155 lines
2.8 KiB
C
155 lines
2.8 KiB
C
/** \file
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* 3D camera equation.
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*
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* Given a camera matrix and a XYZ point, returns the 2D coordinate
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* of the point.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include "camera.h"
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struct _camera_t
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{
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float near;
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float far;
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m44_t r;
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};
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camera_t *
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camera_new(
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v3_t eye,
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v3_t lookat,
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v3_t up,
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float fov
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)
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{
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camera_t * c = calloc(1, sizeof(*c));
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if (!c)
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return NULL;
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camera_setup(c, eye, lookat, up, fov);
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return c;
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}
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void
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camera_setup(
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camera_t * const c,
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v3_t eye,
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v3_t lookat,
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v3_t up,
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float fov
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)
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{
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// compute the basis for the camera
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// negative look direction from eye to destination
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v3_t w = v3_norm(v3_sub(eye, lookat));
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// compute the side axis
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v3_t u = v3_norm(v3_cross(up, w));
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// and the "up" normal
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v3_t v = v3_norm(v3_cross(w, u));
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m44_t cam = {{
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{ u.p[0], u.p[1], u.p[2], -v3_dot(u,eye) },
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{ v.p[0], v.p[1], v.p[2], -v3_dot(v,eye) },
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{ w.p[0], w.p[1], w.p[2], -v3_dot(w,eye) },
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{ 0, 0, 0, 1 },
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}};
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fprintf(stderr, "Camera:\n");
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for(int i = 0 ; i < 4 ; i++)
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{
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for(int j = 0 ; j < 4 ; j++)
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fprintf(stderr, " %+5.3f", cam.m[i][j]);
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fprintf(stderr, "\n");
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}
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// now compute the perspective projection matrix
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if(1) {
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float s = 1000.0 / tan(fov * M_PI / 180 / 2);
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c->near = 1;
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c->far = 200;
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float f1 = - c->far / (c->far - c->near);
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float f2 = - c->far * c->near / (c->far - c->near);
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m44_t pers = {{
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{ s, 0, 0, 0 },
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{ 0, s, 0, 0 },
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{ 0, 0, f2, -1 },
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{ 0, 0, f1, 0 },
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}};
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fprintf(stderr, "Perspective:\n");
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for(int i = 0 ; i < 4 ; i++)
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{
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for(int j = 0 ; j < 4 ; j++)
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fprintf(stderr, " %+5.3f", pers.m[i][j]);
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fprintf(stderr, "\n");
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}
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m44_mult(&c->r, &pers, &cam);
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} else {
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// no perspective
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m44_t pers = {{
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{ 1, 0, 0, 0 },
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{ 0, 1, 0, 0 },
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{ 0, 0, 1, 0 },
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{ 0, 0, 0, 1 },
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}};
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// and apply it to the camera matrix to generate transform
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m44_mult(&c->r, &pers, &cam);
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}
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fprintf(stderr, "Cam*Pers\n");
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for(int i = 0 ; i < 4 ; i++)
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{
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for(int j = 0 ; j < 4 ; j++)
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fprintf(stderr, " %+5.3f", c->r.m[i][j]);
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fprintf(stderr, "\n");
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}
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}
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/** Transform a XYZ point into a screen point.
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*
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* Returns 0 if this is behind us. Perhaps it should do a z buffer?
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* https://en.wikipedia.org/wiki/3D_projection
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*/
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int
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camera_project(
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const camera_t * const c,
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const v3_t * const v_in,
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v3_t * const v_out
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)
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{
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v4_t v = {{ v_in->p[0], v_in->p[1], v_in->p[2], 1 }};
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v4_t p = m44_multv(&c->r, &v);
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//p.p[2] *= -1;
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// what if p->p[4] == 0?
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// pz < 0 == The point is behind us; do not display?
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//if (p[2] < c->near || p[2] > c->far)
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if (p.p[2] <= 0)
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return 0;
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// shrink by the distance
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p.p[0] *= 1.0 / p.p[3];
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p.p[1] *= 1.0 / p.p[3];
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//p[2] /= 1000;
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// Transform to screen coordinate frame,
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// and return it to the caller
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v_out->p[0] = p.p[0];
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v_out->p[1] = p.p[1];
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v_out->p[2] = p.p[2];
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return 1;
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}
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