transform.c

#include "transform.h"

// Matrix update, calculate transform = world * view * projection (matrix multiplication)
void transform_update(transform_t *ts) {
	matrix_t m;
	matrix_mul(&m, &ts->world, &ts->view);
	matrix_mul(&ts->transform, &m, &ts->projection);
}

//Initialize, set the screen length and width and calculate the perspective transformation matrix
void transform_init(transform_t *ts, int width, int height) {
	float aspect = (float)width / ((float)height);
	matrix_set_identity(&ts->world);
	matrix_set_identity(&ts->view);
	matrix_set_perspective(&ts->projection, 3.1415926f * 0.5f, aspect, 1.0f, 500.0f);
	ts->w = (float)width;
	ts->h = (float)height;
	transform_update(ts);
}

// Project the vector x to the screen, and the result is stored in y
void transform_apply(const transform_t *ts, vector_t *y, const vector_t *x) {
	matrix_apply(y, x, &ts->transform);
}

// Check the boundaries of homogeneous coordinates and cvv for frustum clipping (return 0 if it is in the visible area)
int transform_check_cvv(const vector_t *v) {
	float w = v->w;
	int check = 0;
	if (v->z < 0.0f) check |= 1;
	if (v->z >  w) check |= 2;
	if (v->x < -w) check |= 4;
	if (v->x >  w) check |= 8;
	if (v->y < -w) check |= 16;
	if (v->y >  w) check |= 32;
	return check;
}

//Normalize to get screen coordinates (x, y, z, w) -> (x/w, y/w, z/w, 1)
void transform_homogenize(const transform_t *ts, vector_t *y, const vector_t *x) {
	float rhw = 1.0f / x->w;
	y->x = (x->x * rhw + 1.0f) * ts->w * 0.5f;
	y->y = (1.0f - x->y * rhw) * ts->h * 0.5f;
	y->z = x->z * rhw;
	y->w = 1.0f;
}