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## Vertical parallax scrolling

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### #1pulo  Members

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Posted 29 December 2012 - 07:00 AM

i have set up a simple 2D game with the help of the Platformer Starter-Kit for XNA. I have reworked the CameraCode (to have it in a own class with a transformation matrix). Now i want to have vertical parallax scrolling (it works fine horizontally) but i cannot get it to work vertically.
Here is how it is set up:

 private void ScrollCamera(Viewport viewport)
{

const float ViewMargin = 0.35f;

// Calculate the edges of the screen.
float marginHeight = viewport.Height * ViewMargin;
float marginTop = cameraPositionY + marginHeight;
float marginBottom = cameraPositionY + viewport.Height - marginHeight;

float marginWidth = viewport.Width * ViewMargin;
float marginLeft = cameraPositionX + marginWidth;
float marginRight = cameraPositionX + viewport.Width - marginWidth;

// Calculate how far to scroll when the player is near the edges of the screen.
float cameraMovementX = 0.0f;
if (Player.Position.X < marginLeft)
cameraMovementX = Player.Position.X - marginLeft;
else if (Player.Position.X > marginRight)
cameraMovementX = Player.Position.X - marginRight;

float cameraMovementY = 0.0f;
if (Player.Position.Y < marginTop)
cameraMovementY = Player.Position.Y - marginTop;
else if (Player.Position.Y > marginBottom)
cameraMovementY = Player.Position.Y - marginBottom;

// Update the camera position, but prevent scrolling off the ends of the level.
float maxCameraPositionY = Tile.Height * Height - viewport.Height;
float maxCameraPositionX = Tile.Width * Width - viewport.Width;
cameraPositionX = MathHelper.Clamp(cameraPositionX + cameraMovementX, 0.0f, maxCameraPositionX);
cameraPositionY = MathHelper.Clamp(cameraPositionY + cameraMovementY, 0.0f, maxCameraPositionY);
}

This function calculates the current position of the camera.

- "Height" = tiles.GetLength(1) where "tiles" is a 2D Array and
- "Width" = tiles.GetLength(0). So my world is represented in this 2D array
- Tile.Height and Tile.Width are the dimensions of my Tiles (i am currently working with tiles of the same size)

Now i am using this draw-call:

spriteBatch.Begin();
for (int i = 0; i <= EntityLayer; ++i)
layers[i].Draw(spriteBatch, camera._pos, i);
spriteBatch.End();

ScrollCamera(spriteBatch.GraphicsDevice.Viewport);
camera._pos = new Vector2(cameraPositionX, cameraPositionY);

spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.AlphaBlend, SamplerState.PointClamp, DepthStencilState.Default, RasterizerState.CullNone, null, camera.get_transformation(spriteBatch.GraphicsDevice));

DrawTiles(spriteBatch);

Player.Draw(gameTime, spriteBatch);

spriteBatch.End();

spriteBatch.Begin();

for (int i = EntityLayer + 1; i < layers.Length; ++i)
layers[i].Draw(spriteBatch, camera._pos, i);

spriteBatch.End();

I want to control the drawing process of the brackground layer seperately, like so:

 public void Draw(SpriteBatch spriteBatch, Vector2 cameraPosition, int index)
{
int segmentWidth = Textures[index].Width;
int segmentHeight = Textures[index].Height;

// Calculate which segments to draw and how much to offset them.
float x = cameraPosition.X * ScrollRate;
int leftSegment = (int)Math.Floor(x / segmentWidth);
int rightSegment = leftSegment + 1;
x = (x / segmentWidth - leftSegment) * -segmentWidth;

float y = cameraPosition.Y * ScrollRate;
int topSegment = (int)Math.Floor(y / segmentHeight);
y = (y / segmentHeight - topSegment) * -segmentHeight;

spriteBatch.Draw(Textures[leftSegment % Textures.Length], new Vector2(x, y + 136f), Color.White);
spriteBatch.Draw(Textures[rightSegment % Textures.Length], new Vector2(x + segmentWidth, y + 136f), Color.White);
}

Now i am pretty sure that there is problem with my calculation of my "y" but i cannot see it. Maybe someone can give me a hint or just a better way to approach this problem. Thanks a lot!

EDIT: Forgot to mention that it works fine for the tiles.

EDIT2: Sorry forgot to explain further: The Background Layers are scrolling nice horizontally but aren't aligned to the ground. They have an offset in the y-direction wich gets bigger and bigger depending on the total height of the level. I hope this clears some questions. If you still have some please let me know (i can also provide a screenshot if necessary) Thanks a lot

### #2pulo  Members

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Posted 31 December 2012 - 06:08 AM

Maybe someone could explain how he has done it? I am not sure how to approach this problem, so my "solution" could be very wrong.

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