Topics

1

Graphics / Conversion from Box2D to SFML creates gap

« on: April 22, 2016, 09:01:18 pm »

I have the following bit of code, which basically takes a Box2D world and converts it to SFML shapes that are then drawn to the screen. For rectangles, this works perfectly, but for other polygons, it produces a strange gap between the object and it's representation in Box2D which manifests as a gap between objects on screen. Can anyone see why this might be the case?

b2PolygonShape* polyShape = (b2PolygonShape*) bodyFixture->GetShape();

ConvexShape shapeToFill;
shapeToFill.setPosition(body->GetWorldCenter().x*SCALE, body->GetWorldCenter().y*SCALE);

int vertCount = polyShape->GetVertexCount();
shapeToFill.setPointCount(vertCount);

for(int vert = 0 ; vert < vertCount ; vert++) {
   b2Vec2 aVertex = polyShape->GetVertex(vert);
   sf::Vector2f sfVect;
   sfVect.x = aVertex.x*SCALE;
   sfVect.y = aVertex.y*SCALE;
   shapeToFill.setPoint(vert,sfVect);
}
shapeToFill.setRotation(180/b2_pi * body->GetAngle());
 

UPDATE, SOLVED: The problem lay with this line:

shapeToFill.setPosition(body->GetWorldCenter().x*SCALE, body->GetWorldCenter().y*SCALE);

which needed to be changed to:

shapeToFill.setPosition(body->GetPosition().x*SCALE, -body->GetPosition().y*SCALE);

The world center of a body is not it's centroid, but it's local origin.

2

Window / sf::Mouse::getPosition slightly off

« on: April 20, 2016, 07:56:18 pm »

I'm using:
   sf::Vector2i pixelPos = sf::Mouse::getPosition(*this);
   sf::Vector2f worldPos = this->mapPixelToCoords(pixelPos);
to get the position of mouse clicks within a world. When I draw draw things based on these coordinates, everything is drawing slightly higher than where the mouse actually was. This is consistent no matter how I change the view, it's always off by the same amount. If I resize the window, it's off in both axis' by more, consistently. I know this is somewhat vague, as the code for the window is spread out across three or four classes. I'm just wondering if there is a sample program out there that deals with window resizes so I can see what's going on. Thanks!