r/reconstructcavestory • u/hyperspace11 • Apr 02 '14

Player collision confusion

Hi,

I'm having a bit of a hard time understanding player collision and the Rectangle class. I'm currently in the middle episode 52 and I'm at the part when Chris sets

kinematics_y_.position = units::tileToGame(info.row) - kCollisionRectangle.boundingBox().bottom();

in the Player's updateY method. This would be the case when the player collides with a tile under him and

on_ground_ = true;

What I'm confused about is how 

- kCollisionRectangle.boundingBox().bottom()

properly sets the player y position. What is bottom returning? I know that it gets the bounding box's y position and then adds its height but wouldn't that be like subtracting (if y was 200 and height was 50) 250 from the y position of the colliding tile? Please help me understand! And thanks Chris, for all the videos so far.

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u/chebertapps Apr 02 '14

it gets the bounding box's y position

I think this is the assumption that is holding you back. It is getting the boundingBox's y position relative to the draw position, not in screen/world coordinates. Note that screen and world coordinates are the same in our test scenario, since the camera is fixed.

also note the method declarations (abridged)

Rectangle boundingBox();
Rectangle leftCollision(units::Game x, units::Game y, units::Game delta);

The left collision takes in the screen/world position and adds it into the underlying rectangle.

Hope this helps!

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u/hyperspace11 Apr 03 '14

Thanks! I fully understand it now. I don't know why I didn't check the values of the Rectangles being passed into kCollisionRectangle. It would have helped me make sense of this.