On-the-fly terrain chunk generation - c++

Question

I'm writing an engine that can generate landscapes using noise functions, and load in new chunks as the player moves around the terrain. I spent the best part of two days figuring out how to place these chunks in the right position, so they don't overlap or get placed on top of existing chunks. It works well functionally, but there is a massive performance hit the further away you generate the chunks from the player (e.g. if you generate in a 3 chunk radius around the player, it's lighting fast, but if you increase that to a radius of 20 chunks it slows down very fast).
I know exactly why that is, but I can't think of any other way to do this. Before I go any further, here's the code I'm currently using, hopefully it's commented well enough to understand:
// Get the player's position rounded to the nearest chunk on the grid.
D3DXVECTOR3 roundedPlayerPos(SnapToMultiple(m_Dx->m_Camera->GetPosition().x, CHUNK_X), 0, SnapToMultiple(m_Dx->m_Camera->GetPosition().z, CHUNK_Z));
// Iterate through every point on an invisible grid. At each point, check if it is
// inside a circle the size of the grid (so we generate chunks in a circle around
// the player, not a square). At each point that is inside the circle, add a chunk to
// the ChunksToAdd vector.
for (int x = -CHUNK_RANGE-1; x <= CHUNK_RANGE; x++)
{
for (int z = -CHUNK_RANGE-1; z <= CHUNK_RANGE; z++)
{
if (IsInside(roundedPlayerPos, CHUNK_X*CHUNK_RANGE, D3DXVECTOR3(roundedPlayerPos.x+x*CHUNK_X, 0, roundedPlayerPos.z+z*CHUNK_Z)))
{
Chunk chunkToAdd;
chunkToAdd.chunk = 0;
chunkToAdd.position = D3DXVECTOR3((roundedPlayerPos.x + x*CHUNK_X), 0, (roundedPlayerPos.z + z*CHUNK_Z));
chunkToAdd.chunkExists = false;
m_ChunksToAdd.push_back(chunkToAdd);
}
}
}
// Iterate through the ChunksToAdd vector. For each chunk in this vector, compare it's
// position to every chunk in the Chunks vector (which stores each generated chunk).
// If the statement returns true, then there is already a chunk at that location, and
// we don't need to generate another.
for (i = 0; i < m_ChunksToAdd.size(); i++)
{
for (int j = 0; j < m_Chunks.size(); j++)
{
// Check the chunk in the ChunksToAdd vector with the chunk in the Chunks vector (chunks which are already generated).
if (m_ChunksToAdd[i].position.x == m_Chunks[j].position.x && m_ChunksToAdd[i].position.z == m_Chunks[j].position.z)
{
m_ChunksToAdd[i].chunkExists = true;
}
}
}
// Determine the closest chunk to the player, so we can generate that first.
// Iterate through the ChunksToAdd vector, and if the vector doesn't exist (if it
// does exist, we're not going to generate it so ignore it), compare the current (i)
// chunk against the current closest chunk. If it is larger, move on, and if it is
// smaller, store it's position as the new smallest chunk.
int closest = 0;
for (j = 0; j < m_ChunksToAdd.size(); j++)
{
if (!m_ChunksToAdd[j].chunkExists)
{
// Get the distance from the player to the chunk for the current closest chunk, and
// the chunk being tested.
float x1 = ABS(DistanceFrom(roundedPlayerPos, m_ChunksToAdd[j].position));
float x2 = ABS(DistanceFrom(roundedPlayerPos, m_ChunksToAdd[closest].position));
// If the chunk being tested is closer to the player, make it the new closest chunk.
if (x1 <= x2)
closest = j;
}
}
// After determining the position of the closest chunk, generate the volume and mesh, and add it
// to the Chunks vector for rendering.
if (!m_ChunksToAdd[closest].chunkExists) // Only add it if the chunk doesn't already exist in the Chunks vector.
{
Chunk chunk;
chunk.chunk = new chunkClass;
chunk.chunk->m_Position = m_ChunksToAdd[closest].position;
chunk.chunk->GenerateVolume(m_Simplex);
chunk.chunk->GenerateMesh(m_Dx->GetDevice());
chunk.position = m_ChunksToAdd[closest].position;
chunk.chunkExists = true;
m_Chunks.push_back(chunk);
}
// Clear the ChunksToAdd vector ready for another frame.
m_ChunksToAdd.clear();
(if it wasn't already obvious, this is run every frame.)
The problem area is to do with the CHUNK_RANGE variable. The larger this value, the more the first two loops are iterated through each frame, slowing the whole thing down tremendously. I need some advice or suggestions on how to do this more efficiently, thanks.
EDIT: Here's some improved code:
// Get the player's position rounded to the nearest chunk on the grid.
