Re: [boost] Library Proposal: Boost.Geom 2D and 3DGeometricPrimitives

From: Martin Slater (mslater_at_[hidden])
Date: 2005-07-02 06:41:57

> Ok ! Consider this: We are writing a 2D Game using SDL. Each time we
> move something on the screen we must remember its last and new position (two 
> rectangles)
> so that we can redraw that area and update the screen (we call this, a dirty 
> rectangle
> mechanisim) So at each frame we construct the region of the screen that has to 
> be redrawen
> before calling SDL_UpdateRects to update the screen. The region is constructed 
> 60 times per second (this the refresh rate of most screens), do you think 
> that the game writer will want to convert a vector<rectangle> (whose size may 
> vary
> between 0 and 100) into the corresponding
> vector<SDL_Rect> 60 times per second ? And remember there is far more stuff to
> be done in this 1/60 of a second.

Have you actually profiled this?  I was quite happily acheiving much 
higher framerates than 60fps with dirty update region based 2d graphics 
on windows boxes nearly 10 years ago and using just a simple struct 
containing a pair of int's to represent a point that converted to 
windows points as neccesary. This is so unlikely to be any sort of 
bottleneck in the system, numbers would be good to back this up as it 
seems to be the fundamental reason behind the design of the library.

I can imagine scenerios where the conversion could become a problem but 
yours as described just isn't one of them;)

Also I think that as soon as you write a geometric library that contains 
points you need to introduce vectors and hence matrices (with probably 
homegenous forms) so you can simply set up the entire world -> device 
tranform pipeline. Without these the library just doesn't offer enough 
out of the box to make it interesting to me. Even then it would have to 
be very good to compete with Eberly's wild magic library as an off the 
shelf type of library.

Martin

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