Games/XInvaders3D/camera.c

   1 /*------------------------------------------------------------------
   2   camera.c:
   3
   4     XINVADERS 3D - 3d Shoot'em up
   5     Copyright (C) 2000 Don Llopis
   6
   7     This program is free software; you can redistribute it and/or modify
   8     it under the terms of the GNU General Public License as published by
   9     the Free Software Foundation; either version 2 of the License, or
  10     (at your option) any later version.
  11
  12     This program is distributed in the hope that it will be useful,
  13     but WITHOUT ANY WARRANTY; without even the implied warranty of
  14     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15     GNU General Public License for more details.
  16
  17     You should have received a copy of the GNU General Public License
  18     along with this program; if not, write to the Free Software
  19     Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  20
  21 ------------------------------------------------------------------*/
  22 #include <stdio.h>
  23 #include <stdlib.h>
  24 #include <math.h>
  25
  26 #include "mat4x4.h"
  27 #include "vec4x1.h"
  28 #include "camera.h"
  29
  30 /* local variables */
  31 static float hfov, vfov, hpc, vpc;
  32 static float screen_width, screen_height, half_screen_width,
  33              half_screen_height;
  34 static float aspect_ratio;
  35 static float hadjust, vadjust;
  36 static MATRIX4 r_2_l;
  37
  38
  39 void Camera_init ( unsigned int width, unsigned int height, float fov )
  40 {
  41   screen_width       = (float) width;
  42   screen_height      = (float) height;
  43   half_screen_width  = screen_width / 2.0f;
  44   half_screen_height = screen_height / 2.0f;
  45
  46   /* calculate horizontal & vertical field of view */
  47
  48   /* horizontal compensate = HALF_SCREEN_WIDTH / tan ( degrees / 2 )
  49      vertical compensate = HALF_SCREEN_HEIGHT / tan ( degrees / 2 )
  50
  51      see "Building 3d Game Engine" by Brain Hook
  52   */
  53
  54   hfov = vfov = fov;
  55
  56   hpc = half_screen_width / tan ( hfov/1.5f );
  57   vpc = half_screen_height / tan ( vfov/1.5f );
  58
  59   /* adjust aspect ratio if screen not square ( ie. 4/3 ratio )*/
  60   aspect_ratio = screen_height / screen_height;
  61
  62
  63   /* calculate perspective adjustment values */
  64   hadjust = hpc;
  65   vadjust = (vpc * aspect_ratio);
  66
  67   /* initialize coordinate system conversion mat */
  68   Matrix_id ( r_2_l );
  69   r_2_l[2][2] = -1.0f;
  70
  71 }
  72
  73 void Camera_project_point ( VECTOR4 a, int b[2] )
  74 {
  75    if ( a[2] < 0.0 ) {
  76       b[0] = b[1] = 0;
  77       return;
  78    }
  79   b[0] = (int) ( a[0] * hadjust / a[2] + half_screen_width );
  80   b[1] = (int) ( -a[1] * vadjust / a[2] + half_screen_height );
  81 }
  82
  83 void Camera_project_points ( VECTOR4 a[], int b[], int n )
  84 {
  85    int i, j;
  86
  87    for ( i=0, j=0; i<n; i++, j+=2 )
  88    {
  89      b[j] = (int) ( a[i][0] * hadjust / a[i][2] + half_screen_width );
  90      b[j+1] = (int) ( -a[i][1] * vadjust / a[i][2] + half_screen_height );
  91    }
  92 }
  93
  94 void Camera_transform ( MATRIX4 r, VECTOR4 up, VECTOR4 from, VECTOR4 at )
  95 {
  96   VECTOR4 x, y, z, tmp, pos;
  97   MATRIX4 tmp_mat;
  98
  99   /* initialize transformation mat */
 100   Matrix_id ( tmp_mat );
 101
 102   /* calculate view plane normal -- or view-z-axis */
 103   Vector_sub ( from, at, z );
 104   Vector_norm ( z );
 105
 106   /* calculate view-x-axis */
 107   Vector_cross ( up, z, x );
 108   Vector_norm ( x );
 109
 110   /* calculate view-y-axis */
 111   Vector_cross ( z, x, y );
 112
 113   /* place axis-vecs into transformation mat
 114      To understand how this works see chapter 5
 115      and 6 of "Computer Graphics Principles & Practice"
 116    */
 117   Matrix_set_xrow ( tmp_mat, x );
 118   Matrix_set_yrow ( tmp_mat, y );
 119   Matrix_set_zrow ( tmp_mat, z );
 120
 121   /* get camera's world position and rotate it
 122      into camera coordinate system. This becomes
 123      the new translation which is to be applied
 124      to an object's vertices inorder to make its
 125      position relative to the camera coordinate system
 126      see chapter 6
 127   */
 128   Vector_copy ( from, tmp );
 129   Vector_negate ( tmp );
 130   Matrix_vec_mult ( tmp_mat, tmp, pos );
 131   Matrix_set_trans ( tmp_mat, pos );
 132
 133   /* now change from right hand coordinate system
 134      to left hand coordinate system
 135      leaving the result in 'r'
 136   */
 137   Matrix_mult ( r_2_l, tmp_mat, r );
 138 }