D3DXVECTOR3 roundedPlayerPos(SnapToMultiple(m_Dx->m_Camera->GetPosition().x, CHUNK_X), 0, SnapToMultiple(m_Dx->m_Camera->GetPosition().z, CHUNK_Z));
// Find if the player has changed into another chunk, if they have, we will scan
// to see if more chunks need to be generated.
static D3DXVECTOR3 roundedPlayerPosOld = roundedPlayerPos;
static bool playerPosChanged = true;
if (roundedPlayerPosOld != roundedPlayerPos)
{
roundedPlayerPosOld = roundedPlayerPos;
playerPosChanged = true;
}
// Iterate through every point on an invisible grid. At each point, check if it is
// inside a circle the size of the grid (so we generate chunks in a circle around
// the player, not a square). At each point that is inside the circle, add a chunk to
// the ChunksToAdd vector.
if (playerPosChanged)
{
m_ChunksToAdd.clear();
for (int x = -CHUNK_CREATE_RANGE-1; x <= CHUNK_CREATE_RANGE; x++)
{
for (int z = -CHUNK_CREATE_RANGE-1; z <= CHUNK_CREATE_RANGE; z++)
{
if (IsInside(roundedPlayerPos, CHUNK_X*CHUNK_CREATE_RANGE, D3DXVECTOR3(roundedPlayerPos.x+x*CHUNK_X, 0, roundedPlayerPos.z+z*CHUNK_Z)))
{
bool chunkExists = false;
for (int j = 0; j < m_Chunks.size(); j++)
{
// Check the chunk in the ChunksToAdd vector with the chunk in the Chunks vector (chunks which are already generated).
if ((roundedPlayerPos.x + x*CHUNK_X) == m_Chunks[j].position.x && (roundedPlayerPos.z + z*CHUNK_Z) == m_Chunks[j].position.z)
{
chunkExists = true;
break;
}
}
if (!chunkExists)
{
Chunk chunkToAdd;
chunkToAdd.chunk = 0;
chunkToAdd.position = D3DXVECTOR3((roundedPlayerPos.x + x*CHUNK_X), 0, (roundedPlayerPos.z + z*CHUNK_Z));
m_ChunksToAdd.push_back(chunkToAdd);
}
}
}
}
}
playerPosChanged = false;
// If there are chunks to render.
if (m_ChunksToAdd.size() > 0)
{
// Determine the closest chunk to the player, so we can generate that first.
// Iterate through the ChunksToAdd vector, and if the vector doesn't exist (if it
// does exist, we're not going to generate it so ignore it), compare the current (i)
// chunk against the current closest chunk. If it is larger, move on, and if it is
// smaller, store it's position as the new smallest chunk.
int closest = 0;
for (j = 0; j < m_ChunksToAdd.size(); j++)
{
// Get the distance from the player to the chunk for the current closest chunk, and
// the chunk being tested.
float x1 = ABS(DistanceFrom(roundedPlayerPos, m_ChunksToAdd[j].position));
float x2 = ABS(DistanceFrom(roundedPlayerPos, m_ChunksToAdd[closest].position));
// If the chunk being tested is closer to the player, make it the new closest chunk.
if (x1 <= x2)
closest = j;
}
// After determining the position of the closest chunk, generate the volume and mesh, and add it
// to the Chunks vector for rendering.
Chunk chunk;
chunk.chunk = new chunkClass;
chunk.chunk->m_Position = m_ChunksToAdd[closest].position;
chunk.chunk->GenerateVolume(m_Simplex);
chunk.chunk->GenerateMesh(m_Dx->GetDevice());
chunk.position = m_ChunksToAdd[closest].position;
m_Chunks.push_back(chunk);
m_ChunksToAdd.erase(m_ChunksToAdd.begin()+closest);
}
// Remove chunks that are far away from the player.
for (i = 0; i < m_Chunks.size(); i++)
{
if (DistanceFrom(roundedPlayerPos, m_Chunks[i].position) > (CHUNK_REMOVE_RANGE*CHUNK_X)*(CHUNK_REMOVE_RANGE*CHUNK_X))
{
m_Chunks[i].chunk->Shutdown();
delete m_Chunks[i].chunk;
m_Chunks[i].chunk = 0;
m_Chunks.erase(m_Chunks.begin()+i);
}
}

Answer 1

Have you tried profiling it to work out exactly where the bottleneck is?
Do you need to check all of those chunks or could you get away with checking the direction the player is looking and only generate the ones in view?
Is there any reason why you draw the chunk closest to the player first if you're generating it all once per frame before displaying it? Skipping the stage where you sort them may free up a bit of processing power.
Is there any reason you couldn't combine the first two loops to just create a vector of chunks which need generating?

Answer 2

It sounds like you're trying to do too much work (i.e. building chunks) on the render thread. If you can do the work of a three chunk radius really fast you should limit it to that per frame. How many chunks are you trying to generate, in each situation, per frame?
I'm going to assume that generating each chunk is independent, therefore, you can probably move the work to another thread - then show the chunk when it is ready.