect. Very astute of you, gentlemen!

[EdBoon]

Can you try to explain what the two vector arguments are exactly? I'm still a little fuzzy on the arguments your SpriteBatch.Draw() is expecting.

the first vector is where to set the rotation axis of the sprite, and the second Vector argument is for the location to actually display the sprite, this helps because the rotation axis can be outside of the sprite which allows items to look like they are revolving around another object (should have been my first hint on a solution). My problem was i was trying to set the rotation axis half way in-between the player and the target as well as trying to find the right rotation so the sprite direction would look correct, which thinking back is absolutely retarded. It was a very simple fix, i set the rotation axis (first vector) to the center of the player, and the second vector (sprite location) to half of the height of the lightning picture away from the players gun (the lightning is in the middle of the picture). The rotation was easy just using the vector from the player to the target.

I added the correct code below in case anyone ever needs it

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Game1.spriteBatch.Draw(Game1.teslaTexture[lightFrame],
                                                new Vector2((bounds.X), (bounds.Y)),//bounds of the player which are updated each frame as player.position-mapOffset
                                                null,
                                                Color.White,
                                                lightningRotation , //shown below the Draw function
                                                new Vector2(Game1.teslaTexture[0].Width / 2, Game1.teslaTexture[0].Height + texture.Width * 2f / 5f), //2/5 so it starts under the gun leaving no gap between the gun and the lightning
                                                closestDistance / 467, //closest distance is the distance to the closest enemy and 467 is the length of the lightning sprite , this is so it scales to the correct size 
                                                SpriteEffects.None, 0.0f);

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public Vector2 findClosestEnemy()
        {
            List<GameEntity> listofguys = Game1.gridmap.getItemsInGrid(new Vector2(position.X - 200, position.Y - 200), new Vector2(position.X + 200, position.Y + 200)); //no longer using quadtree, switched to spatial hashing so i could handle more enemies on screen, this just gets a list of the ones near the player

            Vector2 closest = new Vector2 (100);
            closestDistance = 1000;

            Vector2 mapPos = position - Game1.mapOffset;
                Vector2 itemPosition = new Vector2(
                        mapPos.X + bounds.Width / 2f,
                        mapPos.Y + bounds.Height / 2f);
                float itemRadius = bounds.Width / 2f;

            foreach (Actors.Enemies.Enemy item in listofguys.OfType<Actors.Enemies.Enemy>()) //gross, foreach statement, need to change that
            {
                Vector2 item2Position = new Vector2(
                    item.bounds.X + item.bounds.Width / 2f,
                    item.boundsBox.Y + item.boundsBox.Height / 2f);

                if (Vector2.Distance(itemPosition, item2Position) < closestDistance && item.gameItemType != 1)
                {
                    closestDistance = Vector2.Distance(itemPosition, item2Position); //player and target positions
                    closest = new Vector2(item.bounds.X, item.bounds.Y); // bounds is position-mapoffset
                    lightningTarget = item;

                    toTarget = new Vector2((item.bounds.X + item.boundsBox.Width / 2) - (this.bounds.X + boundsBox.Width / 2),
                                            (item.bounds.Y + item.boundsBox.Height / 2) - (this.bounds.Y + boundsBox.Height / 2));
                    
                    toTarget.Normalize();

                    lightningRotation = (float)Math.Atan2(toTarget.Y, toTarget.X) + (float)Math.PI / 2;
                }
            }

            if (closest == new Vector2(100))
            {
                return new Vector2(0);
            }
            else
            {
                return closest;
            }
        }