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/*------------------------------------------------------------------
camera.c:
XINVADERS 3D - 3d Shoot'em up
Copyright (C) 2000 Don Llopis
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
------------------------------------------------------------------*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "mat4x4.h"
#include "vec4x1.h"
#include "camera.h"
/* local variables */
static float hfov, vfov, hpc, vpc;
static float screen_width, screen_height, half_screen_width,
half_screen_height;
static float aspect_ratio;
static float hadjust, vadjust;
static MAT r_2_l;
void Camera_init ( unsigned int width, unsigned int height, float fov )
{
screen_width = (float) width;
screen_height = (float) height;
half_screen_width = screen_width / 2.0f;
half_screen_height = screen_height / 2.0f;
/* calculate horizontal & vertical field of view */
/* horizontal compensate = HALF_SCREEN_WIDTH / tan ( degrees / 2 )
vertical compensate = HALF_SCREEN_HEIGHT / tan ( degrees / 2 )
see "Building 3d Game Engine" by Brain Hook
*/
hfov = vfov = fov;
hpc = half_screen_width / tan ( hfov/1.5f );
vpc = half_screen_height / tan ( vfov/1.5f );
/* adjust aspect ratio if screen not square ( ie. 4/3 ratio )*/
aspect_ratio = screen_height / screen_height;
/* calculate perspective adjustment values */
hadjust = hpc;
vadjust = (vpc * aspect_ratio);
/* initialize coordinate system conversion mat */
Matrix_id ( r_2_l );
r_2_l[2][2] = -1.0f;
}
void Camera_project_point ( VEC a, int b[2] )
{
if ( a[2] < 0.0 ) {
b[0] = b[1] = 0;
return;
}
b[0] = (int) ( a[0] * hadjust / a[2] + half_screen_width );
b[1] = (int) ( -a[1] * vadjust / a[2] + half_screen_height );
}
void Camera_project_points ( VEC a[], int b[], int n )
{
int i, j;
for ( i=0, j=0; i<n; i++, j+=2 )
{
b[j] = (int) ( a[i][0] * hadjust / a[i][2] + half_screen_width );
b[j+1] = (int) ( -a[i][1] * vadjust / a[i][2] + half_screen_height );
}
}
void Camera_transform ( MAT r, VEC up, VEC from, VEC at )
{
VEC x, y, z, tmp, pos;
MAT tmp_mat;
/* initialize transformation mat */
Matrix_id ( tmp_mat );
/* calculate view plane normal -- or view-z-axis */
Vector_sub ( from, at, z );
Vector_norm ( z );
/* calculate view-x-axis */
Vector_cross ( up, z, x );
Vector_norm ( x );
/* calculate view-y-axis */
Vector_cross ( z, x, y );
/* place axis-vecs into transformation mat
To understand how this works see chapter 5
and 6 of "Computer Graphics Principles & Practice"
*/
Matrix_set_xrow ( tmp_mat, x );
Matrix_set_yrow ( tmp_mat, y );
Matrix_set_zrow ( tmp_mat, z );
/* get camera's world position and rotate it
into camera coordinate system. This becomes
the new translation which is to be applied
to an object's vertices inorder to make its
position relative to the camera coordinate system
see chapter 6
*/
Vector_copy ( from, tmp );
Vector_negate ( tmp );
Matrix_vec_mult ( tmp_mat, tmp, pos );
Matrix_set_trans ( tmp_mat, pos );
/* now change from right hand coordinate system
to left hand coordinate system
leaving the result in 'r'
*/
Matrix_mult ( r_2_l, tmp_mat, r );
}
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