[Adonthell-devel] Precision issue?

[Kai Sterker]

While debugging worldtest some more, I came across the following:

Breakpoint 1, world::moving::update_position (this=0x371ce0) at
../../../adonthell/src/world/moving.cc:247
247         vector3<float> finalPosition = execute_move
(&collisionData);
(gdb) print eRadius
$1 = {
  X = 20,
  Y = 12.5,
  Z = 40
}
Current language:  auto; currently c++
(gdb) print eSpacePosition
$2 = {
  X = 9,
  Y = 12.8000002,
  Z = 1.125
}

Instead of of being 12.8, eSpacePosition end up being 12.8 and a wee
bit more. While this doesn't seem like a big thing, it could corrupt
the character location in the long run.

Another thing, after adding some more debugging output to see
character location, the tiles being checked for collision and the
point where collisions occur, the following was the result:

// first iteration: no collision as character is not moving
    pos [185.000, 200.000, 40.000]
   area [165, 188, 0] - [205, 213, 80]
  shape [120, 140, -5] - [180, 200, 0]
  shape [180, 140, -5] - [240, 200, 0]
  shape [120, 200, -5] - [180, 260, 0]
  shape [180, 200, -5] - [240, 260, 0]
// second iteration: gravity
    pos [185.000, 200.000, 40.000] <-- center of the character sprite
   area [165, 188, 0] - [205, 213, 80] <-- area checked for collision
  shape [120, 140, -5] - [180, 200, 0] <-- 1st tile
    col [180.000, 200.000, 0.000] dist 0.03175
    col [180.000, 200.000, 0.000] dist 0.03175
  shape [180, 140, -5] - [240, 200, 0] <-- 2nd tile
  shape [120, 200, -5] - [180, 260, 0] <-- 3rd tile
  shape [180, 200, -5] - [240, 260, 0] <-- 4th tile
    col [181.404, 201.404, 0.000] dist 0.02273
    col [181.404, 201.404, 0.000] dist 0.02273
    col [184.167, 200.000, -0.347] dist 0.00955 <-- closest collision
on 4th tile

What I had expected would be a collision at [185, 200, 0] with
distance 0 as that is the point the character rests on. It would be
interesting to see the same figures for the working alpha-2 code for
comparison, so here they are:

    pos [25.000, 0.500, 40.000]
   area [165, 188, 0] - [245, 253, 80]
  shape [180, 140, -5] - [240, 200, 0]
  shape [120, 140, -5] - [180, 200, 0]
  shape [180, 200, -5] - [240, 260, 0]
  shape [120, 200, -5] - [180, 260, 0]
  shape [180, 140, -5] - [240, 200, 0]
  shape [180, 200, -5] - [240, 260, 0]
    pos [25.000, 0.500, 40.000]
   area [165, 188, 0] - [245, 253, 80]
  shape [180, 140, -5] - [240, 200, 0]
    col [25.000, 0.000, 0.000] dist 0.00080
    col [25.000, 0.000, 0.000] dist 0.00080
  shape [120, 140, -5] - [180, 200, 0]
  shape [180, 200, -5] - [240, 260, 0]
    col [25.000, 0.500, 0.000] dist -0.00000 <-- center of character
resting on ground
  shape [120, 200, -5] - [180, 260, 0]
  shape [180, 140, -5] - [240, 200, 0]
  shape [180, 200, -5] - [240, 260, 0]

While they are not completely comparable (relative vs. absolute
values), you'll see at least the the collision(s) occur where they are
expected. Directly at the center of the character with a distance of
0.

Makes one wonder if it is just a precision issue after all. I'll keep
on debugging.

Kai


P.S.: Attached is a patch to get the output above with the current CVS
code, in case that helps.

debug_output.patch
Description: Binary data