SpritesMind.Net

Orion_ wrote:I'm really impressed by your starfox demo because, showing a 3D cube is something, but navigating in a 3D world is a whole lot more
In all my attempts to do a 3D engine, I never managed to get rid of fixed point overflow when polygons starts to get out of screen
how do you manage to do proper 3D clipping without 3D coordinates doing overflow ? I heard about frustum culling but, it require lots of math and still your demo is pretty fast doing all of this on a single 7.6mhz processor + the tile constraint
I'm really not good at math >_<

Stef wrote:Gasega68k>
I tested the different 3D tests and the only difference i could see with the hprec and normal is that hprec is less accurate when you zoom in on object !
I guess it has something to do with the global coordinates system, allowing far distance view but at the cost of low near accuracy.
The textured car is really impressive ! Imagine a game made of it (mixing flat and textures objects) on the sega genesis X'D

Orion>With the 68000 you are somehow limited to 16 bits numbers for fixed point operations as the native division and multiplication does 16x16=32 or 32:16=16. Hopefully 16 bits fixed point is not that bad to work with. In SGDK i use a fix16 type where:
- 1 bit is used for sign
- 9 bits for integer part
- 6 bits for frationnal part

This way you can have -512 to 512 range values with fractionnal part (1/64 step for fractionnal part). I believe is a nice compromise =)

static fixed_t FIX_MUL( fixed_t a, fixed_t b )
{
    fixed_t res = 0, c = 0, d = 0, e = 0;
    asm volatile (
        "tst.l %1\n\t"
        "spl %5\n\t"
        "bpl.b 1f\n\t"
        "neg.l %1\n"
        "1:\n\t"
        "tst.l %2\n\t"
        "bpl.b 2f\n\t"
        "not.b %5\n\t"
        "neg.l %2\n"
        "2:\n\t"
        "move.w %1,%3\n\t"
        "swap %1\n\t"
        "move.w %2,%4\n\t"
        "move.w %2,%0\n\t"
        "swap %2\n\t"
        "mulu %3,%0\n\t"
        "mulu %1,%4\n\t"
        "mulu %2,%1\n\t"
        "mulu %3,%2\n\t"
        "swap %1\n\t"
        "move.w #0,%1\n\t"
        "move.w #0,%0\n\t"
        "swap %0\n\t"
        "add.l %4,%0\n\t"
        "addx.l %2,%0\n\t"
        "addx.l %1,%0\n\t"
        "tst.b %5\n\t"
        "bne.b 3f\n\t"
        "neg.l %0\n"
        "3:\n\t"
        : "=d" (res), "=d" (a), "=d" (b), "=d" (c), "=d" (d), "=d" (e)
        : "0" (res), "1" (a), "2" (b), "3" (c), "4" (d), "5" (e)
        : "cc"
    );
    return(res);
}

r57shell wrote:How about that? http://en.wikipedia.org/wiki/Karatsuba_algorithm
It's very easy and using 3 multiply operations.

A more efficient implementation of Karatsuba multiplication can be set as [5]

x y = (b^2 + b)x1y1 − b(x1 − x0)(y1 − y0) + (b + 1)x0y0,

where b is the weight of x1.

Chilly Willy wrote:See, (b^2 + b)x1y1 is multiplying THREE terms, not two. Ditto for the rest.