Re: [pygame] Physics, collision detection etc?

["Nirav Patel" <olpc@xxxxxxxxxxxxxx>]

Peter,

The idea isn't to make a mask of the entire world.  You make a mask of
each individual Surface and provide the offset of where it is in the
world relative to the Surface you're checking collision with to the
Mask overlap functions.  This is quite fast, even checking dozens of
objects against each other, because in the very common case that the
offsets make it so the objects can't overlap, it doesnt bother
calculating it and just returns false.

Nirav

On Thu, Oct 9, 2008 at 11:46 AM, Peter Gebauer
<peter.gebauer@xxxxxxxxxxxxxxxxxxxxx> wrote:
> Hello René.
>
> The thing is, in a large world spanning 16000x10000 pixels that will be a
> huge mask. Even if I reduce the resolution of the mask alone it will be
> either top inprecise or still too large.
>
> I don't want to write for OpenGL alone even though the plan is to use OpenGL
> as test output. My plan is to build a large world of 3 or 4-sided
> convex polygons that could be used to detect colliding with large shapes in
> that world.
>
> The best way to do this is probably to expose some of Zhang Fan's physics
> code, much of the math involved is already there, it just lacks
> non-rectangular shapes and a nice Python API to access it.
>
> /Peter
>
> On 2008-10-09 (Thu) 11:41, René Dudfield wrote:
>> hi,
>>
>> Note, that you can find contact normals with the mask module. See mask example.
>>
>> For some types of games, per pixel collision detection is fast enough.
>>  It uses rect bounding boxes as a first pass, so mostly it's not much
>> slower than rect collision detection.  Assuming you are working in 2d,
>> and you cache the mask(not regenerating it every frame) that is.
>> However the mask.from_surface routine is fairly fast, it could do with
>> some more optimization.
>>
>> For opengl, it'd be interesting to do it in a shader too... since then
>> you could just reuse your drawing routines to draw your
>> objects(sprites) into a buffer (each with a different color), then use
>> a shader to find all of the contact normals.  That way your collision
>> could be pixel perfect, even with different methods of
>> drawing(cartoon, glow, and other shaders) where the polygon
>> representation is not correct.
>>
>>
>> cheers,
>>
>>
>>
>>
>> On Wed, Oct 8, 2008 at 9:46 PM, Greg Ewing <greg.ewing@xxxxxxxxxxxxxxxx> wrote:
>> > Nirav Patel wrote:
>> >
>> >> If the polygons are Surfaces or can be turned into Surfaces, they can
>> >> be turned into Masks to do pixel collision.
>> >>
>> >> On Tue, Oct 7, 2008 at 11:21 AM, Peter Gebauer
>> >> <peter.gebauer@xxxxxxxxxxxxxxxxxxxxx> wrote:
>> >>
>> >> > Yep, but as I said, I need to find colliding polygons, not pixels.
>> >
>> > Pixel collision isn't suitable for all purposes,
>> > e.g. if you need to find contact normals for
>> > physics calculations.
>> >
>>
>