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#include "viewpoint.h"
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
static const vector_t up = {0, 0, 1};
void viewpoint_init(viewpoint_t *view)
{
// Vector from E to T
vector_t t;
vector_sub(&t, &view->target, &view->position);
// Calculate orthogonal vectors to E
vector_t b, v;
vector_cross(&b, (vector_t *)&up, &t);
// Convert to unit-vectors
vector_scale_inv(&t, &t, vector_len(&t));
vector_scale_inv(&b, &b, vector_len(&b));
vector_cross(&v, &t, &b);
// Calculate size of viewplane
COORD_T gx = tanf( FOV / 2 );
COORD_T gy = gx * ((COORD_T)view->height / view->width);
// Calculate viewplane vectors
vector_scale(&view->qx, &b, ( 2 * gx ) / (view->width - 1));
vector_scale(&view->qy, &v, ( 2 * gy ) / (view->height - 1));
// Viewplane starting point
vector_copy(&view->blc, &t);
// This will thrash b and v
vector_sub(&view->blc, &view->blc, vector_scale(&b, &b, gx));
vector_sub(&view->blc, &view->blc, vector_scale(&v, &v, gy));
}
// Calculate ray for viewport w, h
// https://en.wikipedia.org/wiki/Ray_tracing_(graphics)
void viewpoint_ray(viewpoint_t *view, vector_t *r, COORD_T x, COORD_T y)
{
// Calculate ray vector
vector_copy(r, &view->blc);
vector_t t;
vector_scale(&t, &view->qx, x);
vector_add(r, r, &t);
vector_scale(&t, &view->qy, y);
vector_add(r, r, &t);
// Calculate unit vector
vector_scale_inv(r, r, vector_len(r));
}
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