Path: chuka.playstation.co.uk!news
From: Craig Graham <c_graham@hinge.mistral.co.uk>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: 2 Questions - Same Game
Date: Mon, 19 Oct 1998 14:21:16 +0100
Organization: PlayStation Net Yaroze (SCEE)
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John Whitmore wrote:

> Hi,
>     Secondly a maths question, when moving my character around I wish to
> store a vector (x,y) of the direction it is facing so a weapon can be fired
> using this same vector.  how is best to calculate this vector so it can be
> used in this situation?
> I have tried using the rotational value of the sprite, as this is how I am
> changing the visual appearance of the sprite on screen, but with no success.

Using just the libs you get from Sony (with no floating point emulation):

// Setup a direction vector, length is up to you, I'd keep it quite large though
and scale down
// the value later if you need to
SVECTOR direction_vector={10,0,0},rotated_direction;
// Setup a matrix to rotate the vector
MATRIX rotation_matrix=GsIDMATRIX;
// Rotate around Z axis (2d coordinate is in X/Y axis, so rotate around Z)
RotMatrixZ( sprite_rotation_angle,&rotation_matrix);
// Apply the rotation
ApplyMatrixSV(&rotation_matrix,&direction_vector,&rotated_direction);
// Final value is in rotated_direction

Or, faster (in the 2D case) is to use a quick lookup table integer version of
Sin/Cos
(again, no floating point emulation):

// These use my own lookup table trig functions - it's easy to do one
yourself....
direction_vector_x=XSinN(10,sprite_rotation_angle);        // return X*Sin(N)
direction_vector_y=XCosN(10,sprite_rotation_angle);      // return X*Cos(N)

>         Thanks in advance,
>
>                 John

Craig.