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sandorlev

Segmentation fault while rendering map

2 posts in this topic

I'm trying to render a map with a moving camera and I get a segmentation fault every time I start moving down. Here is the code:

[CODE]
void Map::Render(SDL_Surface* tileSet, SDL_Surface* display) const
{
const int tileSize = Tile::GetTileSize();
Vector2D cameraLocation = Camera::control.GetLocation();

//Checking boundaries
if (cameraLocation.x < 0)
cameraLocation.x = 0;

else if (cameraLocation.x > width * tileSize)
cameraLocation.x = width * tileSize;

if (cameraLocation.y < 0)
cameraLocation.y = 0;

else if (cameraLocation.y > height * tileSize)
cameraLocation.y = height * tileSize;

Vector2D first;
first.x = (int)cameraLocation.x / tileSize;
first.y = (int)cameraLocation.y / tileSize;

Vector2D offset;
offset.x = (int)cameraLocation.x % tileSize;
offset.y = (int)cameraLocation.y % tileSize;

for (int y=0; y<height; y++)
{
for (int x=0; x<width; x++)
{
//Segmentation fault happens here
const int index = \
rows[y + first.y].columns[x + first.x].GetTileID();

Rectangle srcRect = Tile::GetSourceRect(index);
const int xOffset = x * tileSize - offset.x;
const int yOffset = y * tileSize - offset.y;
Surface::Blit(xOffset, yOffset, srcRect, tileSet, display);
}
}
}
[/CODE]

The segmentation fault happens at the GetTileID() function. Additional data:

[CODE]
width = 50;
height = 200;
tileSize = 96;

//Variable values when the segmentation fault happens
cameraLocation.x = 10;
cameraLocation.y = 100;


first.x = 0;
first.y = 1;

offset.x = 10;
offset.y = 4;


x = 9;
y = 198;

xOffset = 854;
yOffset = 19004;
[/CODE]
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Sorry, I am not convenient with SDL, but I can recommend you to split the problematic line into pieces to simplify debugging.
You can evaluate:
rows[y + first.y]
columns[x + first.x]
GetTileID();
separately to see what gives you SIGSEGV.

Also I would be interesting to see what are the classes for rows and columns objects and if the values passed to their [] operator are valid.
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Assuming rows has height indices, I believe the problem is related to setting first.y to the last tile (if you are at the bottom, first.y will be height), and then adding numbers to height, and attempting to access row at a value past height.

So, when you do this:
[code]
for (int y=0; y<height; y++) {
...
const int index =
rows[y + first.y].columns[x + first.x].GetTileID();
[/code]
After the 1st loop, y will be 1, y+first.y = height+1, which is out of bounds of the array rows. You need to re-think how to display the map.
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